Book Club: The 10,000 Year Explosion, Part 3

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The spread of agriculture

Welcome back to the Book Club. Today we’re reading Chapter 3: Agriculture, from Cochran and Harpending’s The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.

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:

My friend the Witch Doctor:

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”.

Amish Paradise:

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.

Six Black Russians:

(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.

And Your Little Dog, Too!

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.

Lewontin’s Argument 

(always bears re-addressing)

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.

The Indo-European Advantage

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.

The Hyperborean Age

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.

Class, Caste, and Genes: 

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.

Interestingly:

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.)

Agriculture also triggered the spread of plagues, as people now lived in groups large (and often squalid) enough to breed and transmit them. Related: Evidence for the Plague in Neolithic Farmers’ Teeth.

Plagues have been kind of a big deal in the history of civilization.

On government:

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?

And any other thoughts you want to add.

See you next Wednesday for chapter 4.

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Parsis, Travellers, and Human Niches

Irish Travellers, 1954

I.

Why are there many kinds of plants and animals? Why doesn’t the best out-compete, eat, and destroy the others, rising to be the sole dominant species on Earth?

In ecology, a niche is an organism’s specific place within the environment. Some animals eat plants; some eat dung. Some live in the sea; others in trees. Different plants flower and grow in different seasons; some are pollinated by bees and some by flies. Every species has its specific niche.

The Competitive Exclusion Principle (aka Gause’s Law) states that ‘no two species can occupy the same niche’ (or positively, ‘two species coexisting must have different niches.’) For example, if squirrels and chipmunks both want to nest in the treetops and eat nuts, (and there are limited treetops and nuts,) then over time, whichever species is better at finding nuts and controlling the treetops will dominate the niche and the other, less successful species will have to find a new niche.

If squirrels are dominating the treetops and nuts, this leaves plenty of room for rabbits to eat grass and owls to eat squirrels.

II. So I was reading recently about the Parsis and the Travellers. The Parsis, as we discussed on Monday, are Zoroastrians, originally from Persia (modern-day Iran,) who settled in India about a thousand yeas ago. They’re often referred to as the “Jews of India” because they played a similar role in Indian society to that historically played by Jews in Europe.*

*Yes I know there are actual Jews in India.

The Travellers are an Irish group that’s functionally similar to Gypsies, but in fact genetically Irish:

In 2011 an analysis of DNA from 40 Travellers was undertaken at the Royal College of Surgeons in Dublin and the University of Edinburgh. The study provided evidence that Irish Travellers are a distinct Irish ethnic minority, who separated from the settled Irish community at least 1000 years ago; the claim was made that they are as distinct from the settled community as Icelanders are from Norwegians.[36]

It appears that Ireland did not have enough Gypsies of Indian extraction and so had to invent its own.

And though I originally thought that only in jest, why not? Gypsies occupy a particular niche, and if there are Gypsies around, I doubt anyone else is going to out-compete them for that niche. But if there aren’t any, then surely someone else could.

According to Wikipedia, the Travellers traditionally were tinkers, mended tinware (like pots) and acquiring dead/old horses for slaughter.

The Gypsies appear to have been originally itinerant musicians/entertainers, but have also worked as tinkers, smiths, peddlers, miners, and horse traders (today, car salesmen.)

These are not glorious jobs, but they are jobs, and peripatetic people have done them.

Jews (and Parsis, presumably) also filled a social niche, using their network of family/religious ties to other Jews throughout the diaspora as the basis of a high-trust business/trading network at a time when trade was difficult and routes were dangerous.

On the subject of “Madeburg rights” or law in Eastern Europe, Wikipedia notes:

In medieval Poland, Jews were invited along with German merchants to settle in cities as part of the royal city development policy.

Jews and Germans were sometimes competitors in those cities. Jews lived under privileges that they carefully negotiated with the king or emperor. They were not subject to city jurisdiction. These privileges guaranteed that they could maintain communal autonomy, live according to their laws, and be subjected directly to the royal jurisdiction in matters concerning Jews and Christians. One of the provisions granted to Jews was that a Jew could not be made Gewährsmann, that is, he could not be compelled to tell from whom he acquired any object which had been sold or pledged to him and which was found in his possession. Other provisions frequently mentioned were a permission to sell meat to Christians, or employ Christian servants.

External merchants coming into the city were not allowed to trade on their own, but instead forced to sell the goods they had brought into the city to local traders, if any wished to buy them.

Note that this situation is immensely better if you already know the guy you’re selling to inside the city and he’s not inclined to cheat you because you both come from the same small, tight-knit group.

Further:

Under Bolesław III (1102–1139), the Jews, encouraged by the tolerant regime of this ruler, settled throughout Poland, including over the border in Lithuanian territory as far as Kiev.[32] Bolesław III recognized the utility of Jews in the development of the commercial interests of his country. … Mieszko III employed Jews in his mint as engravers and technical supervisors, and the coins minted during that period even bear Hebraic markings.[30] … Jews enjoyed undisturbed peace and prosperity in the many principalities into which the country was then divided; they formed the middle class in a country where the general population consisted of landlords (developing into szlachta, the unique Polish nobility) and peasants, and they were instrumental in promoting the commercial interests of the land.

If you need merchants and goldsmiths, someone will become merchants and goldsmiths. If it’s useful for those merchants and goldsmiths to all be part of one small, close-knit group, then a small, close-knit group is likely to step into that niche and out-compete anyone else trying to occupy it.

The similarity of the Parsis to the Jews probably has less to do with them both being monotheists (after all, Christians, Muslims, and Sikhs are also monotheists,) and more to do with them both being small but widely-flung diasporic communities united by a common religion that allows them to use their group as a source of trustworthy business partners.

Over hundreds or thousands of years, humans might not just move into social niches, but actually become adapted to them–Jew and Parsis are both reported to be very smart, for example.

III. I can think of several other cases of ethnic groups moving into a particular niche. In the US, the gambling and bootleg alcohol trade were long dominated by ethnic Sicilians, while the crack and heroin trades have been dominated by black and Hispanic gangs.

Note that, while these activities are (often) illegal, they are still things that people want to do and the mafia/gangs are basically providing a goods/services to their customers. As they see it, they’re just businessmen. They’re out to make money, not commit random violence.

That said, these guys do commit lots of violence, including murder, blackmail and extortion. Even violent crime can be its own niche, if it pays well enough.

(Ironically, police crackdown on ethnic Sicilian control in NYC coincided with a massive increase in crime–did the mafia, by controlling a particular territory, keep out competing bands of criminals?)

On a more pleasant note, society is now rich enough that many people can make a living as professional sports stars, marry other professional sports stars, and have children who go on to also be professional sports stars. It’s not quite at the level of “a caste of professional athletes genetically optimized for particular sports,” but if this kept up for a few hundred years, it could be.

Similarly, over in Nepal, “Sherpa” isn’t just a job, it’s an ethnic group. Sherpas, due to their high elevation adaptation, have an advantage over the rest of us when it comes to scaling Mt. Everest, and I hear the global mountain-climbing industry pays them well for their services. A Sherpa who can successfully scale Mt. Everest many times, make lots of money, and raise lots of children in an otherwise impoverished nation is thus a successful Sherpa–and contributing to the group’s further genetic and cultural specialization in the “climbing Mt. Everest” niche.

India, of course, is the ultimate case of ethnic groups specializing into specific jobs–it’d be interesting to see what adaptations different groups have acquired over the years.

I also wonder if the caste system is an effective way to minimize competition between groups in a multi-ethnic society, or if it leads to more resentment and instability in the long run.

Chinchillas

Photo credit Melissa Wolf
Photo credit Melissa Wolf (no, it’s not my birthday.)

Chinchillas are probably the cutest of the rodents.

They hail from the desert of the high Andes, where it is simultaneously cold and dry. They are very well adapted to their native habitat, which unfortunately results in them being not very well adapted to places like the US. Some common problems that therefore plague chinchillas kept as pets:

  1. You can’t get them wet. Chinchilla fur is actually so thick and fluffy that it can’t dry out properly on its own, so a wet chinchilla quickly becomes a moldy chinchilla. (Chinchillas take dust baths to get clean.)
  2. They can’t take heat, or even warmth. Our “room temperature” is their “oh god it’s hot.” They prefer to be below 60 degrees F; if the temp heads north of 75, they’ll probably die.
  3. Too many raisins will kill them. Chinchillas love raisins, but unfortunately for them, they’re only adapted to digest dry, brittle, nutrient-poor desert plants. A chinchilla can easily eat a couple of raisins a day without trouble, but if allowed to eat raisins to its heart’s content, its intestines will get all blocked up and the poor creature will die. (At least according to all of the chinchilla-related websites I have read; I have never personally killed a chinchilla.)

(Even though they are cute and fluffy, I don’t get the impression that chinchillas make very good pets, both because they don’t really bond with humans and because they poop constantly. If you really want a rodent, I hear that rats are rather sociable, though honestly, you could just get a dog.)

When I look at modern humans, I can’t help but think of the humble chinchilla, gorging itself to death on raisins. Sometimes we just don’t know what’s bad for us. With us, it’s not just the food–it’s pretty much everything. Find a cute cat picture on the internet? Next thing you know, you’ve just wasted three hours looking at pictures of cats. There are massive internet empires devoted to peoples’ love of looking at a picture of a cat for about two seconds. Sure, you could use that time to interact with a real cat, but that would require getting off your butt.

Facebook is worse than cat pictures. Do you really need to know that your Aunt Susie “likes” IHOP? Or exactly what your Uncle Joe thinks of Obamacare? Or where your vague acquaintance from three years ago had lunch today? No, but you’ll scroll through all of that crap, anyway, rather than face the horrifying prospect of actually interacting with another human being.

I swear, next time I go to a family gathering where people have flown over a thousand miles just to be there, and someone whips out their phone in the middle of a conversation just to check Twitter or FB, I am going to… well actually I will probably just be politely annoyed, but I will definitely be imagining stomping all over that phone.

Modernity is a drug. It tastes great. It’s wonderful. It’s fun. You get TVs and air conditioning and you don’t die of plague. Frankly, it’s awesome. But in the meanwhile, fertility drops. You end up inside, isolated, no longer talking to other humans, simply because that’s more work than clicking on another cake picture. Communities wither. So we get replaced by people who resist modernity, people who still have children and build communities.

Are you here for the long haul? Or are you just here for the raisins?

And if you’re just here for the raisins, why aren’t you enjoying them more?

Hey, DNA: What is it good for?

So why do we still have bits of Neanderthal DNA hanging around after so many years? Of course it could just be random junk, but it’s more fun to think that it might be useful.

And the obvious useful thing for it to do is climate adaptation, since Neanderthals had been living in dark, cold, ice-age Europe for much longer than the newly-arrived h. Sapiens, and so might have had some adaptations to help deal with it.

Okay, so here is something related I was reading the other day, that I consider pretty interesting. So it looks like the people who live up on the Tibetan Plateau (like the Tibetans,) are really well-adapted to the altitude. No mean feat, considering that other populations who live at similar altitudes don’t seem to be as well-adjusted, despite living up there for similar lengths of time.

Well, now it appears that the Tibetans have actually been living in Tibet for waaaay longer than expected, because the original h. Sapiens who moved into Tibet intermarried with archaic hominids who had already lived there for hundreds of thousands of years, and so probably picked up their altitude adaptations from those guys.

BTW, “species” is a social construct and you probably shouldn’t bother with it here.

So what kind of useful stuff might we have picked up from Neanderthals?

First I’d like to interject that I still find declarations of “aha, we got this gene from Neanderthals and it does this!” to be speculative and prone to changing. All of the articles I’ve read tend to report the same list of stuff in a similar fashion, so I suspect they’re all workign off one or two sources, which makes everything doubly sketchy. So we’re going in here with a big “if” this is true…

Some of the results are fairly boring, like Neanderthal DNA affecting hair and skin. We already speculate that skin tone helps us deal with sunlight levels, so that’s sensible.

More interesting is the claim that Neanderthal DNA may predispose people to Type-2 Diabetes and depression.

Now why the hell would it do that? It’s probably not *just* random–after all, large stretches of DNA have little to no Neanderthal admixture at all, suggesting that genes in those spots just weren’t useful, so why would we have retained such apparently negative traits?

Maybe, like sickle cell anemia, these things actually have a positive function–at least in the right environments.

I read a fascinating theory a few years ago that Type 2 Diabetes and Seasonal Affective Disorder are actually just part of our bodies’ natural mechanisms for dealing with winter. Basically, you’re supposed to eat plants and get fat all summer long, while plants are available, and then by winter, your ability to absorb more glucose shuts down (there’s no point since the plants are all dead) and you switch over to burning ketones instead and eating an all-mammoth diet.

(Some groups, like the Inuit and Masai, historically [and may today still] survived on diets that included virtually no plants and so ran all of their cellular energy needs through the ketogenic instead of the glucose system.)

During this winter time, humans, like other animals, slowed down and semi-hibernated to save energy and because why the fuck not, it’s dark and no one has invented lightbulbs, yet.

By spring, you’ve lost a lot of weight, the plants come back, and so does your ability to use glucose.

This theory is laid out in the book Lights Out by T. S. Wiley, if you’re curious. I thought it was a really interesting book, but you might just think it’s all crank, I dunno.

Anyway, a big hole in Wiley’s plot is how we actually got this adaptation in the first place, since it’s a pretty complicated one and h. Sapiens hasn’t actually been living in places with winter for all that long. Wiley just claims that it’s a deep internal mechanism that animals have, which always struck me as kinda bunk because why would a species that evolved in Africa, from other animals in Africa, etc., probably going back for million upon millions of years, have some sort of complicated system like this still functional in its genome? A trait that is not undergoing positive selective pressure is probably going to become non-functional pretty quickly. But the theory was cool enough otherwise to ignore this bit, so I’ve kept it around.

Right, so here’s the (potential) answer: h. Sapiens didn’t have this adaptation hiding deep inside of them, Neanderthals had it. Neanderthals had been living in cold places for way, way longer than h. Sapiens, and by inter-breeding with them, we got to take advantage of a bunch of cold-weather adaptations they’d developed over that time frame–thus getting a jump-start on evolving to cope with the weather.

At any rate, if Wiley is correct, and SAD and Type-2 Diabetes are actually part of a dealing with winter complex that benefited our cold-weather ancestors, then that wold explain why these genes would have persisted over the years instead of being bred out.

An easy way to test this would be to compare rates of Type-2 Diabetes and SAD among African immigrants to Europe/other wintery latitudes, African Americans (who have a small amount of Euro admixture,) and Europeans. (Watching out, of course, for Vit D issues.) If the Euros have more SAD and Type-2 Diabetes than Africans living at the same latitude, then those would appear to be adaptations to the latitude. If the Africans have more, then my theory fails.