Recent Discoveries in Human Evolution: H. Sapiens 300,000 years old?

Welcome back to our discussion of recent exciting advances in our knowledge of human evolution:

  • Ancient hominins in the US?
  • Homo naledi
  • Homo flores
  • Humans evolved in Europe?
  • In two days, first H Sap was pushed back to 260,000 years,
  • then to 300,000 years!
  • Bell beaker paper

As we’ve been discussing for the past couple of weeks, the exact dividing line between “human” and “non-human” isn’t always hard and fast. The very first Homo species, such as Homo habilis, undoubtedly had more in common with its immediate Australopithecine ancestors than with today’s modern humans, 3 million years later, but that doesn’t mean these dividing lines are meaningless. Homo sapiens and Homo neandethalensis, while considered different species, interbred and produced fertile offspring (most non-Africans have 3-5% Neanderthal DNA as a result of these pairings;) by contrast, humans and chimps cannot produce fertile offspring, because humans and chimps have a different number of chromosomes. The genetic distance between the two groups is just too far.

Oldowan tool

The grouping of ancient individuals into Homo or not-Homo, Erectus or Habilis, Sapiens or not, is partly based on physical morphology–what they looked like, how they moved–and partly based on culture, such as the ability to make tools or control fire. While australopithecines made some stone tools (and chimps can make tools out of twigs to retrieve tasty termites from nests,) Homo habilis (“handy man”) was the first to master the art and produce large numbers of more sophisticated tools for different purposes, such as this Oldowan chopper.

But we also group species based on moral or political beliefs–scientists generally believe it would be immoral to say that different modern human groups belong to different species, and so the date when Homo ergaster transforms into Homo sapiens is dependent on the date when the most divergent human groups alive today split apart–no one wants to come up with a finding that will get trumpeted in media as “Scientists Prove Pygmies aren’t Human!” (Pygmies already have enough problems, what with their immediate neighbors actually thinking they aren’t human and using their organs for magic rituals.)

(Of course they would still be Human even if they part of an ancient lineage.)

But if an ecologically-minded space alien arrived on earth back in 1490 and was charged with documenting terrestrial species, it might easily decide–based on morphology, culture, and physical distribution–that there were several different Homo “species” which all deserve to be preserved.

But we are not space aliens, and we have the concerns of our own day.

So when a paper was published last year on archaic admixture in Pygmies and the Pygmy/Bushmen/everyone else split, West Hunter noted the authors used a fast–but discredited–estimate of mutation rate to avoid the claim that Pygmies split off 300,000 years ago, 100,000 years before the emergence of Homo sapiens:

There are a couple of recent papers on introgression from some quite divergent archaic population into Pygmies ( this also looks to be the case with Bushmen). Among other things, one of those papers discussed the time of the split between African farmers (Bantu) and Pygmies, as determined from whole-genome analysis and the mutation rate. They preferred to use the once-fashionable rate of 2.5 x 10-8 per-site per-generation (based on nothing), instead of the new pedigree-based estimate of about 1.2 x 10-8 (based on sequencing parents and child: new stuff in the kid is mutation). The old fast rate indicates that the split between Neanderthals and modern humans is much more recent than the age of early Neanderthal-looking skeletons, while the new slow rate fits the fossil record – so what’s to like about the fast rate? Thing is, using the slow rate, the split time between Pygmies and Bantu is ~300k years ago – long before any archaeological sign of behavioral modernity (however you define it) and well before the first known fossils of AMH (although that shouldn’t bother anyone, considering the raggedness of the fossil record).

This was a good catch. (Here is the relevant Dienekes article, plus Model-based analyses of whole-genome data reveal a complex evolutionary history involving archaic introgression in Central African Pygmies, and Whole-genome sequence analyses of Western Central African Pygmy hunter-gatherers reveal a complex demographic history and identify candidate genes under positive natural selection.) If the slow mutation rate matches the fossil record better than the fast, why use the fast–except if the fast gives you inconvenient results?

But now we have another finding, based on the Bushmen, which also pushes the Bushmen/everyone else split back further than 200,000 years–from BioRxiv, “Ancient genomes from southern Africa pushes modern human divergence beyond 260,000 years ago“:

Southern Africa is consistently placed as one of the potential regions for the evolution of Homo sapiens. To examine the region’s human prehistory prior to the arrival of migrants from East and West Africa or Eurasia in the last 1,700 years, we generated and analyzed genome sequence data from seven ancient individuals from KwaZulu-Natal, South Africa. Three Stone Age hunter-gatherers date to ~2,000 years ago, and we show that they were related to current-day southern San groups such as the Karretjie People. Four Iron Age farmers (300-500 years old) have genetic signatures similar to present day Bantu-speakers. The genome sequence (13x coverage) of a juvenile boy from Ballito Bay, who lived ~2,000 years ago, demonstrates that southern African Stone Age hunter-gatherers were not impacted by recent admixture; however, we estimate that all modern-day Khoekhoe and San groups have been influenced by 9-22% genetic admixture from East African/Eurasian pastoralist groups arriving >1,000 years ago, including the Ju|’hoansi San, previously thought to have very low levels of admixture. Using traditional and new approaches, we estimate the population divergence time between the Ballito Bay boy and other groups to beyond 260,000 years ago.

260,000 years! Looks like West Hunter was correct, and we should be looking at the earlier Pygmy divergence date, too.

Two days later, a paper from the opposite end of Africa appeared in Nature which–potentially–pushes H sapiens’s emergence to 300,000 years ago, “New fossils from Jebel Irhoud, Morocco and the pan-African origin of Homo sapiens“:

Fossil evidence points to an African origin of Homo sapiens from a group called either H. heidelbergensis or H. rhodesiensis. However, the exact place and time of emergence of H. sapiens remain obscure … In particular, it is unclear whether the present day ‘modern’ morphology rapidly emerged approximately 200 thousand years ago (ka) among earlier representatives of H. sapiens1 or evolved gradually over the last 400 thousand years2. Here we report newly discovered human fossils from Jebel Irhoud, Morocco, and interpret the affinities of the hominins from this site with other archaic and recent human groups. We identified a mosaic of features including facial, mandibular and dental morphology that aligns the Jebel Irhoud material with early or recent anatomically modern humans and more primitive neurocranial and endocranial morphology. In combination with an age of 315 ± 34 thousand years (as determined by thermoluminescence dating)3, this evidence makes Jebel Irhoud the oldest and richest African Middle Stone Age hominin site that documents early stages of the H. sapiens clade in which key features of modern morphology were established.

Comparison of the skulls of a Jebel Irhoud human (left) and a modern human (right) (NHM London)

Hublin–one of the study’s coauthors–notes that between 330,000 and 300,000 years ago, the Sahara was green and animals could range freely across it.

While the Moroccan fossils do look like modern H sapiens, they also still look a lot like pre-sapiens, and the matter is still up for debate. Paleoanthropologist Chris Stringer suggests that we should consider all of our ancestors after the Neanderthals split off to be Homo sapiens, which would make our species 500,000 years old. Others would undoubtedly prefer to use a more recent date, arguing that the physical and cultural differences between 500,000 year old humans and today’s people are too large to consider them one species.

According to the Atlantic:

[The Jebel Irhoud] people had very similar faces to today’s humans, albeit with slightly more prominent brows. But the backs of their heads were very different. Our skulls are rounded globes, but theirs were lower on the top and longer at the back. If you saw them face on, they could pass for a modern human. But they turned around, you’d be looking at a skull that’s closer to extinct hominids like Homo erectus. “Today, you wouldn’t be able to find anyone with a braincase that shape,” says Gunz.

Their brains, though already as large as ours, must also have been shaped differently. It seems that the size of the human brain had already been finalized 300,000 years ago, but its structure—and perhaps its abilities—were fine-tuned over the subsequent millennia of evolution.

No matter how we split it, these are exciting days in the field!

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Is Race a Social Construct?

People mean a lot of things when they say “social construct.” Mostly they mean “made up.”

Luckily for us, Google is very helpful:

I may be abusing the word "luckily"

Dear Google and the NY Times: Not only is that not the biological definition of race, it’s not even the biological definition of SPECIES. This is not what laymen mean when they speak of race, not what racists mean when they speak of race, not what blacks or whites or Hindus mean, and definitely not anyone who actually studies human biology and genetics.

The simple folk definition of “race” is “a group of people who look kinda similar and come from the same large area of the world.” This, of course, absolutely exists. Most people in the world look a lot like their neighbors, especially if they live in their ancestral homeland and their country hasn’t been invaded lately.

Now, the exact details of how you racially classify people–are Hindus Caucasian? How about North Africans and Iranians? What about mixed-race people?–are socially constructed. This mean that a word like “black” may mean something different in Russian than it does in the Dominican Republic than it does in the US.

This does not change the underlying reality–the humans referred to as “black” still possess the quality of looking similar to other people from their ancestral part of the world. Reality does not disappear just because people sometimes disagree on exactly how to use words to define it.

The scientific, biological definition of race gets a little more complicated, since it matters whether we are talking abut chromosomal races, fungal races, or humans. A couple of definitions:

Geographical race
A distinct population that is isolated in a particular area from other populations of a species,[9] and consistently distinguishable from the others,[9] e.g. morphology (or even only genetically[4]). Geographic races are allopatric.[7]
Physiological race
A group of individuals that do not necessarily differ in morphology from other members of the species, but have identifiably different physiology or behaviour.[10] A physiological race may be an ecotype, part of a species that is adapted to a different local habitat, defined even by a specific food source.[11]

Notice that neither of these include, “possessing a gene or cluster of genes common to everyone in the race but to no one outside of it.”

But if you don’t like the Wikipedia, here’s what Biology Reference has to say:

The biological definition of race is a geographically isolated breeding population that shares certain characteristics in higher frequencies than other populations of that species, but has not become reproductively isolated from other populations of the same species. (A population is a group of organisms that inhabit the same region and interbreed.) Human racial groups compose a number of breeding units that in the past remained geographically and perhaps temporally isolated, yet could interbreed and produce viable offspring within the species Homo sapiens sapiens.

The Biology-Online Dictionary has some more definitions.
These races are real things, even if biologists disagree about exactly which race a mushroom should belong to.
The reality on the ground:
There are few truly isolated groups in the world, though the Onge (and most likely the Sentinelese) actually fit the NY Times’s wacky definition of a “race” due to thousands of years of isolation on tiny islands in the middle of nowhere:
Click for full size
From Haak et al.
The Onge are the peach stripe between the olive brown section and the purple section.
Major groups in this dataset, running from left to right (excluding the ancient skeletons at the far left):
Light Green: Brazilian rainforest dwellers who may be most closely related to Melanesians
Light Pink: Aztecs and their relatives
Brown: Canadian Indians
Rose: North-East Africans
Dusty Blue: Bantus
Light Blue: Pygmies
Magenta: Tanzanian hunter-gatherers
Orange/Blue/Teal: Europeans
Orange/Purple/Teal: Middle Easterners
Olive Brown: Inuit (Eskimo)
Peach: Onge
Purple: PNG/Australia (Melanesians and Aborigines)
Light Green/Teal: India
Yellow/Red: East Asia
Yellow: Taiwan
Red: Siberia
Some of these groups have very mixed ancestries; people from eastern Canada or the middle of Eurasia, for example. Others are quite distinct–there is no doubt that the Eskimo and Pygmies are genetically distinct, physically distinct, geographically distinct, behave differently, and do not generally marry each other.
We may argue about whether Turks should be considered “Europeans” or “Middle Easterners,” or perhaps say that all orange people should be grouped together, or all teal or blue, but here geography does its job: Europeans look genetically like other Europeans; Indians look genetically like other Indians; Middle Easterners look like each other (except for Bedouins,) etc.
We may also argue about how many races we want to distinguish–people usually determine races based on whichever people are around, but obviously the world is more complicated than this. Americans generally think of “African Americans” as part of a broader race that includes all Africans, but we have distinguished here between 5 different groups, some of which are quite distinct–the ancestors of today’s Pygmies and Bantus, for example, split apart about 100,000 years ago, whereas the ancestors of today’s Bantu’s and Koreans split about 70,000 years ago (as far as we know.) Most African Americans are genetically Bantu (with a bit of European admixture,) not Pygmy. We might in a folk-sense refer to both of these groups as “Africans” or “black,” but genetically (and behaviorally) they are distinct.
Of course, you do not have to call them “races.” Most people studying human genetics use terms like “population,” “ethnic group,” “ethny,” or “clade” instead, but the practical meaning is the same.
But the idea that groups that are genetically, physically, behaviorally, or geographically distinct or distinguishable from each other do not exist is pure nonsense.

Transsexuals Prove That Gender is Real

Don’t stop me if you’ve heard this one: Sex is biological; gender is a social construct.

Well, you should know my response by now: Sex is also a social construct.

X is a social construct does not mean “X is totally made up.” It means, “The word is defined however the hell people feel like using it.” This is true of all language.

200 years ago, people did not define “biological sex” as “has XX or XY chromosomes,” because no one knew about chromosomes, and yet they still had this concept of “biological sex.” For that matter, if you get right down to the nitty gritty of how “biological sex” develops in the fetus/young person, it is not just a matter of “Do you have a Y chromosome?” Biological sex does not work the same for all species, (eg, for crocodiles, the egg’s temperature determines whether the baby inside develops as male or female,) but even within humans, the process is complicated.

Diseases or medical conditions are the easiest way to highlight all the things that come together to determine one’s “biological sex”:

Klinefelter Syndrome: person is born XXY instead of XX or XY. People with KS have tiny genitals. The Y chromosome triggers male development, but the two Xs cause an over-production of female hormones. Most people with KS are infertile. KS occurs in 1:500 to 1:1000 live male births.

Given about 150 million men in the US, that comes out to between 300,000 and 150,000 Americans with Klinefelter Syndrome.

Some other obscure conditions with similar names are XYY, XXXX, and XXYY Syndrome. People with only one X chromosome and nothing else have Turner Syndrome. TS affects about 1 in 2000 to 1 in 5000 females, or about 75,ooo to 30,000 Americans.

Congenital adrenal hyperplasia “are any of several autosomal recessive diseases resulting from mutations of genes for enzymes mediating the biochemical steps of production of cortisol from cholesterol by the adrenal glands (steroidogenesis).

“Most of these conditions involve excessive or deficient production of sex steroids and can alter development of primary or secondary sex characteristics in some affected infants, children, or adults.”

The Wikipedia  recounts the potential first historical description of a CAH case:

“‘In one of the anatomical theaters of the hospital…, there arrived toward the end of January a cadaver which in life was the body of a certain Joseph Marzo… The general physiognomy was decidedly male in all respects. There were no feminine curves to the body. There was a heavy beard. There was some delicacy of structure with muscles that were not very well developed… The distribution of pubic hair was typical of the male. Perhaps the lower extremities were somewhat delicate, resembling the female, and were covered with hair… The penis was curved posteriorly and measured 6 cm, or with stretching, 10 cm. The corona was 3 cm long and 8 cm in circumference. There was an ample prepuce. There was a first grade hypospadias… There were two folds of skin coming from the top of the penis and encircling it on either side. These were somewhat loose and resembled labia majora.’

“De Crecchio then described the internal organs, which included a normal vagina, uterus, tubes, and ovaries. … He interviewed many people and satisfied himself that Joseph Marzo “conducted himself within the sexual area exclusively as a male”, even to the point of contracting the “French disease” on two occasions. “

CAH apparently varies in incidence; among the American Indians, 1 in 280; among whites, 1 in 15,000. Given 245.5 million whites and 3 million Indians, that works out to about 27,000 in those two groups. (Wikipedia doesn’t give numbers for blacks or Hispanics.)

Androgen insensitivity syndrome “is a condition that results in the partial or complete inability of the cell to respond to androgens. The unresponsiveness of the cell to the presence of androgenic hormones can impair or prevent the masculinization of male genitalia in the developing fetus, as well as the development of male secondary sexual characteristics at puberty, … these individuals range from a normal male habitus with mild spermatogenic defect or reduced secondary terminal hair, to a full female habitus, despite the presence of a Y-chromosome.”

The people in this picture have XY chromosomes, but developed as females because they have have AIS or related conditions:

1280px-Orchids01

The exact incidence is unknown, especially since XX carriers are basically unaffected by the condition, but Wikipedia lists estimates between 1 in 20,400 XY births and one in 130,000, or between about 7,000 and 1,000 affected Americans.

Kallman Syndrome isn’t so much an “intersex” disorder as an “asex” disorder. Kallmann syndrome is a genetic disorder in which, “the hypothalamic neurons that are responsible for releasing gonadotropin-releasing hormone (GnRH neurons) fail to migrate into the hypothalamus during embryonic development.”

The most prominent symptom is a failure to start puberty; oddly, one of the other common symptoms is an inability to smell. It affects both men and women.

Incidence: about 1 in 10,000, or about 32,000 Americans.

True hermaphrodites” are rare, but do exist–perhaps due to improper cell division in developing fraternal twins. See also “human chimeras“:

“The Dutch sprinter Foekje Dillema was expelled from the 1950 national team after she refused a mandatory sex test in July 1950; later investigations revealed a Y-chromosome in her body cells, and the analysis showed that she probably was a 46,XX/46,XY mosaic female. …

“Another report of a human chimera was published in 1998, where a male human had some partially developed female organs due to chimerism. He had been conceived by in-vitro fertilization.

“In 2002, Lydia Fairchild was denied public assistance in Washington state when DNA evidence showed that she was not related to her children. A lawyer for the prosecution heard of a human chimera in New England, Karen Keegan, and suggested the possibility to the defense, who were able to show that Fairchild, too, was a chimera with two sets of DNA.”

And as I have mentioned before, people exposed to Diethylstilbestrol–DES–a synthetic estrogen used as an anti-miscarriage drug between 1940 and 1971, (when they realized its major epigenetic effects included cancer,) seems to have triggered female brain development in male fetuses.

“An estimated 3 million pregnant women in the USA were prescribed DES from 1941 through 1971. … The number of persons exposed to DES during pregnancy or in utero during 1940–1971 is unknown, but may be as high as 2 million in the United States.” Or about 1 million men.

There are others, but I will stop here. It is difficult to give a total for such conditions, but folks estimate incidence of intersex conditions around 1.7% of births, or 5.4 million Americans. (By contrast, identical twins occur in only 0.3% of pregnancies.)

As I have mentioned before, I strongly suspect that the vast majority of “trans” people actually have some form of intersex condition–I base this suspicion on the lives of the trans  people I’ve actually talked to. According to LiveScience, about 700,000 Americans, or 0.2%, are trans–significantly less than the estimated number of people with intersex conditions.

Even though 98.3% of us probably don’t have any kind of intersex (or asex) condition, 5.4 million is a lot of people. In a country where we like to put weirdos on TV so we can laugh and point at them, really obscure conditions can become quite well-known. Like octuplets.

Whether you want to call them “male,” “female,” “intersex,” or something else all has to do with your particular definition of “biological sex.” If you’d lived in 1800, your definition of “biological sex” would probably have something to do with genitals and maybe something to do with behavior, but certainly nothing to do with chromosomes or hormones or anything like that. Ten minutes ago, you probably defined “biological sex” as “has XX or XY chromosomes.” Now you’re probably wondering what the hell is up with crocodiles.

None of this changes reality. Reality doesn’t care what you call it.

 

On to Gender!

What does it mean when people say, “Gender is a social construct”?

I’m pretty sure the technical answer is, “Gender is the set of behaviors and social roles and things that people expect out of people based on their biological sex, and those expectations vary by society, ie, people in Uganda expect different things out of ‘men’ and ‘women’ than people in Japan. Heck, some societies even have ‘third genders’ and things like that.”

However, most of the time when people say, “Gender is a social construct,” what they actually mean is, “People don’t actually have gender; gender roles are a mass delusion created by the Patriarchy to oppress women that we are taught to hallucinate as little kids.”

Unfortunately, the belief that children are blank gender slates is not only common among many academics and feminists, but was a thing people really believed–leading to the surgical “correction” of intersex children born with incorrect genitalia, followed by attempts at raising them as whatever gender the parents picked. They usually picked female, because it is much easier to lop a bit off than to add on.

Imagine, for a moment, that you born with a small penis, so your parents just decided to have it chopped off, turned the nub into a clitoris, stuck a dress on you, and called you a girl.

No, it doesn’t work.

I don’t have any statistics, but I have read a lot of stories along the lines of, “My parents lied to me all my life that I was a girl and it turned out I was a boy and it was horribly traumatic and I was suicidal for most of puberty, etc., etc.”

Gender is a real thing, and even intersex kids can figure it out.

If the feminist “You learn gender roles from the patriarchical society around you” school of thought were correct, these kids would turn out completely normal members of the gender assigned to them and not have any issues at all.

If gender is a real thing, then trying to raise a kid as the opposite gender should result in exactly what we see: The kids are miserable, and then they assert that they are the gender they were born as.

 

But what about trans people who don’t have any kind of intersex condition? Given 7 billion people in the world, there are probably some. Again, if gender were nothing more than arbitrary social roles determined by our dumb patriarchical society, why would anyone bother changing their “sex” to match their “gender”? Remember that SRS is very expensive, painful, time consuming, and incurs significant social stigma. If I can just say, “hey, all this business with handbags and football is totally arbitrary; I’m just going to re-define football as a thing “women” like and handbags as something “men” like,”–which is exactly what the feminist theory of gender claims you can do–then why wouldn’t trans people just do that, and save themselves all of the effort?

Because trans people understand that gender is a real thing, not just a made up thing that they can re-define because it happens to suit them.

“But wait,” I hear you saying, “trans people are actually just autogynophiliacs, and so that’s why they transition, not because they’re actually trans.”

To be honest, I consider this a weird story. For starters, half the trans people I know started as “female”, not male. Second, almost all of the trans people I know have really obvious intersex conditions. Third, most people into LGBTQ etc. sorts of things will NOT SHUT UP about their sexual interests. If these people had weird self-fetishes, they’d be talking about it all over the damn place. Like furries. Remember furries? No one was ever confused about furries’ sexual interests.

Now, could some trans people be autogynophiliacs? Sure. There are 700,000 of them in the country. That’s a lot of people. Some of ’em are probably into all kinds of weird things.

But there are about 1 million men who were exposed to DES in the womb. So DES sounds like a more likely cause of biological men who “feel female” than weird sexual fetishes.

However, I am willing to grant a chicken and egg potential: once a “man” starts believing that he really is a woman trapped in a man’s body, then he will of course begin thinking about himself as female, and want other people to treat him as female, and even fantasize about being treated like a normal female, being found attractive as a normal female, etc.

That is, I suspect the autogynophiliac hypothesis has the causation backwards. Believing that one is a female trapped in a man’s body leads to imagining oneself as female, not the other way around. The same probably holds true for trans folks in “female” bodies who decide that they are really men–they desire to be seen as attractive, too.

(I will note that a fair number of people with intersex conditions are asexual.)

Now, does that mean that Jenner or any other high-profile celebrity trans person is actually intersex and not just a weird attention whore? I have no clue, but if Jenner wants to be female, I don’t care.

But I don’t consider Jenner “brave” or “pioneering” or anything like that. Jenner has millions of dollars and a media three-ring circus to praise her every move. Meanwhile, I know people with actual, diagnosed chromosomal abnormalities who live in poverty because their families don’t believe in fucking genetics.

 

But anyway, why does this whole “Sex != Gender” thing get hauled out every time people start trying to explain transsexuals?

Eh, it’s because they’re gender non-conforming weirdos and so for a long time, the only people who would accept them were other gender non-conformists like radical feminists and gay people, and this whole “gender is a social construct” business has been the dominant catch-phrase of feminists out to re-define femininity for a long time. And I’m sure that for some trans people, it has given them some peace of mind to think that it’s okay, they can redefine gender how they want to include people like themselves.

But that doesn’t change the fact that the reality of gender is what trans people are actually seeking.