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As a backdrop to the specifics that follow: humans and human cousins have been sort of ambling out of Africa and back in waves of migration and interbreeding and extinction, for the past two million years.

Around 650K years ago, humans split from the group that will further split 200K years later into Neanderthals and Denisovans. These are the two 'archaic human' populations that contributed some genetic material to modern humans, whose DNA we got our hands on. This is also maybe the divergence point of humans and another archaic population in Africa that later mixed back into humans, that we don’t have DNA evidence for.

200K years ago, zoom in on the ambling in and out of Africa, because now some of the ambling groups are what we’d call anatomically modern humans – that is, their phenotypes fit within existing human populations. At this point, the split between the San population (the most different-from-everyone-else population alive today, whose descendants currently live in South Africa) and the rest of living humanity begins.

50K years ago, a period of great interest. We see behavioral modernity starting hereish, at the beginning of a period (lasting ~40K years) we call the Upper Paleolithic. The rate of stone toolmaking innovation speeds up from ‘glacial’ to ‘every few thousand years’. (If that seem like an odd setting change, I agree.) We see the first known jewelry and representational art. Likely we’ll never have a satisfactory explanation of what exactly changed. We almost certainly had language by this point.

Human colonization of Australia and New Guinea happens, while ocean levels are low. This is part of a radiation of a hunter-gatherer lineage spreading out all over Asia. Some of them will eventually go to Siberia and the Americas. Some of them will become the Yangtze River population and some the Yellow River population, who will later mix to produce the majority of mainland East Asians.

40K years ago. After several thousands of years of contact with modern humans, Neanderthals and some other branches more closely related to modern humans go extinct. There’s an Italian supervolcano eruption nowabouts whose climate disruptions in Europe may have intensified competition.

One thing this book has taught me is that it’s misleading to talk about ‘population splits’ outside of the Americas, because lineages diverged and met again many times, but insofar as it’s meaningful to talk about when the European and East Asian lineages diverged, it’s now.

30K years ago. The archaic humans in Africa mix back with humans and contribute 2% of ancestry to some modern African populations.

Around this time, there exists a population called Ancient North Eurasians. Some of them go east, and contribute to the population that will give rise to Native Americans (who are ~1/3 Ancient North Eurasian, ~2/3 ancestors-of-East-Asians). Some of the rest will remain and contribute ancestry to various Eurasian hunter gatherers, as well half the ancestry of the Yamnaya people of the Eurasian steppe, who will later invent horse-and-wagon way of life and become massively successful in Europe.

15K years ago, there are two migrations to America over the Bering land bridge: (1) The First Americans (the Ancient North Eurasian - East Asian group) account for the majority of Native American ancestry. These newcomers quickly zoom through the Americas. They also may have had a startlingly small effective population size – like 250. (2) A mysterious population that contributes some ancestry to a handful of groups in the Amazon, a population whose closest known descendants today are, intriguingly, Australasian. We don’t know much about them.

10K years ago, agriculture arises in the Middle East. Some Anatolian farmers spread out into Europe. Some Iranian farmers spread out to India. A thousand years later, agriculture also begins in China, in the Yangtze River and Yellow River populations.

5K years ago. The horse-and-wagon Yamnaya sweep from the eastern European steppe into northern Europe and largely replace the population there, and account for 25~45% of current European ancestry. The Yamnaya culture is the strongest candidate for the source of the Proto-Indo-European language (which has an elaborate shared vocabulary for wagon-parts). A large part of their success may have been that they were relatively immune to diseases that the rest of Europe was not – they brought plague with them, heretofore unknown to Europe. With the Yamnaya, the Bronze Age; we have evidence of much more social inequality than ever seen before, evident both from archeology and genetics, which tell us that the highest-reproducing individual men starting now are more reproductively successful than ever before.

Around the same time, there’s another wave of migration from Asia to North America – the Paleo-Eskimo lineage – that leaves a ~30% imprint in some parts of North America. The Paleo-Eskimos will be displaced 4K years later by a final wave from Asia, the Neo-Eskimos, who are the ancestors of modern day Inuits.

The Yangtze and Yellow River populations are also spreading out nowish. Their collision produces much of modern East Asians. The Yellow River people are associated with the Han, and the Tibetans. The Yangtze population, where they spread south, provides much of modern Southeast Asian ancestry.

4K years ago, the Indus Valley civilization is hit by a wave of migration for Europeish, by a steppe people who bring Proto-Indo-European culture and language. These steppe people are about half Yamnaya-related, and half ‘the Iranian farmer related populations the steppe people encountered on their way south’. The natives are about three quarters local hunter-gatherers, and one quarter Iranian farmers who mingled in ~2K years earlier. The natives and Yamnaya-ish migrants mix over the next 2K years to form a modern Indian population that’s a mixture of the two, ranging from 80% Yamnaya-ish (especially in the north, and in higher-caste groups) to 20%.

So, the core charm of the original PWP is that there is the protagonist is subjected to some extreme, kinkmeme-unrealistic, workplace sexual harassment (eating out her boss is part of the job) but immediately turns the tables, at least in the interpersonal dynamic, and starts domming the heck out of her boss. The pubfic gets rid of this conceit and is much worse for it. The characters strongly hold the socially correct ideas on what the boundaries of a workplace relationship are and never get near anything morally iffy. And... I don’t know, I really want some morally iffy, ordinarily horrible lesbians. I crave! (Go embezzle some money, or raise tigers in your home, or something!) Here’s an excerpt from the fanfic that counts among my favorite ever characterization work:

I look down at the advertisement for Tommy Hilfiger that's laid out on my desk. A woman leans back against a man on the roof of a car, out in the middle of a desert. I briefly study the ad, and then close my eyes. Her body is long and lean and tanned; her hair is dirty blonde; she's wearing a bandanna and a loose white blouse. I couldn't say what the man looked like if somebody held a gun to my head.

Dear God. I'm a lesbian. I'm fifty years old, and I've just now figured out that I'm gay. The realization provokes any number of feelings in me: mortification, that I've been so slow on the uptake; a sense of relief, that something's fallen into place at last; and finally, a real kind of fury, because even if I've figured this out I still don't want to be a lesbian. I want to be happily married to my husband. This is extraordinarily inconvenient. How dare the universe do this to me?

More than that, I've seen lesbians. Oftentimes, they've been denouncing me personally, accusing me of distorting images of womanhood, of making women lose weight and shrink until they're about to disappear. Of hating women. I've seen them on television, and in magazines and newspapers, and sometimes picketing across the street from Elias-Clarke until Irv found some way to get rid of them. They're ridiculous. More often than not they were overweight, and had horrible haircuts, and the ugliest shoes I've ever seen, and apparently had never heard of either makeup or supportive undergarments. They carried signs and placards with words like "womyn" on them. They'd rather burn me in effigy than have me as one of their number. I'd prefer that, too. And I certainly don't want to have sex with any of them.

The narrator above has ten times more personality than their pubfic version (who sort of simplistically resists being gay for most of the novel for reasons): she is having an actually interesting, enormously self-centered, particular experience of realizing she’s queer and has some latent ‘relationship with queerness’, a particular experience that is indispensably conditioned on the fact that she is an asshole.

The dissatisfaction I’m feeling isn’t about the novel per se. I have general disappointment about queer lit that stems from, I think, the state of the world where... queer romance novels take on this double duty of (1) representing/articulating queer experiences, including romantic experiences, and (2) being an object of pleasurable consumption for your average horny reader. And your horny reader may want things like ‘Miranda Priestly gets railed by her personal assistant whom, until last week, she didn’t really consider a full human being’, which fails duty (1), so it gets cut and you end up with the blandest stuff about decent human beings who like each other and like having sex.

I suspect this effect is especially pronounced in f/f because writers and readers of romance fiction in general skew female, so any queer woman writing f/f is generally writing it for other queer women, which adds the pressure of – oh, this is about us. This is about our community, our experiences and identities. Shape up!

(I’m going to go with the handy convention that the primary ancestor group of modern humans are called ‘humans’ and other branches aren’t, but I very much think of Neanderthals as a subset of humans.)

One of the most interesting things I got from Who We Are and How We Got Here was more information on Neanderthal-human hybridization. I knew the common factoid that that non-Africans have about 2% Neanderthal ancestry, that this mixture had happened about 40K years ago when humans expanded into Europe, and that Neanderthals went extinct several thousand years afterwards.

Zooming in on that 2% –

The average proportion of Neanderthal ancestry in non-African populations is about 2 percent, but it is not spread evenly. In more than half the genome, no Neanderthal ancestry has been detected in anyone. But in some unusual places in the genome, more than 50 percent of DNA sequences are from Neanderthals.

Where do we see selection against Neanderthal ancestry? In parts of the genome known to be relevant to the fertility of hybrids.

One is the X chromosome, which apparently is a default site of selection-against-minority-ancestry in hybrids:

How is it that hybridization can lead to so much less genetic variation on chromosome X than on the rest of the genome? From studies of a variety of species across the animal kingdom, it is known that when two populations are separated for long enough, hybrid offspring have reduced fertility. In mammals like us, reduced fertility is much more common in males, and the genetic factors contributing to this reduced fertility are concentrated on chromosome X. So when two populations are so separated that their offspring have reduced fertility, but nevertheless mix together to produce hybrids, it is expected that there will be intense natural selection to remove the factors contributing to reduced fertility. This process will be especially evident on chromosome X because of the concentration of genes contributing to infertility on it. As a result, there tends to be natural selection on chromosome X for stretches of DNA from the population that contributed most of the hybrid population’s ancestry. This causes the hybrid population to derive its chromosome X almost entirely from the majority population, leading to an anomalously low genetic divergence on chromosome X between the hybrid population and one of the hybridizing populations, consistent with the pattern seen in humans and chimpanzees.

Another relevant area where Neanderthal ancestry was selected are genes responsible for the male reproductive tissue. Apparently they’re finicky. Genes that are active in the germ cells of testicles have less Neanderthal ancestry on average than genes that are most active in other body tissues.

These aren’t the only parts of the genome where Neanderthal ancestry was selected against, just the sites of strongest selection. Neanderthal genes have been selected against around the majority of genes – there is far more Neanderthal ancestry in noncoding DNA than in coding. The book has this striking visualization of the decline. Neanderthal ancestry in humans was closer to 3~6 percent when hybridization occurred in Europe.

Hybrids were only kind of working out, fertility-wise; Neanderthals and humans must have been on the brink of speciation at the time they met.

Just as interesting as “what was selected against”, if not more: Where do we see selection for Neanderthal ancestry? Skin and hair!

Interbreeding with Neanderthals helped modern humans to adapt to new environments just as interbreeding with Denisovans did. We and others showed that at genes associated with the biology of keratin proteins, present-day Europeans and East Asians have inherited much more Neanderthal ancestry on average than is the case for most other groups of genes. This suggests that versions of keratin biology genes carried by Neanderthals were preserved in non-Africans by the pressures of natural selection, perhaps because keratin is an essential ingredient of skin and hair, which are important for providing protection from the elements in cold environments such as the ones that modern humans were moving into and to which Neanderthals were already adapted.

Other neat Neanderthal facts I’m shoehorning in:

- They were less genetically diverse than humans (book says ‘the diversity of their genomes was about four times smaller’, but I’m not sure what figure actually represents) – this may have been a problem for them that contributed to their extinction, because low-genetic-diversity populations tend to stack up more detrimental mutations.

- Neanderthal-human mixing happened in Europe, but the current day group with the most Neanderthal ancestry is East Asians. This is probably because humans mixed with Neanderthals, spread out over Eurasia, and then Europe had another influx of non-Neanderthal human expansion that contributed to the current-day European gene pool and diluted Neanderthal ancestry.

The fusion of these highly different populations into today’s West Eurasians is vividly evident in what might be considered the classic northern European look: blue eyes, light skin, and blond hair. Analysis of ancient DNA data shows that western European hunter-gatherers around eight thousand years ago had blue eyes but dark skin and dark hair, a combination that is rare today. [33] The first farmers of Europe mostly had light skin but dark hair and brown eyes—thus light skin in Europe largely owes its origins to migrating farmers. [34] The earliest known example of the classic European blond hair mutation is in an Ancient North Eurasian from the Lake Baikal region of eastern Siberia from seventeen thousand years ago.

33: I. Olalde et al - "Derived Immune and Ancestral Pigmentation Alleles in a 7,000-Year-Old Mesolithic European," Nature 507 (2014):225-28.