In addition to the reported Neanderthal and Denisovan introgressions, our results support a third introgression in all Asian and Oceanian populations from an archaic population. This population is either related to the Neanderthal-Denisova clade or diverged early from the Denisova lineage.
(Congratulations to the authors, Mondal, Bertranpetit, and Lao.)
Here we report an analysis comparing cultural and genetic data from 13 populations from in and around Northeast Asia spanning 10 different language families/isolates. We construct distance matrices for language (grammar, phonology, lexicon), music (song structure, performance style), and genomes (genome-wide SNPs) and test for correlations among them. … robust correlations emerge between genetic and grammatical distances. Our results suggest that grammatical structure might be one of the strongest cultural indicators of human population history, while also demonstrating differences among cultural and genetic relationships that highlight the complex nature of human cultural and genetic evolution.
I feel like there’s a joke about grammar Nazis in here.
While humans average seven hours, other primates range from just under nine hours (blue-eyed black lemurs) to 17 (owl monkeys). Chimps, our closest living evolutionary relatives, average about nine and a half hours. And although humans doze for less time, a greater proportion is rapid eye movement sleep (REM), the deepest phase, when vivid dreams unfold.
Sleep is pretty much universal in the animal kingdom, but different species vary greatly in their habits. Elephants sleep about two hours out of 24; sloths more than 15. Individual humans vary in their sleep needs, but interestingly, different cultures vary greatly in the timing of their sleep, eg, the Spanish siesta. Our modern notion that people “should” sleep in a solid, 7-9 hour chunk (going so far as to “train” children to do it,) is more a result of electricity and industrial work schedules than anything inherent or healthy about human sleep. So if you find yourself stressed out because you keep taking a nap in the afternoon instead of sleeping through the night, take heart: you may be completely normal. (Unless you’re tired because of some illness, of course.)
Within any culture, people also prefer to rest and rise at different times: In most populations, individuals range from night owls to morning larks in a near bell curve distribution. Where someone falls along this continuum often depends on sex (women tend to rise earlier) and age (young adults tend to be night owls, while children and older adults typically go to bed before the wee hours).
Genes matter, too. Recent studies have identified about a dozen genetic variations that predict sleep habits, some of which are located in genes known to influence circadian rhythms.
While this variation can cause conflict today … it may be the vestige of a crucial adaptation. According to the sentinel hypothesis, staggered sleep evolved to ensure that there was always some portion of a group awake and able to detect threats.
So they gave sleep trackers to some Hadza, who must by now think Westerners are very strange, and found that at any particular period of the night, about 40% of people were awake; over 20 nights, there were “only 18 one-minute periods” when everyone was asleep. That doesn’t prove anything, but it does suggest that it’s perfectly normal for some people to be up in the middle of the night–and maybe even useful.
In May, a pair of papers published by separate teams in the journal Cell focused on the NOTCH family of genes, found in all animals and critical to an embryo’s development: They produce the proteins that tell stem cells what to turn into, such as neurons in the brain. The researchers looked at relatives of the NOTCH2 gene that are present today only in humans.
In a distant ancestor 8 million to 14 million years ago, they found, a copying error resulted in an “extra hunk of DNA,” says David Haussler of the University of California, Santa Cruz, a senior author of one of the new studies.
This non-functioning extra piece of NOTCH2 code is still present in chimps and gorillas, but not in orangutans, which went off on their own evolutionary path 14 million years ago.
About 3 million to 4 million years ago, a few million years after our own lineage split from other apes, a second mutation activated the once non-functional code. This human-specific gene, called NOTCH2NL, began producing proteins involved in turning neural stem cells into cortical neurons. NOTCH2NL pumped up the number of neurons in the neocortex, the seat of advanced cognitive function. Over time, this led to bigger, more powerful brains. …
The researchers also found NOTCH2NL in the ancient genomes of our closest evolutionary kin: the Denisovans and the Neanderthals, who had brain volumes similar to our own.
“Genomes that evolve in different geographic locations without intermixing can end up being different from each other,” said Kateryna Makova, Pentz Professor of Biology at Penn State and an author of the paper. “… This variation has a lot of advantages; for example, increased variation in immune genes can provide enhanced protection from diseases. However, variation in geographic origin within the genome could also potentially lead to communication issues between genes, for example between mitochondrial and nuclear genes that work together to regulate mitochondrial function.”
Researchers looked at recently (by evolutionary standards) mixed populations like Puerto Ricans and African Americans, comparing the parts of their DNA that interact with mitochondria to the parts that don’t. Since mitochondria hail from your mother, and these populations have different ethnic DNA contributions along maternal and paternal lines. If all of the DNA were equally compatible with their mitochondria, then we’d expect to see equal contributions to the specifically mitochondria-interacting genes. If some ethnic origins interact better with the mitochondria, then we expect to see more of this DNA in these specific places.
The latter is, in fact, what we find. Puerto Ricans hail more from the Taino Indians along their mtDNA, and have relatively more Taino DNA in the genes that affect their mitochondria–indicating that over the years, individuals with more balanced contributions were selected against in Puerto Rico. (“Selection” is such a sanitized way of saying they died/had fewer children.)
This indicates that a recently admixed population may have more health issues than its parents, but the issues will work themselves out over time.
In The Blank Slate, Steven Pinker gives about the best recommendation I can think of for Wilson’s book:
At Harvard there were leaflets and teach-ins, a protester with a bullhorn calling for Wilson’s dismissal, and invasions of his classroom by slogan-shouting students. When he spoke at other universities, posters called him the “Right-Wing-Prophet of Patriarchy” and urged people to bring noisemakers to his lectures. Wilson was about to speak at a 1978 meeting of the American Association for the Advancement of Science when a group of people carrying placards (one with a swastika) rushed onto the stage chanting, “Racist Wilson, you can’t hide, we charge you with genocide.” One protester grabbed the microphone and harangued the audience while another doused Wilson with a pitcher of water.
Pretty intense for a guy whose career is mostly about ants.
Since it is easier to remember what you have read if you take notes and then transcribe them, and this thing is 574 pages long, I’ll be transcribing some of my notes here as I go along.
The book gives lots of interesting examples of different concepts. For example, in the section on parasitism, there’s an example of a variety of termite that moves into and eats the nests of other termites, thus making a termite mound-in-a-mound, I suppose. To be fair, some termite mounds are about as big as a house and so this is a totally reasonable thing for termites to do.
Chapter 1: The morality of the Gene
Camus said that the only serious philosophical question is suicide.
That is wrong even in the strict sense intended. …
From now on, let’s use “” instead of blockquotes.
Chapter 2: Elementary Concepts
“Genes, like Leibnitz’s monads, have no windows; the higher properties of life are emergent. To specify an entire cell, we are compelled to provide not only the nucleotide sequences but also the identity and configuration of other kinds of molecules placed in and around the cells. To specify an organism requires still more information about both the properties of the cells and their spacial positions. And once assembled, organisms have no windows. A society can be described only as a set of particular organisms, and even then it is difficult to extrapolate the joint activity of this ensemble from the instant of specification, that is, to predict social behavior. …
“Society: a group of individuals belonging to the same species and organized in a cooperative manner. … Yet aggregation, sexual behavior, and territoriality are important properties of true societies, and they are correctly referred to as social behavior. … Since the bond of the society is simply and solely communication, its boundaries can be defined in terms of the curtailment of communication.”
EvX: I have been thinking for a long time about language as effective barriers of culture. Not that culture can’t cross language barriers (movies get dubbed all the time,) but it’s much harder. And since some languages are easier to learn than others, (eg, Finnish is harder than German if you speak English,) cross-language communication is probably easier between some groups than others. The Finns (and a few other European groups) speak non-Indo-European languages, which might make them more functionally isolated within the European context than, say, their neighbors in Sweden.
Back to Wilson:
“Individual: Any physically distinct organism… The distinction between the individual and the colony can be especially baffling in the sponges. … [Hah.]
“Population: A set of organisms belonging to the same species and occupying a clearly delimited area at the same time. This unit… is defined in terms of genetic continuity. In the case of sexually reproducing organisms, the population is a geographically delimited set of organisms capable of freely interbreeding with one another under natural conditions. …
“In sexually reproducing forms, including the vast majority of social organisms, a species is a population or set of populations within which the individuals are capable of freely interbreeding under natural conditions. By definition the members of the species do not interbreed freely with those of other species, however closely related they may be genetically. … In establishing the limits of a species it is not enough merely to prove that genes of two or more populations can be exchanged under experimental conditions. The population must be demonstrated to interbreed fully in the free state.”
[Example: Lions and Tigers can interbreed, yet even in places where their ranges historically overlapped, no one ever reported finding wild ligers or tigons. While they can interbreed in zoos, their behavior is different enough in the wild that it doesn’t happen.]
EvX: And here’s where people ask about Sapiens and Neanderthals. Yes, they interbred. But it looks like they didn’t interbreed much (while they bred plenty with their own,) and it also looks like there’s been a fair amount of selection against Neanderthal DNA in modern humans, winnowing down the genes passed on to us. For example, there’s pretty much no Neanderthal DNA on the Y chromosome, suggesting that any sons of Neanderthal-Sapiens unions were infertile (or didn’t make it at all.) There’s also no (known) Neanderthal mtDNA, suggesting that the matings that did happen involved Neanderthal men with Sapiens women–or if the opposite pairing happened, those children were brought into Neanderthal tribes. At any rate, the pattern is far from complete interfertility.
Back to Wilson:
“A population that differs significantly from other populations belonging to the same species is referred to as a geographic race or subspecies. Subspecies are separated from other subspecies by distance and geographic barriers that prevent the exchange of individuals, as opposed to the genetically based “intrinsic isolating mechanisms” that hold species apart. Subspecies, insofar as they can be distinguished with any objectivity at all, show every conceivable degree of differentiation from other subspecies. At one extreme are the populations that fall along a cline–a simple gradient in the geographic variation of a given character. In other words, a character that varies in a clinal pattern is one that changes gradually over a substantial portion of the entire range of the species. At the other extreme are subspecies consisting of easily distinguished populations that are differentiated from one another by numerous genetic traits and exchange genes across a narrow zone of intergradation.
The main obstacle in dealing with the population as a unit… is the practical difficulty of deciding the limits of particular populations.”
EvX: I would like to point out that humans made up these words to carve up a part of reality that doesn’t always carve that easily. For example, it may be obvious that a wolf species that ranges over thousands of miles is pretty different at the far east and far western extent of its range, but there may be no exact spot in between where the eastern type ends and the western type begins. By contrast, sometimes in human societies you have groups of genetically and culturally distinct people separated for centuries by little more than a road, a wall, a religion, or a language. There is no a priori reason to think that one of these cases fits the definition and the other does not.
But the language we use to delineate groups of ants or wolves or fungi is not the language we use to delineate humans, not just because we wish to be inaccurate, but also because we generally wish to show each other respect. We do so by avoiding language normally reserved for non-humans and using special terms for humans, eg, my offspring are normally referred to as my “children.”
Back to Wilson.
“What is the relation between the population and the society? Here we arrive unexpectedly at the crux of theoretical sociobiology. The distinction between the two categories is essentially as follows: the population is bounded by a zone of sharply reduced gene flow, while the society is bounded by a zone of sharply reduced communication. Often the two zones are the same…
The Multiplier Effect
“Social organization is the class of phenotypes furthest removed from the genes. It is derived jointly from the behavior of the individuals and the demographic properties of the population… A small evolutionary change in the behavior pattern of individuals can be amplified into a major social effect by the expanding upward distribution of the effect into multiple facets of life. …
“Even stronger multiplier effects occur in the social insects. … The structure of nests alone can be used to distinguish species within the higher termites.”
EvX: There follows an interesting description of how termites build their mounds, also known as “termitaries.”
“Multiplier effects can speed social evolution still more when an individual’s behavior is strongly influenced by the particularities of its social experience. This process, called socialization, becomes increasingly becomes increasingly prominent as one moves upward phylogenetically into more intelligent species, and it reaches its maximum influence in the higher primates. Although the evidence is still largely inferential, socialization appears to amplify phenotypic differences among primate species. …
S”ocialization can also amplify genetically based variation of individual behavior within troops. The temperament and rank of a higher primate is strongly influenced by its early experiences with its peers and its mother.”
EvX: This is a really interesting idea. We hear constantly that ideas like race and gender are social constructs, but what exactly a social construct is we hear far less often. The implication–at least as the phrases are employed–is that they are not real at all, that they are make believe, that we have chosen some random and arbitrary place to carve up reality and that we could use some other random place just as well, but Wilson provides a much better conception: “social constructs” are really amplified ideas about the world around us. In other words, they’re exaggerated stereotypes.
For example, let’s imagine a world in which the average male is taller than the average female, but there’s a lot of variety in height and so there are many individual men who are shorter than a good chunk of women, and likewise many women who are taller than a decent chunk of men. The idea that “men are taller than women” is of course true on average, but also an exaggeration. Men who are particularly short and women who are particularly tall may dislike the fact that they don’t match this Platonic ideal.
Back to Wilson:
“The Evolutionary Pacemaker and Social Drift
“…when evolution involves both structure and behavior, behavior should change first and then structure. In other words, behavior should be the evolutionary pacemaker. … Social behavior also frequently serves as an evolutionary pacemaker. The entire process of ritualization, during which a behavior is transformed by evolution into a more efficient signaling device, typically involves a behavioral change followed by morphological alterations that enhance the visibility and distinctiveness of the behavior.
“The relative lability of behavior leads inevitably to social drift, the random divergence in the behavior and mode of organization of societies or groups of societies. …
“The amount of variance within a population of societies is the sum of the variations due to genetic drift, tradition drift, and their interaction. … Even if the alteration to social structure of a group is due to a behavioral change in a key individual, we cannot be sure that this member was not predisposed to the act by a distinctive capability or temperament conferred by a particular set of genes …
“…Cavalli-Sforza and Feldman (1973) have suggested that in human social evolution the equivalent of an important mutation is a new idea. If it is acceptable and advantageous, the idea will spread quickly. If not, it will decline in frequency and he forgotten. Tradition drift in such instances, like purely genetic drift, has stochastic properties amenable to mathematical analysis.”
EvX: Good old memes. How I love them.
“All true societies are differentiated populations. When cooperative behavior evolves it is put to service by one kind of individual on behalf of another, either unilaterally or mutually…
“The proportions of the demographic classes [like old and young people] also affect the fitness of the group and, ultimately, of each individual member… a deviant population allowed to reproduce for one to several generations will go far to restore the age distribution of populations normal for the species.”
EvX: By “deviant population” he means a population that has more or less of a particular class than is ideal, like if an ant colony lost half of its workers in an accident or a plague wiped out most of the children in a society.
“Only if its growth is zero when averaged over many generations can the population have a chance of long life. There is one remaining way to be a success. A population headed for extinction can still possess a high degree of fitness if it succeeds in sending out propagules and creates new populations elsewhere.”
Kuru is an acquired prion disease largely restricted to the Fore linguistic group of the Papua New Guinea Highlands, which was transmitted during endocannibalistic feasts. Heterozygosity for a common polymorphism in the human prion protein gene (PRNP) confers relative resistance to prion diseases. Elderly survivors of the kuru epidemic, who had multiple exposures at mortuary feasts, are, in marked contrast to younger unexposed Fore, predominantly PRNP 129 heterozygotes. Kuru imposed strong balancing selection on the Fore, essentially eliminating PRNP 129 homozygotes. Worldwide PRNP haplotype diversity and coding allele frequencies suggest that strong balancing selection at this locus occurred during the evolution of modern humans.
Our ancestors–the ancestors of all humans–ate each other so often that they actually evolved resistance to prion diseases.
Chapter 7 of The 10,000 Year Explosion is about the evolution of high Ashkenazi IQ; chapter 8 is the Conclusion, which is just a quick summary of the whole book. (If you’re wondering if you would enjoy the book, try reading the conclusion and see if you want to know more.)
This has been an enjoyable book. As works on human evolution go, it’s light–not too long and no complicated math. Pinker’s The Blank Slate gets into much more philosophy and ethics. But it also covers a lot of interesting ground, especially if you’re new to the subject.
I have seen at least 2 people mention recently that they had plans to respond to/address Cochran and Harpending’s timeline of Jewish history/evolution in chapter 7. I don’t know enough to question the story, so I hope you’ll jump in with anything enlightening.
The basic thesis of Chapter 7 is that Ashkenazi massive over-representation in science, math, billionaires, and ideas generally is due to their massive brains, which is due in turn to selective pressure over the past thousand years or so in Germany and nearby countries to be good at jobs that require intellect. The authors quote the historian B. D. Weinryb:
More children survived to adulthood in affluent families than in less affluent ones. A number of genealogies of business leaders, prominent rabbis, community leaders, and the like–generally belonging to the more affluent classes–show that such people often had four, six, sometimes even eight or nice children who reached adulthood…
Weinryb cites a census of the town of Brody, 1764: homeowner household had 1.2 children per adult; tenant households had only 0.6.
As evidence for this recent evolution, the authors point to the many genetic diseases that disproportionately affect Ashkenazim:
Tay-Sachs disease, Gaucher’s disease, familial dysautonomia, and two different forms of hereditary breast cancer (BRCA1 and BRCA2), and these diseases are up to 100 times more common in Ashkenazi Jews than in other European populations. …
In principle, absent some special cause, genetic diseases like these should be rare. New mutations, some of which have bad effects, appear in every generation, but those that cause death or reduced fertility should be disappearing with every generation. … one in every twenty-five Ashkenazi Jews carries a copy of the Tay-Sachs mutation, which kills homozygotes in early childhood. This is an alarming rate.
What’s so special about these diseases, and why do the Ashkenazim have so darn many of them?
Some of them look like IQ boosters, considering their effects on the development of the central nervous system. The sphingolipid mutations, in particular, have effects that could plausibly boost intelligence. In each, there is a buildup of some particular sphingolipid, a class of modified fat molecules that play a role in signal transmission and are especially common in neural tissues. Researchers have determined that elevated levels of those sphingolipids cause the growth of more connections among neurons..
There is a similar effect in Tay-Sachs disease: increased levels of a characteristic storage compound… which causes a marked increase in the growth of dendrites, the fine branches that connect neurons. …
We looked at the occupations of patients in Israel with Gaucher’s disease… These patients are much more likely to be engineers or scientists than the average Israeli Ashkenazi Jew–about eleven times more likely, in fact.
Basically, the idea is that similar to sickle cell anemia, being heterozygous for one of these traits may make you smarter–and being homozygous might make your life considerably shorter. In an environment where being a heterozygous carrier is rewarded strongly enough, the diseases will propagate–even if they incur a significant cost.
Von Neumann was a child prodigy. When he was 6 years old, he could divide two 8-digit numbers in his head  and could converse in Ancient Greek. When the 6-year-old von Neumann caught his mother staring aimlessly, he asked her, “What are you calculating?”
Children did not begin formal schooling in Hungary until they were ten years of age; governesses taught von Neumann, his brothers and his cousins. Max believed that knowledge of languages in addition to Hungarian was essential, so the children were tutored in English, French, German and Italian. By the age of 8, von Neumann was familiar with differential and integral calculus, but he was particularly interested in history. He read his way through Wilhelm Oncken‘s 46-volume Allgemeine Geschichte in Einzeldarstellungen. A copy was contained in a private library Max purchased. One of the rooms in the apartment was converted into a library and reading room, with bookshelves from ceiling to floor.
Von Neumann entered the Lutheran Fasori Evangélikus Gimnázium in 1911. Wigner was a year ahead of von Neumann at the Lutheran School and soon became his friend. This was one of the best schools in Budapest and was part of a brilliant education system designed for the elite. Under the Hungarian system, children received all their education at the one gymnasium. Despite being run by the Lutheran Church, the school was predominately Jewish in its student body  The school system produced a generation noted for intellectual achievement, which included Theodore von Kármán (b. 1881), George de Hevesy (b. 1885), Leó Szilárd (b. 1898), Dennis Gabor (b. 1900), Eugene Wigner (b. 1902), Edward Teller (b. 1908), and Paul Erdős (b. 1913). Collectively, they were sometimes known as “The Martians“.
One final thing in The 10,000 Year Explosion jumped out at me:
There are also reports of individuals with higher-than-average intelligence who have nonclassic congenital adrenal hyperplasia (CAH)… CAH, which causes increased exposure of the developing fetus to androgens (male sex hormones), is relatively mild compared to diseases like Tay-Sachs. At least seven studies show high IQ in CAH patients, parents, and siblings, ranging from 107 to 113. The gene frequency of CAH among the Ashkenazim is almost 20 percent.
Holy HBD, Batman, that’ll give you a feminist movement.
Heather Booth, Amy Kesselman, Vivian Rothstein and Naomi Weisstein. The names of these bold and influential radical feminists may have faded in recent years, but they remain icons to students of the women’s liberation movement …
The Gang of Four, as they dubbed themselves, were among the founders of Chicago’s Women’s Liberation Union. …
Over weeks, months and years, no subject went unturned, from the political to the sexual to the personal. They were “ready to turn the world upside down,” recalled Weisstein, an influential psychologist, neuroscientist and academic who died in 2015.
But one subject never came up: the Jewish backgrounds of the majority of the group.
“We never talked about it,” Weisstein said.
Betty Friedan was Jewish; Gloria Steinem is half Jewish. There are a lot of Jewish feminists.
Of course, Jews are over-represented in pretty much every intellectual circle. Ayn Rand, Karl Marx, and Noam Chomsky are all Jewish. Einstein and Freud were Jewish. I haven’t seen anything suggesting that Jews are more over-represented in feminism than in any other intellectual circle they’re over-represented in. Perhaps they just like ideas. Someone should come up with some numbers.
Here’s a page on Congenital Adrenal Hyperplasia. The “classic” variety is often deadly, but the non-classic (the sort we are discussing here) doesn’t kill you.
I’ve long suspected that I know so many trans people because some intersex conditions result in smarter brains (in this case, women who are better than average at math.) It looks like I may be on the right track.
Well, that’s the end of the book. I hope you enjoyed it. What did you think? And what should we read next? (I’m thinking of doing Pinker’s Blank Slate.)
Note: this is just a theory, developed in reaction to recent conversations.
As we were discussing Friday, one form of female sociopathy (at least relevant to this conversation) likely involves manipulating or coercing others into providing resources for her children.
There are a couple of obvious tropes:
The evil stepmother, who shunts resources away from a man’s first child, toward his later children.
The cuckoldress, who tricks or convinces a man to care for another man’s children (this is not always seen as evil, since the male drive to provide for children is triggered at least partly by their proximity, since men cannot give birth, and thus men feel genuine affection for children who happen to be around them,)
The crazy ex, who sues a man for all he is worth, doing her best to prevent him from being able to provide for any future children.
How crazy are women?
22%–slightly more than 1 in 5–women have been diagnosed with a mental illness, at least according to all of the data I’ve seen. Since mental illness peaks during the childbearing ages and falls off quickly after menopause, we can also assume that this rate is closer to 1 in 4 during these years.
(The dramatic problems our Native American communities are facing is a separate matter, deserving of its own post.)
The odd thing about this data is that mental illness rates are higher for women than men, despite the fact that mental retardation and mental disability rates are higher for men than women. Men are more likely than women to have serious conditions like non-verbal autism and schizophrenia, more likely to be homeless or commit suicide. When things go terribly wrong, the sufferers are disproportionately male (an unfortunate side effect of the Y chromosome causing greater male variability than female variability on a variety of traits.)
So why on earth do more women than men suffer from mental illness?
Perhaps some forms of mental illness confer some unexpected benefits on women.
Many (perhaps most) “mental illnesses” correlate with a single personality trait–neuroticism:
“Previously we thought that mental illnesses such as depression, schizophrenia, bipolar disorder, and substance abuse, were completely separate diseases,” Ystrøm says.
But research has now shown that these illnesses are often linked. If you suffer from one mental illness, you are more likely to develop another. And if someone in your immediate family has a psychiatric illness, your risk increases not only for this disorder, but for all other disorders.
These findings have led researchers to suspect that there could be a common underlying factor that increases an idividual’s risk of mental illness, overall. …
Ystrøm and colleagues have used new statistical methods to look for patterns in personality, mental disorders, genes, and environmental factors, among the twins in the Twin Register.
And the answer to the question the researchers asked is: yes, neuroticism seems to be the personality trait that best describes the risk of all mental disorders. …
“This one trait doesn’t explain everything. Anyone can develop a mental illness…”
Taking an evolutionary approach, we use data from a contemporary polygynous high-fertility human population living in rural Senegal to investigate whether personality dimensions are associated with key life-history traits in humans, i.e., quantity and quality of offspring. We show that personality dimensions predict reproductive success differently in men and women in such societies and, in women, are associated with a trade-off between offspring quantity and quality. In women, neuroticism positively predicts the number of children, both between and within polygynous families. Furthermore, within the low social class, offspring quality (i.e., child nutritional status) decreases with a woman’s neuroticism, indicating a reproductive trade-off between offspring quantity and quality.
What is neuroticism, in the Big 5 Personality Traits* sense?
*Note: I am not endorsing or denying all five traits one way or another.
It’s worrying. Mothers who worry more about their offspring have more offspring–though it’s quite easy to imagine that the causality points in the opposite direction as the study’s authors conclude–poor women with lots of skinny babies have more reason to worry about their children than women with a few fat babies.
When are women most likely to experience mental illness?
Immediately after the birth of a child. It’s called post-partum depression, and it can be very bad–one woman in my moms’ group ended up in the mental hospital after developing post-partum psychosis. Andrea Yates famously drowned her five children during a bout of post-partum depression/psychosis.
Why on earth would women develop a debilitating mental illness at the most vulnerable time in their offspring’s life? Wouldn’t natural selection select rather quickly against anything that makes women worse at taking care of their offspring?
Let’s turn to everyone’s favorite genetic disease, sickle cell anemia. SCA is famous for being a relatively simple genetic mutation of the sort where if you have one copy of the sickle cell gene, you are less likely to get malaria, and if you have two copies, you tend to die. In areas where malaria is common, the cost of having a quarter of your children die from SCA is lower than the cost of loosing them to malaria.
Personality traits, including neuroticism, generally exist on a continuum. People may become more neurotic when life warrants it, and less neurotic when they don’t need to worry. A mother with a new baby is in a very vulnerable state–she has just lost a good deal of blood, may not be able to walk, and has an infant to care for every other hour, day and night. It is not a normal state by any measure. It is a time when being extra attentive and extra aware of threats and predators is in a woman’s interest.
It is also a time when women are most in need of help from their mates, relatives, or other friends. Increased neuroticism may also prompt others to attend more closely to the new mother, helping her out. . Increased neuroticism may be so helpful during this time period that a few women getting way too much neuroticism and becoming extremely depressed or even killing their children is a cost outweighed by the increased survival of babies whose mothers had moderate levels of neuroticism.
Let us note that nature doesn’t care about your feelings. Male praying mantises who allow themselves be eaten by their mates have more offspring than the ones who don’t, but that doesn’t mean male praying mantises enjoy getting eaten. Children who die of sickle
cell anemia don’t much appreciate that their siblings were protected from malaria, either.
An increase in neuroticism immediately after the birth of a baby may prompt a mother to take better care of it, but that doesn’t mean she enjoys the neuroticism. Neither does it mean that post-partum depression is healthy, any more than sickle cell anemia is healthy just because it’s a side effect of a trait that helps people avoid malaria.
The persistence of common, heritable psychiatric disorders that reduce reproductive fitness is an evolutionary paradox. Here, we investigate the selection pressures on sequence variants that predispose to schizophrenia, autism, bipolar disorder, major depression and attention deficit hyperactivity disorder (ADHD) using genomic data from 150,656 Icelanders, excluding those diagnosed with these psychiatric diseases. … Higher polygenic risk of autism is associated with fewer children and older age at first child whereas higher polygenic risk of ADHD is associated with having more children. We find no evidence for a selective advantage of a high polygenic risk of schizophrenia or bipolar disorder. Rare copy-number variants conferring moderate to high risk of psychiatric illness are associated with having fewer children and are under stronger negative selection pressure than common sequence variants. …
In summary, our results show that common sequence variants conferring risk of autism and ADHD are currently under weak selection in the general population of Iceland. However, rare CNVs that also impact cognition are under stronger selection pressure, consistent with mutation-selection balance. The hypothesis that a selective advantage accounts for the prevalence of sequence variants conferring risk of schizophrenia and bipolar disorder is unproven, but rather this empirical evidence suggests that common sequence variants largely escape selection as their individual effect sizes are weak.
Unfortunately, this study mostly looks at the data in aggregate, instead of breaking it down by males and females. (And I don’t know why they would bother excluding people who actually have the conditions they are trying to study, but perhaps it doesn’t make much difference.)
Thankfully, they did break down the data by male/female in the tables–Table 1 and Table 2. These tables are confusing, but the takeaway is that mental illness has a bigger effect on male fertility than female fertility.
Results Except for women with depression, affected patients had significantly fewer children (FR range for those with psychiatric disorder, 0.23-0.93; P < 10−10). This reduction was consistently greater among men than women, suggesting that male fitness was particularly sensitive. Although sisters of patients with schizophrenia and bipolar disorder had increased fecundity (FR range, 1.02-1.03; P < .01), this was too small on its own to counterbalance the reduced fitness of affected patients. Brothers of patients with schizophrenia and autism showed reduced fecundity (FR range, 0.94-0.97; P < .001). Siblings of patients with depression and substance abuse had significantly increased fecundity (FR range, 1.01-1.05; P < 10−10). In the case of depression, this more than compensated for the lower fecundity of affected individuals.
Conclusions Our results suggest that strong selection exists against schizophrenia, autism, and anorexia nervosa and that these variants may be maintained by new mutations or an as-yet unknown mechanism. Bipolar disorder did not seem to be under strong negative selection. Vulnerability to depression, and perhaps substance abuse, may be preserved by balancing selection, suggesting the involvement of common genetic variants in ways that depend on other genes and on environment.
Now, this study gets interesting in its graphs:
In every case, mental illness has a bigger effect on male fertility than female–and in the case of depression, it has no effect on female fertility.
This graph is confusingly labeled, but it is breaking down the correlation on the brothers and sisters of people with mental disorders. So the first dot represents the brothers of people with schizophrenia; the second dot represents the sisters of people with schizophrenia.
None of these effects are huge, and some of them changed when “comorbidities were included in the analysis,” though it’s not clear exactly what that means–the word comorbidity in this context refers to people with more than one diagnosis.
For the objectives of this study, we first analyzed each disorder separately without accounting for comorbidities. A secondary analysis was then performed that corrected for comorbidities by analyzing all disorders simultaneously.
So when you analyze all of the disorders together, sisters of schizophrenics had no increased fertility, and neither did the siblings of people with bipolar. Depressed men had average fertility, while depressed women actually had slightly above average fertility. The results for anorexia, substance abuse, and autism didn’t change.
Personality variation is increasingly thought to have an adaptive function. This is less clear for personality disorders (PDs)—extreme variants of personality that cause harm in most aspects of life. However, the possibility that PDs may be maintained in the population because of their advantages for fitness has been not convincingly tested. In a sample of 959 outpatients, we examined whether, and how, sexual selection acts on the seven main dimensions of personality pathology, taking into account mating success, reproductive success, and the mediating role of status. We find that, to varying extents, all personality dimensions are under sexual selection. Far from being predominantly purifying, selective forces push traits in diverging, often pathological, directions. These pressures differ moderately between the sexes. Sexual selection largely acts in males through the acquisition of wealth, and through the duration (rather than the number) of mates. This gives a reproductive advantage to males high in persistence–compulsivity. Conversely, because of the decoupling between the number of mates and offspring, the promiscuous strategy of psychopaths is not so successful. Negative emotionality, the most clinically detrimental trait, is slightly deleterious in males but is positively selected in females, which can help to preserve variation.
It’s interesting that the invention of birth control may have inadvertently selected against promiscuous psychopaths–rather similar to the theory that abortion is responsible for the decrease in crime since the early 90s.
“Negative emotionality” is likely equivalent to “neuroticism.”
There are two obvious reasons why mental illness might have more of an effect on males than females–one is that mental illness might simply be mores severe for males than females, on average. The second is that mental illness interferes more with holding down a job than with being a housewife, so women with mental illnesses have more options than men.
Less obvious, though, is that some of these traits might actually be beneficial–in small quantities–for women.
That’s enough for now; let’s continue this discussion on Friday. (Wednesday is book club.)
Note: this is just a theory, developed in reaction to recent conversations.
Let us assume, first of all, that men and women have different optimal reproductive strategies, based on their different anatomy. In case you have not experienced birth yourself, it’s a difference of calories, time, and potential death.
In the ancestral environment (before child support laws, abortion, birth control, or infant formula):
For men, the absolute minimal paternal investment in a child–immediate abandonment–involves a few minutes of effort and spoonful of semen. There are few dangers involved, except for the possibility of other males competing for the same female. A hypothetical man could, with very little strain or extra physical effort, father thousands of children–gay men regularly go through the physical motions of doing just that, and hardly seem exhausted by the effort.
For women, the absolute minimal parental investment is nine months of gestation followed by childbirth. This is calorically expensive, interferes with the mother’s ability to take care of her other children, and could kill her. A woman who tried to maximize her pregnancies from menarchy to menopause might produce 25 children.
If a man abandons his children, there is a decent chance they will still survive, because they can be nursed by their mother; if a woman abandons her child, it is likely to die, because its father cannot lactate and so cannot feed it.
In sum, for men, random procreative acts (ie, sex) are extremely low-cost and still have the potential to produce offspring. For women, random procreative acts are extremely costly. So men have an incentive to spread their sperm around and women have an incentive to be picky about when and with whom they reproduce.
This is well known to, well, everyone.
Now, obviously most men do not abandon their children (nor do most women.) It isn’t in their interest to do so. A man’s children are more likely to survive and do well in life if he invests in them. (In a few societies where paternity is really uncertain, men invest resources in their sisters’ children, who are at least related to them, rather than opting out altogether.) As far as I know, some amount of male input into their children or their sisters’ children is a human universal–the only variation is in how much.
Men want to invest in their children because this helps their children succeed, but a few un-tended bastards here and there are not a major problem. Some of them might even survive.
By contrast, women really don’t want to get saddled with bastards.
We may define sociopathy, informally, as attempting to achieve evolutionary ends by means that harm others in society, eg, stealing. In this case, rape and child abandonment are sociopathic ways of increasing men’s reproductive success at the expense of other people. (Note that sociopathy doesn’t have a formal definition and I am using it here as a tool, not a real diagnosis. If someone has a better term, I’m happy to use it.)
This is, again, quite obvious–everyone knows that men are much more likely than women to be imprisoned for violent acts, rape included. Men are also more likely than women to try to skip out on their child support payments.
Note that this “sociopathy” is not necessarily a mental illness, (a true illness ought to make a dent on one’s evolutionary success.) Genghis Khan raped a lot of women, and it turned out great for his genes. It is simply a reproductive strategy that harms other people.
So what does female sociopathy look like?
It can’t look like male sociopathy, because child abandonment decreases a woman’s fertility. For a woman, violence and abandonment would be signs of true mental defects. Rather, we want to look at ways women improve their chances of reproductive success at the expense of others.
In other words, female sociopathy involves manipulating or coercing others into providing resources for her children.
But it’s getting late; let’s continue with part 2 on Monday. (Wednesday is book club.)
When they compared the DNA of the strain recovered from this cemetery to all published Y. pestis genomes, they found that it was the oldest (most basal) strain of the bacterium ever recovered. Using the molecular clock, they were able to estimate a timeline for the divergence and radiation of Y. pestis strains and tie these events together to make a new, testable model for the emergence and spread of this deadly human pathogen.
These analyses indicate that plague was not first spread across Europe by the massive migrations by the Yamnaya peoples from the central Eurasian steppe (around 4800 years ago)… Rascovan et al. calculated the date of the divergence of Y. pestis strains at between 6,000 and 5,000 years ago. This date implicates the mega-settlements of the Trypillia Culture as a possible origin point of Y. pestis. These mega-settlements, home to an estimated 10,000-20,000 people, were dense concentrations of people during that time period in Europe, with conditions ideal for the development of a pandemic.
The Cucuteni-Trypilia Culture flourished between the Carpathian Mountains and the Black Sea from 4800-3000 BC. It was a neolithic–that is, stone age–farming society with many large cities. Wikipedia gives a confused account of its demise:
According to some proponents of the Kurgan hypothesis of the origin of Proto-Indo-Europeans … the Cucuteni–Trypillia culture was destroyed by force. Arguing from archaeological and linguistic evidence, Gimbutas concluded that the people of the Kurgan culture (a term grouping the Yamnaya culture and its predecessors) … effectively destroyed the Cucuteni–Trypillia culture in a series of invasions undertaken during their expansion to the west. Based on this archaeological evidence Gimbutas saw distinct cultural differences between the patriarchal, warlike Kurgan culture and the more peaceful egalitarian Cucuteni–Trypillia culture, … which finally met extinction in a process visible in the progressing appearance of fortified settlements, hillforts and the graves of warrior-chieftains, as well as in the religious transformation from the matriarchy to patriarchy, in a correlated east–west movement. In this, “the process of Indo-Europeanization was a cultural, not a physical, transformation and must be understood as a military victory in terms of successfully imposing a new administrative system, language, and religion upon the indigenous groups.
How does it follow that the process was a cultural, not physical transformation? They got conquered.
In his 1989 book In Search of the Indo-Europeans, Irish-American archaeologist J. P. Mallory, summarising the three existing theories concerning the end of the Cucuteni–Trypillia culture, mentions that archaeological findings in the region indicate Kurgan (i.e. Yamnaya culture) settlements in the eastern part of the Cucuteni–Trypillia area, co-existing for some time with those of the Cucuteni–Trypillia.Artifacts from both cultures found within each of their respective archaeological settlement sites attest to an open trade in goods for a period, though he points out that the archaeological evidence clearly points to what he termed “a dark age,” its population seeking refuge in every direction except east. He cites evidence of the refugees having used caves, islands and hilltops (abandoning in the process 600–700 settlements) to argue for the possibility of a gradual transformation rather than an armed onslaught bringing about cultural extinction.
How is “refugees hiding in caves” a “gradual transformation?” That sounds more like “people fleeing an invading army.”
The obvious issue with that theory is the limited common historical life-time between the Cucuteni–Trypillia (4800–3000 BC) and the Yamnaya culture (3300–2600 BC); given that the earliest archaeological findings of the Yamnaya culture are located in the Volga–Donbasin, not in the Dniester and Dnieper area where the cultures came in touch, while the Yamnaya culture came to its full extension in the Pontic steppe at the earliest around 3000 BC, the time the Cucuteni–Trypillia culture ended, thus indicating an extremely short survival after coming in contact with the Yamnaya culture.
How is that an issue? How long does Wikipedia think it takes to slaughter a city? It takes a few days. 300 years of contact is plenty for both trade and conquering.
Another contradicting indication is that the kurgans that replaced the traditional horizontal graves in the area now contain human remains of a fairly diversified skeletal type approximately ten centimetres taller on average than the previous population.
What are we even contradicting? Sounds like they got conquered, slaughtered, and replaced.
Then Wikipedia suggests that maybe it was all just caused by the weather (which isn’t a terrible idea.) Drought weakened the agriculturalists and prompted the pastoralists to look for new grasslands for their herds. They invaded the agriculturalists’ areas because they were lush and good for growing grain, which the pastoralists’ cattle love eating. The already weakened agriculturalists couldn’t fight back.
ANYWAY. Lets get on with Greg and Henry’s account, The 10,000 Year Explosion:
The population expansion associated with farming increased crowding, while farming itself made people sedentary. Mountains of garbage and water supplies contaminated with human waste favored the spread of infectious disease. …
Most infectious diseases have a critical community size, a number and concentration of people below which they cannot persist. The classic example is measles, which typically infects children and remains infectious for about ten days, after which the patient has lifelong immunity. In order for measles to survive, the virus that causes it, the paramyxovirus, must continually find unexposed victims–more children. Measles can only persist in a large, dense population: Populations that are too small or too spread out (under half a million in close proximity) fail to produce unexposed children fast enough, so the virus dies out.
Measles, bubonic plague, smallpox: all results of agriculture.
Chickenpox: not so much.
I wonder if people in the old Cucuteni–Trypillia area are particularly immune to bubonic plague, or if the successive waves of invading steppe nomads have done too much genetic replacement (slaughtering) for adaptations to stick around?
Harpending and Cochran then discuss malaria, which has had a big impact on human genomes (eg, sickle cell,) in the areas where malaria is common.
In general, the authors play it safe in the book–pointing to obvious cases of wide-scale genetic changes like sickle cell that are both undoubtable and have no obvious effect on personality or intelligence. It’s only in the chapter on Ashkenazi IQ that they touch on more controversial subjects, and then in a positive manner–it’s pleasant to think, “Why was Einstein so smart?” and less pleasant to think, “Why am I so dumb?”
It’s time to address the old chestnut that biological differences among human populations are “superficial,” only skin-deep. It’s not true: We’re seeing genetically caused differences in all kinds of functions, and every such differences was important enough to cause a significant increase in fitness (number of offspring)–otherwise it wouldn’t have reached high frequency in just a few millennia.
As for skin color, Cochran and Harpending lean on the side of high-latitude lightening having been caused by agriculture, rather than mere sunlight levels:
Interestingly, the sets of changes driving light skin color in China are almost entirely different from those performing a similar function in Europe. …
Many of these changes seem to be quite recent. The mutation that appears to have the greatest effect on skin color among Europeans and neighboring peoples, a variant of SLC24A5, has spread with astonishing speed. Linkage disequilibrium… suggests that it came into existence about 5,800 years ago, but it has a frequency of 99 percent throughout Europe and is found at significant levels in North Africa, East Africa, and as far east as India and Ceylon. If it is indeed that recent, it must have had a huge selective advantage, perhaps as high as 20 percent. It would have spread so rapidly that, over a long lifetime a farmer could have noticed the change in appearance in his village.
In humans, OAC2 … is a gene involved in the melanin pathway… Species of fish trapped in caves… lose their eyesight and become albinos over many generations. … Since we see changes in OCA2 in each [fish] case, however, there must have been some advantage in knocking out OCA2, at least in that underground environment. The advantage cannot like in increased UV absorption, since there’s no sunlight in those caves.
There are hints that knocking out OCA2, or at least reducing its activity, may he advantageous… in humans who can get away with it. We see a pattern that suggests that having one inactive copy of OCA2 is somehow favored even in some quite sunny regions. In southern Africa, a knocked-out version of OCA2 is fairly common: The gene frequency is over 1 percent.
And that’s an area with strong selection for dark skin.
A form of OCA2 albinism is common among the Navajo and other neighboring tribes, with gene frequencies as high as 4.5 percent. The same pattern appears in southern Mexico, eastern Panama, and southern Brazil. All of which suggests that heterozygotes…may ave some advantage.
So why do Europeans have such variety in eye and hair color?
The skeletal record clearly supports the idea that there has been rapid evolutionary change in humans over the past 10,000 years. The human skeleton has become more gracile–more lightly built–though more so in some populations than others. Our jaws have shrunk, our long bones have become lighter, and brow ridges have disappeared in most populations (with the notable exception of Australian Aborigines, who have also changed, but not as much; they still have brow ridges, and their skulls are about twice as thick as those of other peoples.)
This could be related to the high rates of interpersonal violence common in Australia until recently (thicker skulls are harder to break) or a result of interbreeding with Neanderthals and Denisovans. We don’t know what Denisovans looked like, but Neanderthals certainly are noted for their robust skulls.
Skull volume has decreased, apparently in all populations: In Europeans, volume is down about 10 percent from the high point about 20,000 years ago.
This seems like a bad thing. Except for mothers.
Some changes can be seen even over the past 1,000 years. English researchers recently compared skulls from people who died in the Black Death ([approximately] 650 years ago), from the crew of the Mary Rose,a ship that sank in Tudor times ([approximately] 450 years ago) and from our contemporaries. The shape of the skull changed noticeably over that brief period–which is particularly interesting because we know there has been no massive population replacement in England over the past 700 years.
Hasn’t there been a general replacement of the lower classes by the upper classes? I think there was also a massive out-migration of English to other continents in the past five hundred years.
The height of the cranial vault of our contemporaries was about 15 percent larger than that of the earlier populations, and the part of the skull containing the frontal lobes was thus larger.
This is awkwardly phrased–I think the authors want the present tense–“the cranial vault of our contemporaries is…” Nevertheless, it’s an interesting study. (The frontal lobes control things like planning, language, and math.)
We then proceed to the rather depressing Malthus section and the similar “elites massively out-breeding commoners due to war or taxation” section. You’re probably familiar with Genghis Khan by now.
We’ve said that the top dogs usually had higher-than-average fertility, which is true, but there have been important exceptions… The most common mistake must have been living in cities, which have almost always been population sinks, mostly because of infectious disease.
They’re still population sinks. Just look at Singapore. Or Tokyo. Or London.
The case of silphium, a natural contraceptive and abortifacient eaten to extinction during the Classical era, bears an interesting parallel to our own society’s falling fertility rates.
And of course, states domesticate their people:
Farmers don’t benefit from competition between their domesticated animals or plants… Since the elites were in a very real sense raising peasants, just as peasants raised cows, there must have been a tendency for them to cull individuals who were more aggressive than average, which over time would have changed the frequencies of those alleles that induced such aggressiveness.
On the one hand, this is a very logical argument. On the other hand, it seems like people can turn on or off aggression to a certain degree–uber peaceful Japan was rampaging through China only 75 years ago, after all.
Have humans been domesticated?
(Note: the Indians captured by the Puritans during the Pequot War may have refused to endure the yoke, but they did practice agriculture–they raised corn, squash and beans, in typical style. Still, they probably had not endured under organized states for as long as the Puritans.)
There is then a fascinating discussion of the origins of the scientific revolution–an event I am rather fond of.
Although we do not as yet fully understand the true causes of the scientific and industrial revolution, we must now consider the possibility that continuing human evolution contributed to that process. It could explain some of the odd historical patterns that we see.
Well, that’s enough for today. Let’s continue with Chapter 5 next week.
How about you? What are your thoughts on the book?
One of my fine readers asked for “best of” recommendations for Cochran and Harpending’s blog, West Hunter. This is a good question, and as I have not yet found a suitable list, I thought I would make my own.
However, the West Hunter is long, so I’m only doing the first year for now:
Only a handful of Herero shared my skepticism about witchcraft. People in the neighborhood as well as several other employees were concerned about Kozondo’s problem. They told me that he had to be taken to a well known local witch doctor. “Witch doctor” I said, “you all have been watching too many low budget movies. We call them traditional healers these days, not witch doctors”. They all, including Kozondo, would have none of it. “They are bad and very dangerous people, not healers” he said. It quickly became apparent that I was making a fool of myself trying to explain why “traditional healer” was a better way to talk than “witch doctor”. One of our group had some kind of anti-anxiety medicine. We convinced Kozondo to try one but it had no effect at all. Everyone agreed that he must consult the witch doctor so we took him. …
That evening we had something like a seminar with our employees and neighbors about witchcraft. Everyone except the Americans agreed that witchcraft was a terrible problem, that there was danger all around, and that it was vitally important to maintain amicable relations with others and to reject feelings of anger or jealousy in oneself. The way it works is like this: perhaps Greg falls and hurts himself, he knows it must be witchcraft, he discovers that I am seething with jealousy of his facility with words, so it was my witchcraft that made him fall. What is surprising is that I was completely unaware of having witched him so he bears me no ill will. I feel bad about his misfortune and do my best to get rid of my bad feelings because with them I am a danger to friends and family. Among Herero there is no such thing as an accident, there is no such thing as a natural death, witchcraft in some form is behind all of it. Did you have a gastrointestinal upset this morning? Clearly someone slipped some pink potion in the milk. Except for a few atheists there was no disagreement about this. Emotions get projected over vast distances so beware.
Even more interesting to us was the universal understanding that white people were not vulnerable to witchcraft and could neither feel it nor understand it. White people literally lack a crucial sense, or part of the brain. An upside, I was told, was that we did not face the dangers that locals faced. On the other hand our bad feelings could be projected so as good citizens we had to monitor carefully our own “hearts”.
French Canadian researchers have shown that natural selection has noticeably sped up reproduction among the inhabitants of Île aux Coudres, an island in the St. Lawrence River – in less than 150 years. Between 1799 and 1940, the age at which women had their first child dropped from 26 to 22, and analysis shows this is due to genetic change.
… Today the French of Quebec must differ significantly (in those genes that influence this trait) from people in France, which has had relatively slow population growth. …
The same must be the case for old American types whose ancestors – Puritans, for example – arrived early and went through a number of high-fertility generations in colonial days. It’s likely the case for the Mormons, who are largely descended from New Englanders. I’ve heard of odd allele frequencies in CEU (involving FSH) that may relate to this.
Something similar must be true of the Boers as well.
I would guess that a similar process operated among the first Amerindians that managed to get past the ice in North America. America south of the glaciers would have been a piece of cake for anyone tough enough to make a living as a hunter in Beringia – lush beyond belief, animals with no experience of humans.
(Black Russians are, I think, an alcoholic beverage.)
Every now and then, I notice someone, often an anthropologist, saying that human cognitive capability just has to be the same in all populations. According to Loring Brace, “Human cognitive capacity , founded on the ability to learn a language, is of equal survival value to all human groups, and consequently there is no valid reason to expect that there should be average differences in intellectual ability among living human populations. ”
There are a lot of ideas and assumptions in that quote, and as far as I can tell, all of them are wrong. …
Populations vary tremendously in the fraction that contributes original work in science and technology – and that variation mostly agrees with the distribution of IQ.
As I have mentioned before, the mtDNA of European hunter-gathers seems to be very different from that of modern Europeans. The ancient European mtDNA pool was about 80% U5b – today that lineage is typically found at 10% frequency or lower, except in northern Scandinavia. Haplogroup H, currently the most common in Europe, has never been found in early Neolithic or pre-Neolithic Europeans. …
Interestingly, there is a very similar pattern in canine mtDNA. Today Europeans dogs fall into four haplotypes: A (70%), B(16%), C (6%), and D(8%). But back in the day, it seems that the overwhelming majority of dogs (88%) were type C, 12% were in group A, while B and D have not been detected at all.
Richard Lewontin argued that since most (> 85%) genetic variation in humans is within-group, rather than between groups, human populations can’t be very different. Of course, if this argument is valid, it should apply to any genetically determined trait. Thus the variation in skin color within a population should be larger than the skin color differences between populations – except that it’s not. The difference in skin color between Europeans and Pygmies is large, so large that there is no overlap at all.
There is a large region of homogeneity on European haplotypes with the mutation [for lactose tolerance], telling us that it has arisen to high frequency within the last few thousand years. …
In a dairy culture where fresh milk was readily available, children who could drink it obtained about 40% more calories from milk than children who were not LT.
Consider that 1 Liter of cow’s milk has
* 250 Cal from lactose * 300 Cal from fat * 170 Cal from protein
or 720 Calories per liter. But what if one is lactose intolerant? Then no matter whether or not flatulence occurs that person does not get the 250 Calories of lactose from the liter of milk, but only gets 470.
I was contemplating Conan the Barbarian, and remembered the essay that Robert E. Howard wrote about the background of those stories – The Hyborian Age. I think that the flavor of Howard’s pseudo-history is a lot more realistic than the picture of the human past academics preferred over the past few decades. …
Given the chance (sufficient lack of information), American anthropologists assumed that the Mayans were peaceful astronomers. Howard would have assumed that they were just another blood-drenched snake cult: who came closer? …
Most important, Conan, unlike the typical professor, knew what was best in life.
If there is any substantial heritability of merit, where merit is whatever leads to class mobility, then mobility ought to turn classes into hereditary castes surprisingly rapidly.
A start at looking into genetic consequences of meritocracy is to create the simplest possible model and follow its implications. Consider free meritocracy in a two class system, meaning that each generation anyone in the lower class who has greater merit than someone in the upper class immediately swaps class with them. …
Back to the book. Chapter 3: Agriculture: The Big Change
This chapter’s thesis is the crux of the book: agriculture simultaneously exposed humans to new selective pressured and allowed the human population to grow, creating a greater quantity of novel mutations for natural selection to work on.
Sixty thousand years ago, before the expansion out of Africa, there were something like a quarter of a million modern humans. By the Bronze Age, 3,000 years ago that number was roughly 60 million.
Most random mutations fall somewhere between “useless” and “kill you instantly,” but a few, like lactase persistence, are good. I’m just making up numbers, but suppose 1 in 100 people has good, novel mutation. If your group has 100 people in it (per generation), then you get one good mutation. If your group has 1,000 people, then you get 10 good mutations.
Evolution isn’t like getting bitten by a radioactive spider–it can only work on the genetic variation people actually have. More genetic variation=more chances at getting a good gene that helps people survive.
Or to put it another way, we can look at a population and use “time” as one of our dimensions. Imagine a rectangle of people–all of the people in a community, over time–100 people in the first generation, 100 in the second, etc. After enough time, (10 generations or about 200 years,) you will have 1,000 people and of course hit 10 favorable mutations.
Increasing the population per generation simply increases the speed with which you get those 10 good mutations.
One might think that it would take much longer for a favorable mutation to spread through such a large population than it would for one to spread through a population as small as the one that existed in the Old Stone Ag. But sine the frequency of an advantageous allele increases exponentially with time in a well-mixed population, rather like the flu, it takes only twice as long to spread through a population of 100 million as it does to spread through a population of 10,000.
The authors note that larger populations can generate more good, creative ideas, not just genes.
Agriculture–and its attendant high population densities–brought about massive cultural changes to human life, from the simple fact of sedentism (for non-pastoralists) to the ability to store crops for the winter, build long-term housing, and fund governments, which in turn created and enforced laws which further changed how humans lived and interacted.
(Note: “government” pre-dates agriculture, but was rather different when people had no surplus grain to take as taxes.)
Plagues have been kind of a big deal in the history of civilization.
Combined with sedentism, these developments eventually led to the birth of governments, which limited local violence. Presumably, governments did this because it let them extract more resources from their subjects…
Peasants fighting among themselves interferes with the economy. Governments don’t like it and will tend to hang the people involved.
Some people call it self-domestication.
Recent studies have found hundreds of ongoing [genetic] sweeps–sweeps begun thousands of years ago that are still in progress today. Some alleles have gone to fixation, more have intermediate frequencies, and most are regional. Many are very recent: the rate of origination peaks at around 5,000 years ago in the European and Chinese samples, and about 8,500 years ago in the African sample.
I assume that these genes originating about 5,000 years ago are mostly capturing the Indo-European (pastoralist) and Anatolian (farming) expansions. I don’t know what happened in China around 5,000 years ago, but I wouldn’t be surprised if whatever triggered the Indo-Europeans to start moving in central Asia were connected with events further to the east.
IIRC, 8,500 years ago is too early for the Bantu expansion in Africa, so must be related to something else.
There is every reason to think that early farmers developed serious health problems from this low-protein, vitamin -short, high-carbohydrate diet. Infant mortality increased, and the poor diet was likely one of the causes. you can see the mismatch between the genes and the environment in the skeletal evidence Humans who adopted agriculture shrank: average height dropped by almost five inches.
I have seen this claim many times, and still find it incredible. I am still open to the possibility of it having been caused by a third, underlying factor, like “more people surviving diseases that had formerly killed them.”
There are numerous signs of pathology in the bones of early agriculturalists. In the Americas, the introduction of maize led to widespread tooth decay and anemia due to iron deficiency…
Of course, over time, people adapted to their new diets. You are not a hunter-gatherer. (Probably. If you are, hello!)
…Similarly, vitamin D shortages in the new die may have driven the evolution of light skin in Europe and northern Asia. Vitamin D is produced by ultraviolet radiation from the sun acting on our skin… Since there is plenty of vitamin D in fresh meat, hunter-gatherers in Europe may not have suffered from vitamin D shortages and thus may have been able to get by with fairly dark skin. In fact, this must have been the case, since several of the major mutations causing light skin color appear to have originated after the birth of agriculture. vitamin D was not abundant in the new cereal-based diet, and any resulting shortages would have been serious, since they could lead to bone malformations (rickets,) decreased resistance to infectious diseases, and even cancer. …
I have read that of the dark-skinned peoples who have recently moved to Britain, the vegetarians among them have been the hardest-hit by vitamin D deficiency. Meat is protective.
Peoples who have farmed since shortly after the end of the Ice Age (such as the inhabitants of the Middle East) must have adapted most thoroughly to agriculture. In areas where agriculture is younger, such as Europe or China, we’d expect to see fewer adaptive changes… In groups that had remained foragers, there would presumably be no such adaptive changes…
Populations that have never farmed or that haven’t farmed for long, such as the Australian Aborigines and many Amerindians, have characteristic health problems today when exposed to Western diets.
EG, Type 2 diabetes.
Dr. (of dentistry) Weston Price has an interesting book, Nutrition and Physical Degeneration, that describes people Price met around the world, their dental health, and their relationship to Western or traditional diets. (Written/published back in the 1930s.) I’m a fan of the book; I am not a fan of the kind of weird organization that publishes it. That organization promotes fringe stuff like drinking raw milk, but as far as I can recall, I didn’t see anything about drinking raw milk in the entirety of Dr. Price’s tome; Dr. Price wasn’t pushing anything fringe, but found uncontroversial things like “poverty-stricken children during the Great Depression did better in school when given nutritious lunches.” Price was big on improper nutrition as the cause of tooth decay and was concerned about the effects of industrialization and Western diets on people’s bones and teeth.
So we’ve reached the end of Chapter 3. What did you think? Do you agree with Greg and Henry’s model of how Type 2 Diabetes arises, or with the “thrifty genotype” promulgated by James Neel? And why do metabolic syndromes seem to affect poor whites more than affluent ones?
What about the higher rates of FAS among African Americans than the French (despite the French love of alcohol) or the straight up ban on alcohol in many Islamic (ancient farming) cultures? What’s going on there?
Unless I have missed a paper somewhere, this is a remarkable chapter, for The 10,000 Year Explosion was published in 2009, and the first Neanderthal genome showing more overlap with Europeans (and Asians) than Sub-Saharans was published in 2010. Greg and Henry did know of genetic evidence that humans have about 5% admixture from some archaic sister-species, but no one yet had evidence of which species, nor was there popular agreement on the subject. Many scientists still rejected the notion of Sapiens-Neanderthal interbreeding when Cochran and Harpending laid out their bold claim that not only had it happened, but it was a critical moment in human history, jump-starting the cultural cultural effervescence known as behavioral modernity.
Homo sapiens have been around for 300,000 years–give or take a hundred thousand–but for most of that time, we left behind rather few interesting artifacts. As the authors point out, we failed to develop agriculture during the Eemian interglacial (though we managed to develop agriculture at least 7 times, independently, during the current interglacial). Homo sapiens attempted to leave Africa several times before 70,000 years ago, but failed each time, either because they weren’t clever enough to survive in their new environment or couldn’t compete with existing hominins (ie, Neanderthals) in the area.
Sapiens’ technology didn’t do much interesting for the first couple hundred thousand years, either. Yet 70,000 years ago, sapiens did manage to leave Africa, displace the Neanderthals, spread into radically new climates, developed long distance trade and art, and eventually agriculture and everything we now enjoy here in the modern world.
According to Wikipedia, behavioral modernity includes:
Burial, fishing, art, self-decoration via jewelry or pigment, bone tools, sharp blades, hearths, multi-part tools, long-distance transportation of important items, and regionally distinct artifacts.
This leaves two important questions re: Cochran and Harpending’s theory. First, when exactly did behavioral modernity emerge, and second, was it a gradual transition or a sudden explosion?
Prehistoric art is tricky to date–and obviously did not always get preserved–but Blombos Cave, South Africa, currently contains our earliest piece, from about 70,000-100,000 years ago. The Blombos art is not figurative–it’s patterns of crosshatched lines–but there’s a fair amount of it. Blombos appears to have been an ochre-processing spot (the art is made with or on pieces of ochre) littered with thousands of leftover scraps. According to Wikipedia:
In 2008 an ochre processing workshop consisting of two toolkits was uncovered in the 100,000-year-old levels at Blombos Cave, South Africa. Analysis shows that a liquefied pigment-rich mixture was produced and stored in the shells of two Haliotis midae (abalone), and that ochre, bone, charcoal, grindstones and hammer-stones also formed a composite part of the toolkits. As both toolkits were left in situ, and as there are few other archaeological remains in the same layer, it seems the site was used primarily as a workshop and was abandoned shortly after the pigment-rich compounds were made. Dune sand then blew into the cave from the outside, encapsulated the toolkits and by happenstance ensured their preservation before the next occupants arrived, possibly several decades or centuries later.
The application or use of the compound is not self-evident. No resins or wax were detected that might indicate it was an adhesive for hafting.
70 beads made from shells with holes drilled in them have also been found at Blombos.
Blombos is interesting, but the “art” is not actually very good–and we can’t say for sure that it was meant as art at all. Maybe the locals were just scraping the rocks to get the ochre off, for whatever purposes.
Indisputable art emerges a little later, around 40,000 years ago–simultaneously, it appears, in Europe, Asia, Australia, and Indonesia. The archaeology of Africa is less well-documented (in part because things just disintegrate quickly in some areas), but the earliest known sub-Saharan figurative art is about 26,000 years old. This art is both more advanced (it actually looks like art) and more abundant than its predecessors–the Sungir burial, dated to around 30,000-34,000 BC, for example, contains over 13,000 beads–a stark contrast to Blombos’s 70.
If a specific event triggered the simultaneous development of figurative art–and other aspects of behavioral modernity–in four different parts of the world, that event would logically have occurred before those groups split up. The timing of our interbreeding with Neanderthals–“In Eurasia, interbreeding between Neanderthals and Denisovans with modern humans took place several times between about 100,000 and 40,000 years ago, both before and after the recent out-of-Africa migration 70,000 years ago”–is therefore temporaly perfect.
Subsequent back-migration could have then carried the relevant Neanderthal genomesinto Africa–for regardless of where or how behavioral modernity started, all humans now have it.
So what do you think? Did we talk the Neanderthals to death? Did we get the gene for talking from the Neanderthals? Did we out-think them? Or did we just carry some disease or parasite that wiped them out? Or did they wipe themselves out via maternal death in labor, due to their enormous skulls?
(As for FOXP2, it appears that the version found in humans and Neanderthals is slightly different, so I find it a little doubtful that we got it from them.)
A couple of interesting quotes:
In several places, most clearly in central and southwestern France and part of northern Spain, we find a tool tradition that lasted from about 35,000 to 28,000 years ago (the Chatelperronian) that appears to combine some of the techniques of the Neanderthals … with those of modern humans. … Most important, there are several skeletons clearly associated with the Chatelperronian industry, and all are Neanderthal. This strongly suggests that there were interactions between the populations, enough that the Neanderthals learned some useful techniques from modern humans.
The smoking gene?
P. D. Evans and his colleagues at the University of Chicago looked at microcephalin (MCPH1), a very unusual gene that regulates brain size. They found that most people today carry a version that is quite uniform, suggesting that it originated recently. At the same time, it is very different from other, more varied versions found at the same locus in humans today, all of which have many single-nucleotide differences among them. More than that, when there are several different versions of a gene at some locus, we normally find some intermediate versions created by recombination, that is, by chromosomes occasionally breaking and recombining. In the case of the unusual gene (called D for “derived”) at the microcephalin locus, such recombinants are very rare: It is as if the common, highly uniform version of microcephalin simply hasn’t been in the human race all that long in spite of the high frequency of the new version in many human populations. The researchers estimated that it appeared about 37,000 years ago (plus or minus a few tens of thousands of years.) And if it did show up then, Neanderthals are a reasonable, indeed likely, source.
So far as I know (and I looked it up a few weeks ago) no one has yet found microcephalin D in Neanderthals–and the date of 37,000 years ago sounds a bit too recent. However, we haven’t actually genotyped that many Neanderthals (it’s hard to find good 40,000 year old DNA), so we might just not have found it yet–and the date might simply be wrong.
It’s a remarkable genetic finding, even if it didn’t involve Neanderthals–and it might be simpler to dispense with other standards and define Homo sapiens as starting at this point.
On a related note, here’s a bit from Wikipedia about the ASPM gene:
A new allele (version) of ASPM appeared sometime between 14,100 and 500 years ago with a mean estimate of 5,800 years ago. The new allele has a frequency of about 50% in populations of the Middle East and Europe, it is less frequent in East Asia, and has low frequencies among Sub-Saharan African populations. It is also found with an unusually high percentage among the people of Papua New Guinea, with a 59.4% occurrence.
The mean estimated age of the ASPM allele of 5,800 years ago, roughly correlates with the development of written language, spread of agriculture and development of cities. Currently, two alleles of this gene exist: the older (pre-5,800 years ago) and the newer (post-5,800 years ago). About 10% of humans have two copies of the new ASPM allele, while about 50% have two copies of the old allele. The other 40% of humans have one copy of each. Of those with an instance of the new allele, 50% of them are an identical copy. The allele affects genotype over a large (62 kbp) region, a so called selective sweep which signals a rapid spread of a mutation (such as the new ASPM) through the population; this indicates that the mutation is somehow advantageous to the individual.
Testing the IQ of those with and without new ASPM allele has shown no difference in average IQ, providing no evidence to support the notion that the gene increases intelligence. However statistical analysis has shown that the older forms of the gene are found more heavily in populations that speak tonal languages like Chinese or many Sub-Saharan African languages.
For most of he last century, the received wisdom in the social sciences has been that human evolution stopped a long time ago–in the most up-to-date version, before modern humans expanded out of Africa some 50,000 years ago. This implies that human minds must be the same everywhere–the “psychic unity of mankind.” It would certainly make life simpler if it were true.
The book’s main thesis–as you can guess by reading the title–is that human evolution did not halt back in the stone age, but has accelerated since then.
I’ve been reading Greg and Henry’s blog for years (now Greg’s blog, since Henry sadly passed away.) If you’re a fan of the blog, you’ll like the book, but if you follow all of the latest human genetics religiously, you might find the book a bit redundant. Still, it is nice to have many threads tied together in one place–and in Greg & Henry’s entertaining style. (I am about halfway through the book as of this post, and so far, it has held up extremely well over the years since it was published.)
Chapter One: Conventional Wisdom explains some of the background science and history necessary to understand the book. Don’t worry, it’s not complicated (though it probably helps if you’ve seen this before.)
A lot of of our work could be called “genetic history.” … This means that when a state hires foreign mercenaries, we are interested in their numbers, their geographic origin, and the extent to which they settled down and mixed with the local population. We don’t much care whether they won their battles, as long as they survived and bred. …
For an anthropologist it might be important to look at how farmers in a certain region and time period lived; for us, as genetic historians, the interesting thing is how natural selection allowed agriculture to come about to begin with, and how the pressures of an agricultural lifestyle allowed changes in the population’s genetic makeup to take root and spread.
One of the things I find fascinating about humans is that the agricultural revolution happened more or less independently in 11 different places, all around 10,000 years ago. There’s a little variation due to local conditions and we can’t be positive that the Indus Valley didn’t have some influence on Mesopotamia and vice versa, but this is a remarkable convergence. Homo sapiens are estimated to have been around for about 200-300,000 years, (and we were predated by a couple million years of other human ancestor-species like Homo erectus) but for the first 280,000 years or so of our existence no one bothered to invent agriculture. Then in the span of a few thousand years, suddenly it popped up all over the darn place, even in peoples like the Native Americans who were completely isolated from developments over in Asia and Africa.
This suggests to me that some process was going on simultaneously in all of these human populations–a process that probably began back when these groups were united and then progressed at about the same speed, culminating in the adoption of agriculture.
One possibility is simply that humans were hunting the local large game, and about 10,000 years ago, they started running out. An unfortunate climactic event could have pushed people over the edge, reducing them from eating large, meaty animals to scrounging for grass and tubers.
Another possibility is that human migrations–particularly the Out of Africa Event, but even internal African migrations could be sufficient–caused people to become smarter as they encountered new environments, which allowed them to make the cognitive leap from merely gathering food to tending food.
A third possibility, which we will discuss in depth next week, is that interbreeding with Neanderthals and other archaic species introduced new cognitive features to humanity.
And a fourth, related possibility is that humans, for some reason, suddenly developed language and thus the ability to form larger, more complex societies with a division of labor, trade, communication, and eventually agriculture and civilization.
We don’t really know when language evolved, since the process left behind neither bones nor artifacts, but if it happened suddenly (rather than gradually) and within the past 300,000 years or so, I would mark this as the moment Homo sapiens evolved.
While many animals can understand a fair amount of language (dogs, for instance) and some can even speak (parrots,) the full linguistic range of even the most intelligent apes and parrots is still only comparable to a human toddler. The difference between human language abilities and all other animals is stark.
There is great physical variation in modern humans, from Pygmies to Danes, yet we can all talk–even deaf people who have never been taught sign language seek to communicate and invent their own sign language more complex and extensive than that of the most highly trained chimps. Yet if I encountered a group of “humans” that looked just like some of us but fundamentally could not talk, could not communicate or understand language any more than Kanzi the Bonobo, I could not count them members of my species. Language is fundamental.
But just because we can all speak, that does not mean we are all identical in other mental ways–as you well know if you have ever encountered someone who is inexplicably wrong about EVERYTHING here on the internet.
But back to the book:
We intend to make the case that human evolution has accelerated int he past 10,000 years, rather than slowing or stopping, and is now happening about 100 times faster than its long term average over the 6 million years of our existence.
A tall order!
To summarize Cochran and Harpending’s argument: Evolution is static when a species has already achieved a locally-optimal fit with its environment, and the environment is fairly static.
Human environments, however, have not been static for the past 70,000 years or so–they have changed radically. Humans moved from the equator to the polar circle, scattered across deserts and Polynesian islands, adapting to changes in light, temperature, disease, and food along the way.
The authors make a fascinating observation about hunting strategies and body types:
…when humans hunted big game 100,000 years ago, they relied on close-in attacks with thrusting spears. Such attacks were highly dangerous and physically taxing, so in those days, hunters had to be heavily muscled and have thick bones. That kind of body had its disadvantages–if nothing else, it required more food–but on the whole, it was the best solution in that situation. … but new weapons like the atlatl (a spearthrower) and the bow effectively stored muscle-generated energy, which meant that hunters could kill big game without big biceps and robust skeletons. Once that happened, lightly built people, who were better runners and did not need as much food, became competitively superior. The Bushmen of southern Africa…are a small, tough, lean people, less than five feet tall. It seems likely that the tools made the man–the bow begat the Bushmen.
Cro-magnons (now called “European Early Modern Humans” by people who can’t stand a good name,) were of course quite robust, much more so than the gracile Bushmen (Aka San.) Cro-magnons were not unique in their robustness–in fact all of our early human ancestors seem to have been fairly robust, including the species we descended from, such as Homo heidelbergensis and Homo ergaster. (The debate surrounding where the exact lines between human species should be drawn is long and there are no definite answers because we don’t have enough bones.)
We moderns–all of us, not just the Bushmen–significantly less robust than our ancestors. Quoting from a review of Manthropology: The Science of the Inadequate Modern Male:
Twenty thousand years ago six male Australian Aborigines chasing prey left footprints in a muddy lake shore that became fossilized. Analysis of the footprints shows one of them was running at 37 kph (23 mph), only 5 kph slower than Usain Bolt was traveling at when he ran the 100 meters in world record time of 9.69 seconds in Beijing last year. But Bolt had been the recipient of modern training, and had the benefits of spiked running shoes and a rubberized track, whereas the Aboriginal man was running barefoot in soft mud. …
McAllister also presents as evidence of his thesis photographs taken by a German anthropologist early in the twentieth century. The photographs showed Tutsi initiation ceremonies in which young men had to jump their own height in order to be accepted as men. Some of them jumped as high as 2.52 meters, which is higher than the current world record of 2.45 meters. …
Other examples in the book are rowers of the massive trireme warships in ancient Athens who far exceeded the capabilities of modern rowers, Roman soldiers who completed the equivalent of one and a half marathons a day, carrying equipment weighing half their body weight …
McAllister attributes the decline to the more sedentary lifestyle humans have lived since the industrial revolution, which has made modern people less robust than before since machines do so much of the work. …
According to McAllister humans have lost 40 percent of the shafts of the long bones because they are no longer subjected to the kind of muscular loads that were normal before the industrial revolution. Even our elite athletes are not exposed to anywhere near the challenges and loads that were part of everyday life for pre-industrial people.
Long story short: humans are still evolving. We are not static; our bodies do not look like they did 100,000 years ago, 50,000 years ago, nor even 1,000 years ago. The idea that humans could not have undergone significant evolution in 50–100,000 years is simply wrong–dogs evolved from wolves in a shorter time.
Dogs are an interesting case, for despite their wide variety of physical forms, from Chihuahuas to Great Danes, from pugs to huskies, we class them all as dogs because they all behave as dogs. Dogs can interbreed with with wolves and coyotes (and wolves and coyotes with each other,) and huskies look much more like wolves than like beagles, but they still behave like dogs.
The typical border collie can learn a new command after 5 repetitions and responds correctly 95% of the time, whereas a basset hound takes 80-100 repetitions to achieve a 25 percent accuracy rate.
I understand why border collies are smart, but why are bassets so stupid?
Henry and Greg’s main argument depends on two basic facts: First, the speed of evolution–does evolution work fast enough to have caused any significant changes in human populations since we left Africa?
How fast evolution works depends on the pressure, of course. If everyone over 5 feet tall died tomorrow, the next generation of humans would be much shorter than the current one–and so would their children.
The end of the Ice Age also brought about a global rise in sea level. … As the waters rose, some mountains became islands.. These islands were too small to sustain populations of large predators, and in their absence the payoff for being huge disappeared. … Over a mere 5,000 years, elephants shrank dramatically, from an original height of 12 feet to as little as 3 feet. It is worth noting that elephant generations are roughly twenty years long, similar to those of humans.
We have, in fact, many cases of evolution happening over a relatively short period, from dogs to corn to human skin tone.
No one is arguing about the evolution of something major, like a new limb or an extra spleen–just the sorts of small changes to the genome that can have big effects, like the minor genetic differences that spell the difference between a wolf and a poodle.
Second, human populations need to be sufficiently distinct–that is, isolated–for traits to be meaningfully different in different places. Of course, we can see that people look different in different places. This alone is enough to prove the point–people in Japan have been sufficiently isolated from people in Iceland that genetic changes affecting appearance haven’t spread from one population to the other.
What about the claim that “There’s more variation within races than between them”?
This is an interesting, non-intuitive claim. It is true–but it is also true for humans and chimps, dogs and wolves. That is, there is more variation within humans than between humans and chimps–a clue that this factoid may not be very meaningful.
Let’s let the authors explain:
Approximately 85 percent of human genetic variation is within-group rather than between groups, while 15 percent is between groups. … genetic variation is distributed in a similar way in dogs: 70 percent of genetic variation is within-breed, while 30 percent is between-breed. …
Information about the distribution of genetic variation tells you essentially nothing about the size or significance of trait differences. The actual differences we observe in height, weight, strength, speed, skin color, and so on are real: it is not possible to argue them away. …
It turns out that the correlations between these genetic differences matter. … consider malaria resistance in northern Europeans and central Africans. Someone from Nigeria may ave the sickle-cell mutation (a known defense against falciparum malaria,) while hardly anyone from northern Europe does, but even the majority of Nigerians who don’t carry the sickle cell are far more resistant to malaria than any Swede. They have malaria-defense versions of many genes. That is the typical pattern you get from natural selection–correlated changes in a population, change in the same general direction, all a response to the same selection pressure.
In other words: suppose a population splits and goes in two different directions. Population A encounters no malaria, and so develops no malria-resistant genes. Population B encounters malaria and quickly develops a hundred different mutations that all resist malaria. If some members of Population B have the at least some of the null variations found in Population A, then there’s very little variation between Pop A and B–all of Pop A’s variants are in fact found in Pop B. Meanwhile, there’s a great deal of variation within Pop B, which has developed 100 different ways to resist malaria. Yet the genetic differences between those populations is very important, especially if you’re in an area with malaria.
What if the differences between groups is just genetic drift?
Most or all of the alleles that are responsible for obvious differences in appearance between populations–such as the gene variants causing light skin color or blue eyes–have undergone strong selection. In these cases, a “big effect” on fitness means anything from a 2 or 3 percent increase on up. Judging from the rate at which new alleles have increased in frequency, this must be the case for genes that determine skin color (SLC24A5), eye color (HERC2), lactose tolerance (LCT), and dry earwax (ABCC11), of all things.
In fact, modern phenotypes are surprisingly young–blond hair, white skin, and blue eyes all evolved around a mere 10,000 years ago–maybe less. For these traits to have spread as far as they have, so quickly, they either confer some important evolutionary benefit or happen to occur in people who have some other evolutionarily useful trait, like lactose tolerance:
Lactose-tolerant Europeans carry a particular mutation that is only a few thousand years old, and so those Europeans also carry much of the original haplotype. In fact, the shared haplotype around that mutation is over 1 million bases long.
Recent studies have found hundreds of cases of long haplotypeles indicating recent selection: some have reached 100 percent frequency, more have intermediate frequencies, and most are regional. Many are very recent: The rate of origination peaks at around 5,500 years ago in the European and Chinese samples, and at about 8,500 years ago in the African sample.
(Note that the map of blue eyes and the map of lactose tolerance do not exactly correlate–the Baltic is a blue eyes hotspot, but not particularly a lactose hotspot–perhaps because hunter-gatherers hung on longer here by exploiting rich fishing spots.)
Could these explosions at a particular date be the genetic signatures of large conquering events? 5,5000 years ago is about right for the Indo-European expansion (perhaps some similar expansion happened in the East at the same time.) 8,000 years ago seems too early to have contributed to the Bantu Expansion–did someone else conquer west Africa around 8,500 years ago?
Let’s finish up:
Since we have sequenced the chimpanzee genome, we know the size of the genetic difference between chimps and humans. Since we also have decent estimates of the length of time since the two species split, we know the long-term rate of genetic change. The rate of change over the past few thousand years is far greater than this long-term rate over the past few million years, on the order of 100 times greater. …
The ultimate cause of this accelerated evolution was the set of genetic changes that led to an increased ability to innovate. …
Every major innovation led to new selective pressures, which led to more evolutionary change, and the most spectacular of those innovations was the development of agriculture.
Innovation itself has increased dramatically. The Stone Age lasted roughly 3.4 million years (you’ll probably note that this is longer than Homo sapiens has been around.) The most primitive stone tradition, the Oldowan, lasted for nearly 3 million of those 3.4; the next period, the Acheulean, lasted for about 1.5 million years. (There is some overlap in tool traditions.) By contrast, the age of metals–bronze, copper, iron, etc–has been going on for a measly 5,500 years, modern industrial society is only a couple of centuries old–at most.
What triggered this shift from 3 million years of shitty stone tools with nary an innovation in sight to a society that split the atom and put a man on the moon? And once culture was in place, what traits did it select–and what traits are we selecting for right now?
Is the singularity yet to come, or did we hit it 10,000 years ago–or before?
By the way, if you haven’t started the book yet, I encourage you to go ahead–you’ve plenty of time before next week to catch up.