Category: human evolution

Did humans occupy the New World over 30,000 years ago? New paper suggests it.

July 23, 2020 • 9:45 am

This new paper in Nature (click on screenshot, pdf here, reference at bottom) has the potential to be the big human-paleobiology story of the last several years.  It reports finding human occupancy of a high-altitude cave in Mexico during the last glacial maximum (LGM): about 26,000 years ago.  And that, say the authors, implies that humans have been in the New World since more than 30,000 years ago—more than doubling the time we thought they’d been here. Previously, the best guess was that humans crossed the Bering Strait from Siberia about 15,000 years ago, and then spread through the Americas.

Click on the screenshot below to get the paper (free through the legal app Unpaywall, or you can make a judicious inquiry).

Before we accept these results as overturning the received wisdom about humans in the New World, though, there has been some criticism of the paper, as you can see in a precis in Science by Andrew Curry.

The cave where the finds were made sits atoop a remote mountain in the Mexican state of Zacatecas, about 2,740 m high, and has been studied since 2012.  Although dry and barren now, it was thought to be verdant during the LGM, with water, plants, and plenty of edible animals nearby.  Researchers worked there for a month at a time, camping in the cave and hauling water and food by donkey from the nearest town.

What made the researchers suppose that the cave was occupied by humans were several things, most prominently 2000 specimens of what looked like sculpted tools. Here’s a figure showing some of these putatively manufactured objects:

(from paper): a, Core. b–e, Flakes; inlay in b emphasizes an isolated platform. f–j, Blades. k–o, Points. Scale bar, 3 cm. Most items are from component SC-B; d and m belong to SC-C. One Pseudotsuga sp. (Douglas fir) charcoal fragment closely associated with the bifacial preform shown in m in stratum 1223 was dated to 27,929 ± 82 uncalibrated radiocarbon years BP (PRI-5414). More lithic finds are shown in Extended Data Figs. 5, 6.

 

Now I would have thought that by now paleoanthropologists would be able to distinguish non-human rock artifacts from real, chipped tools, but apparently that’s not the case. As one critic says in the Science writeup:

Critics point out that the tools are simple and don’t resemble other toolkits from the Americas, raising the possibility they’re the product of natural breakage. “They look like they could be artifacts, but why aren’t they found anywhere else in the landscape?” wonders David Meltzer, an archaeologist at Southern Methodist University. The tools’ consistency is also remarkable, he says. “If these tools are real, why are they only found—so far at least—in this one spot over a 10,000-year period? Humans adapt and adopt new technology.”

The tool-making conclusion, at least, must remain tentative. There was also burned wood that was radiocarbon dated, implying human campfires, but the critics again say that this could derive be from “wind-blown” wildfires. The researchers also used OSL dating of quartz from the sediments, which tells you when the mineral was last exposed to light, ergo when it was laid down.

Finally, the researchers trawled the cave for DNA, which they could sequence to see what kind of animals and plants were there. The fauna included bats, mice and other rodents, marmots, goats, and sheep, as well as birds, though this could have come from more recent occupancy. Plant DNA included forest species like spruce, pines, grasses, and palms. The disappearance of cold-adapted species and forest trees that gave way later to Joshua trees and grasses suggests that the sediments in the cave did go through the late Glacial Maximum, which was followed by a period of dryness.

Notably, no human or humanoid DNA was found in the cave, which would have gotten people much more excited about this find.

THE UPSHOT

How strong is the evidence for human presence in the Americas beginning 30,000 years ago? The 30,000 years is a guess by the authors, derived from guessing how long it would take humans to get to a 26,000-year-old cave residence in Mexico after crossing from Siberia. In terms of the age of the cave itself, that seems reasonable, but the evidence for human occupation is largely the “tools”, and their provenance is doubtful. And if humans inhabited the cave continuously for millennia, as the authors suppose, then why wasn’t human DNA found there? My judgment, and I’m a tyro here, is that the evidence is intriguing but not terribly strong. A lot hinges on whether the “tool-like” stone artifacts really were chipped by hominin hands.

On the other hand, the Science article says that there is a cave in the Yukon that’s yielded dates as old as the Mexican cave (about 24,000 years), but although it contains thousands of animal bones, there are “few stone tools or cut marks.” But other researchers are beginning to think that people came to America earlier than we thought, and could have spread quickly by traveling along the West coast by boat, avoiding the largely frozen interior. Here’s a tweet (h/t: Matthew) showing sites where there could have been earlier habitations:

How good are the dating methods?  From what I read, they seem fairly reasonable, and they used at least two methods that give about the same dates. The question is not how old the cave is, but whether humans lived there and made the tools and charcoal.

What happened to the people? Part of the reason we think humans have been in the New World for only 15,000 years is not just evidence from habitation, but from DNA of Native Americans (note: there are some older estimates). If that’s the case, why doesn’t the DNA give a consistent age of 30,000 years from when Native Americans branches off from East Asians? One possibility is that the early arrivers went extinct without leaving descendants, so we wouldn’t find a genetic signature of their existence. Given that some paleoanthropologists see evidence of an early arrival from other sites, like that in the Yukon, the possibility of extinction seems unlikely.

All in all, this is an exciting finding, and may well be right, but we’ll have to let the experts fight it out.

Excavating in the cave, a photo from the Science precis:

(from precis): Researchers dug nearly 3 meters deep in Chiquihuite Cave and found almost 2000 stone tools. DEVLIN A. GANDY

h/t: Matthew Cobb

____________

Ardelean, C.F., Becerra-Valdivia, L., Pedersen, M.W. et al. 2020. Evidence of human occupation in Mexico around the Last Glacial Maximum. Nature (2020). https://doi.org/10.1038/s41586-020-2509-0

Nathan Lents on the imperfection of the human body (it’s evolution, of course)

January 10, 2020 • 12:45 pm

UPDATE:  I found out that the well-known evolutionary geneticist John C. Avise published a related book in 2010, but one that concentrates on a different line of evidence for evolution. John’s book (screenshot of cover below with link to Amazon) lays out the many suboptimal features of the human genome. He thus concentrates on molecular evidence, noting the many features in that bailiwick whose imperfection gives evidence for evolution and against intelligent design.  Lents’s and Avise’s books thus make a good pair, since the former seems to deal mostly with anatomy and physiology and the latter with molecular data. I’ll be reading both of them.

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Biologist Nathan Lents, whose abbreviated c.v. is given below, has been featured on this site before, both as a critic of creationism (good), but also as a defender of the Adam-and-Eve apologetics pushed by his religious friend Josh Swamidass (bad). But chalk up another two marks on Lents’s “good” side.  First, he’s written a book (click on screenshot below) that lays out all the suboptimal features of the human body—features whose imperfection gives evidence for evolution. I’m getting the book for teaching purposes, and here’s the Amazon summary:

Dating back to Darwin himself, the “argument from poor design” holds that examples of suboptimal structure/function demonstrate that nature does not have a designer. Perhaps surprisingly, human beings have more than our share of quirks and glitches. Besides speaking to our shared ancestry, these evolutionary “seams” reveal interesting things about our past. This offers a unique accounting of our evolutionary legacy and sheds new light on how to live in better harmony with our bodies, in all their flawed glory.

Nathan Lents is Professor of Biology at John Jay College and author of two recent books: Not So Different and Human Errors. With degrees in molecular biology and human physiology, and a postdoctoral fellowship in computational genomics, Lents tackles the evolution of human biology from a broad and interdisciplinary perspective. In addition to his research and teaching, he can be found defending sound evolutionary science in the pages of Science, Skeptic Magazine, the Wall Street Journal, The Guardian, and others.

And here’s a half-hour Center for Inquiry talk, clearly based on his book, in which Lents discusses how the flaws in the human body instantiate evolution. It’s not just that there are flaws—which support the notion that natural selection doesn’t produce absolute perfection, but simply the best result available given the existing genetic variation—but, more important: those flaws are understandable as the result of our evolution from ancestors who were different from us.

Some of Lents’s examples (like our broken gene in the Vitamin C synthesis pathway), are discussed in WEIT, but others, like the bizarre configuration of our nasal sinuses, aren’t. I haven’t seen the book, but it looks like a good compendium of evidence for evolution using something that everyone’s familiar with: the glitches and bugs in the human body.

It’s a good talk, and Lents is an energetic and lucid lecturer. I recommend that you listen to this, for you’ll learn stuff that will stay with you, and also serve to help you argue with creationists.

h/t: Michael

New discovery: Earliest pictoral art in human history

December 20, 2019 • 9:45 am

A new report in Nature displays what is said to be the oldest “figurative artwork” in the world—work that is representational of real-world items rather than just abstract figures.  It shows not only hunting scenes, but “therianthropes” (human-animal hybrid figures), and also is the oldest “narrative art”, as it’s said to depict a hunting scene.  (Click on screenshot below to read the article, and you can find the pdf here).  How old is it? Uranium/thorium dating places a minimum age of the cave paintings at 43,900 years, making it older than the oldest nonrepresentational art: a disk dated at 40,800 years from Spain. 

The authors start the paper with a history of “oldest” art, which I’ll reproduce below (I have photos of the stuff that I’ve put in bold):

Previous uranium-series (U-series) dating has suggested that the oldest known figurative cave art is found in Indonesia. Up until now, the earliest minimum U-series ages for representative artworks reflect dates of 40 ka for a naturalistic painting of a wild bovid in Kalimantan and, from south Sulawesi, 35.4 ka for a painting of a pig—possibly a female babirusa or young Sulawesi warty pig (Sus celebensis). Non-figurative rock art dated to 65 ka in Spain has been attributed to Neanderthals, but this claim has been questioned on various grounds. With a minimum age of 40.8 ka, the earliest dated art that is generally attributed to modern humans in Europe is an abstract ‘disc’ sign from the rock art site of El Castillo in Spain. Although animal motifs are abundant in the Pleistocene cave art of Indonesia and Europe, in both regions humans hunting fauna are very seldom depicted; composite human–animal figures are also uncommon. In Europe, images of lone animals that are seemingly impaled by projectiles are documented in art of Magdalenian cultures (dating to about 21–14 ka); however, the motifs that are regarded by some as spears or arrows are subject to varying interpretations In terms of parietal imagery, one of very few obvious narrative compositions is the famous scene from the shaft (or ‘well’) at Lascaux (France) (Extended Data Fig. 1). This Magdalenian rock art panel apparently depicts a bird-headed man being charged by a wounded bison. The shaft scene is the subject of considerable speculation, but some scholars believe it represents a real hunt; if this is the case, so far as we can ascertain this would be the oldest narrative composition that portrays a hunting scene in European art. The earliest image that is generally accepted to represent a therianthrope is the Löwenmensch (‘lion-man’) figurine, a 31.1-cm-tall mammoth-ivory statuette of an apparently part-human, part-lion creature from Hohlenstein–Stadel (Germany) (Extended Data Fig. 1). This artefact, which belongs to the early Aurignacian tradition (dating to about 40–39 ka), is regarded by some as the earliest evidence for the capacity to link the concepts of ‘animal’ and ‘person’ into a single abstract category. The Hohlenstein–Stadel figure also has a prominent role in scientific debates about the origins of religion, as it has been argued that the ability to imagine the existence of things that do not exist—including therianthropes—forms the basis for religious thought. In Kalimantan, U-series dating has shown that people began painting small anthropomorphic figures inside caves at least 14 ka, and perhaps as early as 21–20 ka—these figures are sometimes shown pursuing deer, but dates are not available for any of these scenes. To our knowledge, no unambiguous depictions of therianthropes have previously been identified in the early cave art of Kalimantan or Sulawesi.

Here are some pictures of the images put in bold in the text.  First, the abstract disks at El Castillo, dated to at least 40,800 years and the oldest art of any kind. There are also handprints made by blowing pigment around a hand, which really conjures up our ancient relatives as people.

Disks:

Hands:

The 40,000 year old bovid figure from Borneo, previously the oldest figurative art:

From source: A painting of wild cattle, dated at about 40,000 years old, in a cave in East Kalimantan, Borneo, part of a large panel containing at least two other animals. Photograph: Pindi Setiawan

And here, from the supplementary data in the new Nature paper, are several other pieces of artwork mentioned above, including the Lascaux cave painting, which shows the bird-headed man (all captions are from the Nature paper).  The art at Lascaux is much younger: 21,000-14,000 years ago. You can also see the lion-man therianthope statue, which is about 39,000-40,000 years old, and is already quite sophisticated.

a, b, The shaft scene from Lascaux (about 21–14 ka) (a). This rock art panel is widely interpreted as depicting a bird-headed human figure (b) being charged by a bison that it has wounded with a spear; in a, the latter object is visible below the partly disembowelled bison. Another object depicted in this scene possibly represents a spearthrower with a sculpted representation of a bird at the proximal end. c, d, The lion-man figurine from Hohlenstein–Stadel. Carved in mammoth ivory, this 31.1-cm-tall image of Aurignacian age (about 40–39 ka) appears to represent a male human figure with the head of a cave lion. The image in b is a digital tracing of the relevant section in a. Sources: Alamy, used under licence (a, c); Shutterstock, used under licence (d).

The new finds are from Sulawesi in Indonesia, with the location given below. The paintings are badly weathered (I presume they’ll find a way to protect them), but have also been marred by water seeping through the paintings and then mineralizing, forming calcium carbonate concretions called “coralloid speliotherms”, or “cave popcorn”. However, the fact that the paintings were later marred by mineral deposits also gives us a way to date them, since cave popcorn can be dated using decay rates of uranium into thorium.

The limestone cave of Leang Bulu’ Sipong 4 is a rock art site in the tower karst region of Pangkep. Map data: STRM 1 Arc-Second Global by NASA/NGS/USGS and GEBCO_2014 Grid version 20150318 (http://gebco.net). Base map created by M. Kottermair and A. Jalandoni.

So at last we get to the cave art in Sulawesi, which has been enhanced in the figure below, and then given representations in b).  In c) and d) you can see enlargements showing what the authors take to be human/animal hybrids, and then a very large anoa, which is a midget buffalo found only on Sulawesi. I’ve put a picture of one species of anoa below the figure.

a, Photostitched panorama of the rock art panel (using photographs enhanced with DStretch). Ther, therianthrope. b, Tracing of rock art panel showing results of U-series dating. Scale bar, 20 cm. c, d, Detail of a group of therianthropic (part-human, part-animal) figures confronting an anoa. As evident in a, c, d, the surface of the cave wall is extensively exfoliated, erasing some of the art. However, the following elements (from left to right; see a, b) are clearly discernible: a hunter (therianthrope 1; 26 × 12 cm) apparently spearing or roping a pig (pig 1; 123 × 58 cm), in which the body of the hunter appears to be human-like in form but has a tail (Extended Data Figs. 3, 4); a lone pig (pig 2; 84 × 42 cm) (Extended Data Fig. 3); a small anoa (anoa 1; 51 × 24 cm) with an unidentified (possibly human) figure beside it (Extended Data Fig. 5); a small figure (therianthrope 2), the head of which is missing and which is positioned above an anoa (anoa 2; 74 × 29 cm) that it is possibly spearing or roping—the figure appears to be a fully composite being that apparently combines the characteristics of a human and two kinds of non-human animals (an anoa and a reptile) (Extended Data Fig. 5); a group of six very small figures (about 4–8 cm tall) (therianthropes 3–8) confronting an anoa (anoa 3) with ropes or spears—these tiny figures generally have anthropomorphic bodies, but heads and/or other body parts that are animal-like in form (for close-up images of each of the figures, see Extended Data Fig. 6). Another anoa (anoa 4) is positioned behind anoa 3, but only its head and back line are complete. The locations of four coralloid speleothems (samples BSP4.2 to BSP4.5) collected in association with three animal figures, and which yielded minimum U-series ages for the rock art panel, are indicated in the central tracing (b). The earliest minimum date for each sample is provided. The only elements that are evidently not coeval in time with the therianthropes and animals are two separate clusters of hand stencils32; these motifs were created using a lighter shade of red pigment and are differentially weathered, and one group of stencils was clearly superimposed onto pig 1 following a period of weathering of the cave wall surface, indicating a considerable time lapse between these two phases of art production (Extended Data Fig. 3). In Maros–Pangkep, the oldest dated hand stencil of the distinctive narrow-fingered style32 has a minimum U-series age of 17.8 thousand years9.

A lowland anoa (Bubalus depressicornis). There’s also a mountain anoa, and it’s not clear which species the painting above represents—or whether it’s a third species that’s now extinct. Both living species are endangered by hunting and habitat loss. These little creatures are only about a meter high at the shoulder.

The authors conclude that this is the world’s oldest known figurative art and also the oldest narrative art, which implies that humans were already engaged in storytelling 43,000 years ago. The authors consider storytelling important because “the ability to invent fictional stories may have been the last and most crucial stage in the evolutionary history of human language and the development of modern patterns of cognition.” Of course, they’re speculating here.

Finally, these are also the oldest therianthropes: almost twice as old as the Lacaux “birdman” and several millennia older than the lion-headed figure which held the previous record.  At the end, of course, there’s the requisite speculation about spirituality, as the authors say the scene “hints at the deeply rooted symbolism of the human-animal bond and predator-prey relationships in the spiritual beliefs, narrative traditions, and image-making practices of our species.” Well, again that’s more speculation. But it does suggest that about 43,000 years ago, H. sapiens was already thinking in numinous terms, for what else would a therianthrope represent?

The biology of male aggression, and why it’s not all “socialization”

December 19, 2019 • 1:15 pm

While I’ve long been a critic of evolutionary psychology, I’m not stupid or woke enough—unlike some bloggers I won’t name—to dismiss the entire field as worthless. While it’s hard to test whether some behaviors in our species have evolved by natural selection, there are degrees of confidence we can get, and predictions one can make, to judge the likelihood that these behaviors are indeed “darwinian.” While nobody argues that behaviors like preferring your own children over others aren’t products of natural selection, there are those who claim that behavioral differences between men and women are not—and in fact cannot—be based on genes installed in our species by natural selection.

The two sex differences I find most evolutionarily convincing involve human sexual behavior—in particular the observation that males tend to be relatively indiscriminate in choosing someone to mate with, while females are pickier—and the fact that males are more aggressive than females. I feel that these behavioral differences are likely, at least in part, to be the result of sexual selection in our ancestors. I won’t talk about sexual behavior today, as I’ve written about it before, but I do want to highlight an article from last April discussing the evolution of male aggression. It’s by Steve Stewart-Williams, an associate professor of psychology at the University of Nottingham Malaysia Campus, and appeared online in in Nautilus. It’s a short but good summary of why the greater aggressiveness of men than of women almost certainly reflects, at least in part, natural selection in our ancestors. Click on the screenshot to read it, and you should:

I should first emphasize that while Stewart-Williams and I share the view of the evolutionary roots of some male aggression, we both agree that males can also be socialized into being more aggressive by being expected to conform to stereotypes of “masculinity” (remember the car race in Rebel Without a Cause?); and that even if males are more aggressive than females because of natural selection, that doesn’t mean that you can’t make them less aggressive—also by socialization. Any geneticist knows that, for nearly all traits, heredity is not destiny, and the environment can make a big difference.

Nevertheless, the SJW view of differences between men and women’s behavior is that all of those differences are due entirely to socialization, with no moiety due to genetics and evolution. That is an ideological stand that, in view of the substantial morphological differences between men and women, is pretty insupportable.  And that view comes from the fear that if we do find evolution-based differences, it will lead to discrimination—usually against women. My own view is that any genetic differences we see cannot support any moral or legal inequality between the sexes, which is a philosophical position that shouldn’t depend on biology.  (If it did, equality would change as our knowledge of biology changed.)

So I deplore those who try to pretend that differences either don’t exist, or can’t have an evolutionary basis, simply because it’s inconvenient for their ideology. (They always pretend that their criticism is based on science, but they don’t fool anybody with two neurons to rub together.) That’s why the same people who will admit that men are bigger and stronger than women because of genetics and evolution will also assert that there can be no behavioral or psychological differences due to genetics and evolution. 

The caveats duly presented, Stewart-Williams gives several lines of evidence for an evolutionary origin of this behavioral difference. I’ll summarize them briefly; the indented sections are Steve’s writing.

1.) The behavior is consistent across different cultures, when one would expect different degrees and kinds of socialization.

An initial line of evidence is that it’s not only in the West that we find sex differences in aggression. Wherever in the world we look, men are more violent and aggressive than women, especially with other men. The clearest and most persuasive evidence for this comes from homicide statistics: In every country, without fail, men commit the vast majority of homicides (and are more likely to be the victims of homicide as well). If the sex difference in aggression is just an arbitrary product of culture, why does it rear its ugly head in every human group?

Now there are those, says Stewart-Williams, who argue that the difference in aggression is just a non-evolved byproduct of differences in size and strength. If you’re bigger and stronger (presumably for evolutionary reasons), then you can benefit by being more aggressive, and you get pigeonholed into social roles that involve more strength and aggression. But that raises the question of why men are bigger and stronger than women! While you’ll see social-justice warriors trying desperately to explain size and stength differences without invoking sexual selection, a reasonable explanation, based on observations below, including the behavioral differences in sexual behavior as well as parallels from animals like seals and gorillas, is that part of the size/strength differentiation involves men competing for women: to the stronger goes the reproduction.

The avoidance of sexual selection as an explanation is because that implies that there could be behavioral differences between men and women as well (sexual selection involves behavior), and to the Authoritarian Left that idea is to be avoided at all costs.

Here’s how Stewart-Williams rebuts the “byproduct” explanation for differences in aggression:

It’s a clever argument, and one worth taking seriously. On balance, though, I don’t think it flies. To begin with, the Eagly–Wood theory raises some awkward questions. Why wouldn’t natural selection create psychological sex differences as well as physical ones? The mere existence of the physical differences tells us that human males have been subject to stronger selection for aggression and violence than females. Why would this selection pressure shape our muscles, our skeletons, and our overall body size, but draw the line at our brains? And why would natural selection give men the physical equipment needed for violence but not the psychological machinery to operate it? This would make about as much sense as giving us teeth and a digestive system, but not a desire to eat.

That is a strong argument, and one that I haven’t seen rebutted by the haters of evolutionary psychology. Why are our brains the one organ that can’t be differentiated between men and women by selection?

2.) We don’t find, as expected under the socialization theory, larger amounts male aggression in societies that have stricter gender roles and less gender equality.

On top of that, if sex differences in aggression were all down to gender roles, the differences would be larger in cultures with stricter gender roles and greater gender inequality. That’s not what we find, though. On the contrary, it seems to be the other way round. A recent large-scale, multinational study revealed, for instance, that sex differences in adolescent physical aggression are smaller, rather than larger, in less gender-equal nations. Culture clearly matters when it comes to sex differences in aggression—but the effect of culture is apparently very different than the social role theory would lead us to expect.

3.) Males are more aggressive than females from the very beginning of childhood, presumably before they’ve had a chance to be socialized.

. . . the sex difference in aggression appears very early in life—usually before children take their first bite of their first birthday cake. From the moment they can move around under their own their steam, boys engage in more rough-and-tumble play than girls. The same sex difference is found in other juvenile primates, and appears to be related to testosterone exposure in the womb. In humans, the sex difference shows up long before kids understand that they’re boys or girls, so it can’t just be that they’re conforming to social expectations about how boys and girls ought to act. In any case, children are terrible at conforming to social expectations, as any parent who’s tried to persuade their progeny to sit nicely and quietly in a restaurant will readily confirm. And not only does the sex difference in aggression emerge early, it remains static until puberty. Absolute levels of aggression trend downward for both sexes; however, the gap between the sexes barely budges. If socialization creates the sex difference, why doesn’t continued socialization before puberty pry the sexes apart?

And here I should add that testosterone has a positive effect on aggression, whether injected or naturally circulating in people with abnormal levels of the hormone for their sex. That, too, points to an evolutionary explanation.

4.) The pattern of male aggression conforms to what we expect if it evolved to promote competition for females.  Stewart-Williams reports that early differences in aggression remain static until puberty, when males suddenly become much more aggressive and much more willing to take risks.  This would be expected because male aggression would be most adaptive when the reproductive benefits are greatest—during early reproductive years (in our relatives, of course, who probably began reproducing much earlier than modern humans). As Stewart-Williams argues:

How would the Nurture Only approach explain the violence gap that opens up between the sexes at puberty? Is there a sudden surge in gender socialization—a surge which, for some unknown reason, happens at exactly the same stage of life in every culture and in many sexually dimorphic species? Is it just a coincidence that this alleged surge in socialization comes at the same time as the massive surge in circulating testosterone that accompanies puberty in males?

He adds that after early adulthood, male aggression goes down steadily for the rest of a man’s life, something that the socialization hypothesis doesn’t explain but the evolutionary hypothesis does: why be aggressive when you get little reproductive payoff but risk being killed or injured by other, younger males?

5.) In many species of animals, including our closest relatives, males are more aggressive than females. If you have a “socialization” theory, you’d have to claim that what everyone accepts in other species as evolved differences in behavior just happen to be the nonevolved products of socialization in humans. What a remarkable coincidence!

A final line of evidence that sex differences in aggression have biological underpinnings is that these differences are not unique to human beings. Indeed, in some cases, the parallels across species are striking. Consider humans and chimpanzees. Among humans, males commit around 95 percent of homicides, and are around 79 percent of homicide victims. Among chimps, on the other hand, males commit around 92 percent of “chimpicides,” and are around 73 percent of chimpicide victims. In short, the sex difference in lethal aggression in the two species is remarkably similar in size.

That’s all I’ll say for now, except to add one more argument that is mine: the aggression difference also goes along with the sexual “choosiness” difference that has been repeatedly observed in psychological studies. Both bespeak a form of sexual selection in which males compete for females and females are choosy about who they select as mates.

I’ll also warn readers that many people who argue against any evolved behavioral difference between men and women are people who likely have an ideological agenda. And they often pretend that they don’t.

At the end, Steve tells us that it’s important to understand the roots of male aggression because it helps us reduce male violence that is harmful in today’s world (my emphasis):

None of this implies, by the way, that we’re necessarily stuck with male aggression, or stuck with aggression in general. As the psychologist Steven Pinker demonstrated in The Better Angels of Our Nature, levels of violence and warfare have fallen steadily over the decades, centuries, and millennia, despite the fact that aggression is part of human nature. In various ways, from policing and government to trade and moral norms, we’ve managed to pull ourselves, to a significant extent, out of the vortex of violence and bloodshed that characterized our species for the bulk of its tenure on Earth.

If we want to continue on this trajectory, however, or ideally to hasten our progress, our best bet is presumably not to delude ourselves about the true causes of our behavior. As policy wonks like to say: Wrong diagnosis; wrong cure. Let’s get the diagnosis right so that we can maximize our chances of curing the scourge of human violence.

I agree with the malleability bit in the first paragraph, but am not so much on board with the idea that we need to understand what causes our behavior because it will help us alter our behavior. After all, whether male aggression be due to socialization, evolution, or a combination of both factors, the treatment is the same: socialize men to be less aggressive!  The reason I want to know what causes our behaviors is pure curiosity.

Bogus accommodationism: The return of Adam and Eve as real people, as proposed by a wonky quasi-scientific theory

October 11, 2019 • 9:00 am

If you’re a liberal Christian scientist (no, not the Mary Baker Eddy kind, but the profession), and would like to persuade more fundamentalist Christians that evolution really happened, what do you do? Well, Joshua Swamidass at Washington University, with the help of his secular friend scientist Nathan Lents (a professor of biology at John Jay College of Criminal Justice), have decided to promote the idea that Adam and Eve really existed as people created by God a few thousand years ago, with Eve made from Adam’s rib.

It turns out that Swamidass has a new theory, which is his, that we can designate a God-created couple as the genealogical ancestors of all living humans—a couple that lived around 5,000 years ago. Then that couple supposedly interbred with other humans who themselves were the result of pure evolution and who lived side-by-side with Adam and Eve (henceforth A&E). This interbreeding wound up with the Original Sin of Adam and Eve being passed on to everyone living, even though the genes of Adam and Eve don’t linger on in modern humans, much less in all of us. That is, A&E were our genealogical ancestors but not our genetic ancestors. They are in the lineage of all of us and bequeathed us Original Sin rather than any genes.

The big advantage of Swamidass’s theory (to Swamidass and the Christians he’s trying to convert) is that his theory is untestable: a speculation that cannot be confirmed or denied by evidence, since there would be no genetic trace of these ancestors in living humans (see explanation below). Swamidass thinks that’s a big advantage because it allows literalist Christians to accept both evolution and Adam and Eve, and that his theory and new book will facilitate that shift. I think he’s dead wrong, and for the very same reason that the BioLogos organization, which spent a lot of time trying to figure out how to reconcile A&E with evolution, completely failed in its mission to turn evangelical Christians toward evolution. Adam and Eve, like Jesus’s resurrection, is a story that cannot be turned into a metaphor. If it was just a metaphor, why are all of us sinful and need redemption by accepting Jesus?

Swamidass’s view is presented in an upcoming book (out December 10) issued by InterVarsity Press, a publisher of evangelical Christian books (click on cover below for a description):

And Lents has given the book a boost with an opinion piece in, of all places, USA Today (click on screenshot to read it, and thanks to the many readers who sent me the link):

Swamidass’s description of his “theory” can be seen by clicking on this website post from the site Peaceful Science:

or this paper (free pdf, click on screenshot) in the journal Perspectives in Science and Christian Faith:

How does the theory work? In brief, it’s based on the fact that because each of us has an increasing number of genealogical ancestors as we go back into the past, it becomes inevitable that the lineages of different people will intersect at common ancestors. Each of us has two parents, four grandparents, eight great-grandparents, and so on. Since there are about six billion of us on the planet, you can see that only three generations ago there would be 48 billion putative ancestors—more than the number of people on Earth. And as you go farther back, that number grows rapidly.

Because there weren’t that many people alive to be independent ancestors of us all, we must have had common ancestors just a few generations ago. And as you go further back, you can estimate that there were only a few people who were common ancestors of all living humans. Finally, you can calculate how far back you’d have to go until one person (a couple, actually, since they’d have to leave offspring) is a common genealogical ancestor of all living humans. That is the Most Recent Genealogical Common Ancestor, which I’ll call the MRGCA.

As Douglas Rohde et al. calculated in this 2004 paper in Nature, the most recent common ancestor of everyone could have lived as recently as 5,000 years ago, although there’s substantial error around that date and the calculation involves a number of assumptions.  But even if it’s off by, say, a factor of four, that’s probably okay with many Christians, since most evangelicals wouldn’t hold strictly to the 6,000 year-old A&E calculated by Bishop James Ussher (ironically, “Primate of All Ireland”) in 1650.
Now the genealogical common ancestor is not a genetic common ancestor: it’s likely that many people on Earth don’t have any genes from this putative First Couple. That’s because while genes get diluted out of descendants with time (and because the A&E mated with existing humans that, says Swamidass, evolved from australopithecines in the way scientists accept), genealogies don’t get diluted: they are just fixed lines of descent, which in this case all converge at a relatively recent “A&E”. 

We also know that Swamidass’s A&E aren’t our sole genetic ancestors from a lot of data, including the calculation that the minimum population size of the lineage leading to modern Homo sapiens would have been about 12,000: this comes from back-calculation of how many people would have been needed to contain the genetic variability we see in modern humans. Also, we have dates for “mitochondrial Eve” and “Y-chromosome Adam” of about 150,000 years ago and 200,000-300,000 years ago respectively. Not only are these dates way older than most Christians would place Creation and the Garden of Eden, but these A&Es didn’t even live at the same time. (These individuals are the most recent genetic common ancestors of the mitochondrial DNA and of the Y chromosome, respectively, since these bits of DNA are largely inherited as units.)

Swamidass accepts the existing genetic data, because he’s concerned only with genealogical lineages, not who gave us our genes. Using genes would negate the idea of A&E.

Presumably Original Sin, which is also important for Swamidass since it must be preserved as part of literal Christianity, is inherited somehow along lineages but not via the genome. (How Original Sin spreads to all the descendants of the MRGCA without dilution is a mystery left for Swamidass and the theologians.)

If you think I’m exaggerating Swamidass’s thesis, here’s his claim from the website post linked above:

Entirely consistent with the genetic evidence, it is possible Adam was created out of dust, and Eve out of his rib, less than 10,000 years ago in a divinely created garden where God might dwell with them, the first beings with opportunity to be in a relationship with Him. Perhaps their fall brought accountability for sin to all their descendants. Leaving the Garden, their offspring blended with their neighbor in the surrounding towns. In this way, they became genealogical ancestors of all those in recorded history. Adam and Eve, here, are the single-couple progenitors of all mankind. Even if this scenario is false or unnecessary, nothing in evolutionary science unsettles this story. So, evolution presses in a very limited way on our understanding of Adam and Eve, only suggesting (alongside Scripture) that their lineage was not pure.

Swamidass adds this:

Though I personally do not endorse any specific account, not even this one, the point is that the scientific evidence does not unsettle this literal, traditional, and concordist account of Genesis. From a scientific point of view, most of the details in this account are not important; the dates can shift, and so can the theology. As long as there is mixing with those “outside the garden,” this account is consistent with all the findings of evolutionary science. There are no hermeneutical or theological claims embedded in this claim. Rather, scientifically speaking, this account fits without contradiction into the evolutionary account of our origins.

And although the dates of genetic common ancestors (which of course differ for nearly all of our genes, since they recombined in the past with other genes and “coalesced” at different times) can be tested, and it can be shown that there was no pair of contemporaneous humans that gave all of us our genetic legacy, the genealogical A&E has the convenient advantage of being untestable. Or so Swamidass says:

Despite what we have heard, science is silent on Adam and Eve, ancestors of us all. Science is also silent about whether they were de novo created, much as it is silent on the Resurrection.

. . . . Science is silent, therefore, on Adam and Eve, ancestors of us all. They might even be de novo created from the dust, and from a rib, and lived less than 10,000 years ago. Science tells us nothing about them. Instead, we must turn to theology and hermeneutics. Here, the conversation is set for some very important and engaging dialogue between science and theology.

Yes, dialogue based on questions like these, some of them raised in the piece by Faizal Ali noted below. Here are three questions:

1.) If the Bible doesn’t mention other humans living at the same time as Adam and Eve, who were they? Swamidass thinks that they were the population of humans who evolved from our common ancestor with chimps, but Christians won’t buy that. They’d have to resort to the kind of exegesis that gives answers to questions like “Who did Cain and Abel marry?”

2.) How do we know this pair was created and resided in the Middle East (a requirement for Christians)? We don’t: that’s another thing that’s untestable.

3.) What about earlier Adam and Eves? It’s certain that the MRGCA was preceded by earlier genealogical common ancestors, so there are many candidates for A&E, not just the most recent ones. Swamidass picks out the most recent one because it allows Christians to comport a Biblical chronology with the scientific data. But, as Brian Charlesworth pointed out to me in an email discussion I had with him and geneticist Joe Felsenstein, we could have had something like this, with Arthur the Australopithecus and his mate being older equivalents of Adam and Eve (Brian made this graph). The lines represent genealogies, with Joe and I being more closely related because we’re both Jews:

Most important, and the thing that really bothers me about this hamhanded attempt to resuscitate an Adam and Eve that comports with science, is the point made by Faizal Ali in his post below (click on screenshot):

From Ali:

Swamidass states several times in his summary that “science is silent” on the idea of a de novo creation of Adam and Eve. This is not accurate, in my view. Science is quite clear that human beings do not spring into being from a pile of dust. That is just not how it happens. Science is as clear on this question as it is on the fact that rocks do not stay suspended in mid air, impervious to gravity, when you let them go while standing on the surface of the earth. What I believe Swamidass actually means is that, if we presume the existence of an omnipotent God who is capable of performing miracles, then the fact that it is not scientifically possible for a human being to instantly spring into being from dust does not mean it will not ever happen. Which is true as far as it goes. However, why stop there? Young Earth Creationists, who insist that the universe is only 6000 years old, will often wave away the overwhelming scientific evidence that the universe is actually billions of years old by saying that God could have created the universe 6000 years ago with the appearance of being billions of years old, just as he created Adam to look like a mature adult at the moment of his creation.

I see no reason that a god who could, and would, create a pair of special organisms who are physically identical to human beings could not, and would not, create a universe that, from its inception, appeared to be billions of years old. Why not? The difference between the two is simply that Swamidass’s theology requires a literal Adam and Eve, but not a young earth. For the person whose theology requires both, Geneaological Adam and Eve offers no solution. And my concern is that Swamidass’s scenario serves to validate and legitimize this sort of sloppy thinking.

. . . Swamidass. . . seeks to circumscribe science and install a firewall between it and religion, such that each discipline works in relative isolation from each other. As such, I do not see his scenario holding much attraction for creationists of various stripes whose true ambition is to bring science to heel and make it subservient to scriptural revelation. I suspect this is what the Intelligent Design Creationist Ann Gauger means when she says of Swamidass’s model that she views “the cost as too high.”

What we have, then, is a scientist proposing a scenario he doesn’t really accept, and one that really does violate science by negating what we know about how humans appear—all in the vain hope that it will convert evangelical Christians to evolution and science. “Hey,” Swamidass thinks they’ll say, “There could have been an Adam and Eve after all. Now I’m totally down with Darwin!”

From what I’ve seen of creationists, this won’t happen. Maybe one or two might buy this hokey scenario, but the rest, knowing that the scenario requires that all of us evolved genetically from a common ancestor with apes, and that this began 6 million years ago in Africa, will reject it, as Gauger did.

Swamidass has an honorable aim, but the cost is too high for me, too, since it requires perverting science and accepting miracles for which there can be no evidence. If you take the stand that “anything can be true, and if there’s no evidence for it one can believe in it”, then you’re buying into leprechauns, fairies, and a whole host of other unevidenced superstitions. Swamidass and Lents are supporting those superstitions, thereby buttressing the acceptability of faith as strong belief that doesn’t require credible evidence. That’s the kind of attitude that pervades evangelical Christianity and many other religions, and it’s an attitude that needs to be expunged from today’s world.

I look forward to Swamidass’s analysis of how Original Sin spread from the recent A&E to all existing humans. It can’t behave as a gene, and it must remain undiluted as it passes among generations after matings with non-created humans. Swamidass now bears the responsibility of telling the Christians he’s addressing exactly how that works.

As for me, I continue to adhere to Hitchens’s Razor:

What can be asserted without evidence can also be dismissed without evidence.

Vestigial limb muscles in human embryos show common ancestry—for the gazillionth time

October 6, 2019 • 9:00 am

There are three kinds of vestiges that constitute evidence for evolution, or rather its sub-claim that modern species share common ancestors. I discuss all three in Why Evolution is True:

1.) Vestigial traits that persist in modern species but either have no adaptive function in a species or a function different from the one served in that species’ ancestors. The vestigial ear muscles of humans are one, the flippers of penguins (functional, but not for flying in the air) is another, and the coccyx in humans (sometimes with attached “tail muscles” that can’t move it) is a third.

2.) Vestigial genes that are functional in our relatives (and presumably in our ancestors) that have been inactivated in some modern species. There is no explanation for these “dead genes” save that they were useful in ancestors but aren’t useful any longer. Examples are “dead” genes that code for egg yolk proteins in humans (but don’t produce them); a dead gene for vitamin C synthesis in humans (we don’t make the vitamin because that gene is inactivated, but rather get it from our diet; and the many dead “olfactory receptor” genes in cetaceans (whales, dolphins, etc.)—genes that were active in their terrestrial ancestors but became inactivated because “smelling” underwater uses different genes and traits.

3.) Features in development that are transitory, and whose appearance makes sense only under the supposition that those features were present in common ancestors and persist in some descendants but not others. The lanugo (a transitory coat of hair in human embryos) is one.

Today’s paper, which just appeared in the journal Development, shows several other “transitory” evolution-attesting features. Diogo et al. show that human embryos develop muscles that disappear as development proceeds, but those muscles don’t disappear in some of our relatives, including closely related ones like other primates as well as distant relatives like reptiles.

Moreover, these muscles, which disappear in most human embryos, sometimes don’t disappear, persisting in adults as rare and nonfunctional variants. Or they appear in malformed individuals, with both phenomena often seen in “vestigial traits”. For example, some people are born without wisdom teeth, considered a vestigial holdover from our ancestors; and the functionality of human vestigial ear muscles that move the ears in our relatives, like cats and dogs, is variable: some people like me are able to move those muscles and wiggle their ears, while others can’t.

Click on the screenshot below to access the paper, and the pdf is here (reference at the bottom of this post).

The authors visualized the muscles in the embryonic arm and leg by doing immunostaining—using antibodies that would affix to proteins in the muscles and also carried ancillary molecules that would make those muscles more easily visualized under the microscope in a three-dimensional way. The authors used 70 antibodies, but the main ones bound to muscle-specific proteins like myosin and myogenin.

They stained the mounted limb sections of 13 embryos (presumably from abortions) ranging from nine to thirteen weeks after gestation (quantified as “gestational weeks”, or GWs), and with the standard measurement “crown-rump length” (CR) ranging from 2.5 cm to 8.0 cm (about 1 to 3 inches). These were thus very small embryos, but the sophistication of the technique, and the efficacy of the stain, combined with our knowledge of embryonic development and tetrapod muscle anatomy, enabled the authors to produce pictures like these: the muscles in the hands of a 10 and 11-GW fetus:

 

What they found is that human embryos show a number of muscles present in the adults of some other tetrapods (including our closest relatives, the chimps), but that disappear during human development, with a few of these “atavistic muscles” fusing with other muscles in human fetuses although remaining distinct in our tetrapod relatives.

Here’s how the authors describe the main results, listing some of the atavistic muscles in the embryos (I’ve put them in bold):

As summarized in Tables 2-5 and also noted above, various atavistic muscles that were present in the normal phenotype of our ancestors are present as the normal phenotype during early human ontogenetic stages and then disappear or become reduced and completely fused with other muscles, thus not being present/distinguishable in human adults. These include the upper limb muscles epitrochleoanconeus (Fig. 3), dorsoepitrochlearis, contrahentes 3-5 (Fig. 4) and dorsometacarpales 1-4 (Figs 3-5), and the lower limb muscles contrahentes 3-5, dorsometatarsales 1-4 (Fig. 6) and opponens digiti minimi (Fig. 6). These muscles are present in some other tetrapods, as shown in Tables 6 and 7, which summarize the comparisons with other limbed vertebrates. Of all these muscles, only the dorsometacarpales often remain in adults, fused with other muscles: all the others are normally completely absent in human adults. Fascinatingly, all these atavistic muscles are found both as rare variations of the normal adult population and as anomalies in individuals with congenital malformations such as those associated with trisomies 13, 18 and 21, reinforcing the idea that such variations and anomalies can be related to delayed or arrested development.

Here are two of the fetal atavistic muscles. First, the dorsometacarpales in the hand, which are present in modern adult amphibians and reptiles but absent in adult mammals. The transitory presence of these muscles in human embryos is an evolutionary remnant of the time we diverged from our common ancestor with the reptiles: about 300 million years ago. Clearly, the genetic information for making this muscle is still in the human genome, but since the muscle is not needed in adult humans (when it appears, as I note below, it seems to have no function), its development was suppressed:

 

Here’s a cool one, the jawbreaking “epitrochleoanconeus” muscle, which is present in chimpanzees but not in adult humans. It appears transitorily in our fetuses. Here’s a 2.5 cm (9 GW) embryo’s hand and forearm; the muscle is labeled “epi” in the diagram and I’ve circled it:

This muscle must have become nonfunctional, and reduced in development, over the last six million years or so, when the common ancestor of humans and chimps gave rise to our separate lineages.

An interesting sidelight of this study is that some of these vestigial muscles occur as rare variants in adult humans, either via developmental “accidents” or as part of congenital malformations. Presumably these screwups in development block the genetic changes that normally lead to the suppression and disappearance of muscles in embryos. Variable expression of vestigial traits is common in organisms where the traits haven’t evolved into something else that’s useful. (For more on human vestigial traits, see the Wikipedia article on “human vestigiality”). The authors note that when the muscles do appear in adults, they are “functionally neutral, not providing any type of major functional advantage or disadvantage.”

The presence of these vestigial muscles is pretty irrefutable evidence of evolution and common ancestry, for there’s no reason why either God or an Intelligent Designer (a pseudonym for “God” to ID advocates) would put a transitory muscle in a human fetus that’s of no use whatsoever, but just happens to resemble the fetal muscles that goes on to develop into adult muscles in our relatives.  I wonder how creationists, including IDers, will explain this as the work of a designer. Will they say the muscles are really functional in a fetus? If so, why do they disappear? And doesn’t the fact that they go on to develop into functional muscles in our relatives like chimps and reptiles say something about common ancestry?

Two more points:

1.) The order of appearance of these muscles in development doesn’t completely comport with their order of evolution. This shows that the “recapitulation theory”—that the order of development mimics the order of evolution—isn’t completely obeyed. But we’ve known that for a long time. The time of appearance of a trait in development can be changed by other factors, like its usefulness in “priming” the development of other features. But this doesn’t overturn the very strong conclusion that the presence of transitory muscles in the human fetus that remain in adults of our relatives is evidence for evolution.

2.) Finally, muscles in the arms and legs that appear “homologous” (i.e., have the same evolutionary origin) may have had independent evolutionary origins, and may involve different genes, so they’re not really “homologous” in the way evolutionists use that term. As the authors note,

These differences support the emerging idea that the topological similarities between the hand and foot of tetrapods, such as humans, are mainly secondary (see recent reviews by Diogo et al., 2013, 2018; Diogo and Molnar, 2014; Sears et al., 2015; Miyashita and Diogo, 2016). This idea is further supported by the fact that the order of developmental appearance of the hand muscles is markedly different from that of the corresponding foot muscles (Tables 6, 7). As an illustrative example, whereas the lumbricales are the first muscles to differentiate in the hand, together with the contrahentes (Table 6), in the foot the lumbricales differentiate only after most other foot muscles are already differentiated (Table 7). Thus, these developmental data and evidence from comparative anatomy and from the evolutionary history of human limb muscles (see Tables 6, 7) indicate that several of the muscles that seem to be topologically similar in the human upper and lower limbs actually appeared at different evolutionary times; appear in a markedly different ontogenetic order; derive from different primordia; and/or are formed by the fusion of different developmental units in each limb.

Now the authors didn’t do this study to demonstrate evolution; like most rational people, they accepted it long ago. Rather, their stated aim was to “build an atlas of human development comprising 3D images. . . that can be used by developmental biologists and comparative anatomists, as well as by professors, students, physicians/pathologists and the broader public.” But one of the bonuses, especially for the broader public, is the very clear demonstration of the common-ancestry tenet of modern evolutionary theory.

h/t: Liz

______________

Diogo, R., N. Siomava, and Y. Gitton. 2019. Development of human limb muscles based on whole-mount immunostaining and the links between ontogeny and evolution. Development 146: doi: 10.1242/dev.180349. Published 1 October 2019

A new and important hominin skull from Ethiopia

September 1, 2019 • 9:45 am

A new analysis of a remarkable hominin find in Ethiopia suggests that the species it represents, Australopithecus anamensis, may be one of the very earliest species in our lineage, and possibly the first hominin we know of that is undoubtedly part of our own genealogy. (“Hominins”, formerly called “hominids”, represent all fossils on our side of the family tree since we branched off from our common ancestor with the chimpanzees). The find has also has led to a revision of the idea that A. anamensis was the ancestor of the later A. afarensis, thought by many to be the ancestor of the genus Homo, and thus of modern Homo sapiens. (We love to know who our ancestors are, as witnessed by the popularity of companies like 23 & Me.)

A. anamensis lived from about 4.2 to 3.9 million years ago (mya) and A. afarensis from 3.9 to 3.0 mya. A. afarensis includes the famous skeleton of Lucy(about 3.2 mya), which is remarkably complete from the neck down but has only fragments of the skull.  As the following diagram suggests (and this is typical), A. anamensis is the earliest known hominin to be part of our own lineage and is portrayed as the ancestor of A. afarensis:

That ancestry is presumed (as shown above) to have been a lineal transformation of A. anamensis into A. afarensis: that is, the former species was thought to have evolved over time, and as a unit, into A. afarensis.

This conclusion is what is cast into doubt by the recent find, documented in a new paper in Nature that you can access by clicking on the screenshot below (or see the pdf here). The new finds show that A. anamensis was in fact a contemporary of A. afarensis, so that the two species lived at the same time, at least for a while.

This doesn’t rule out, however, the possibility that A. afarensis evolved from one or more populations of A. anamensis while the latter species continued on, largely unchanged from other populations. (Some, however, would say that such a branching event would automatically change the name of A. anamensis; see below.) Thus both species could still have coexisted while A. afarensis could still be a descendant of A. anemensis.

The paper:

As you see, the new skull is 3.8 million years old, putting it at about the end of A. anamensis‘s tenure and about the time that A. afarensis appeared.

The new skull is remarkably complete: by far the most intact A. anamensis skull we have, and also has a number of features that tell us that it was a hominin and was not a member of A. afarensis. Since the earliest A. afarensis appears to have lived a bit earlier than this specimen (3.9 mya), it appears that A. afarensis cannot be a lineal descendant of A. anamensis. (But, as I said above, it could be a descendant of some A. anamensis populations.)

Here’s the skull, which has a tiny cranial capacity (365-370 cc compared to about 1200-1300 cc in modern humans), a sagittal crest, and brow ridges.

a, Anterior view. b, Posterior view. c, Superior view. d, Left lateral view. e, Right lateral view. f, Inferior view. The specimen is oriented in Frankfort horizontal plane. Scale bar, 1 cm.

 

You can see how small the skull is when compared to the head size of the paper’s first author:

Yohannes Haile-Selassie with the skull. Photograph: AFP/Getty Images

It appears to have been an adult male.

Why is it a hominin? Well, here’s the jargon that they use to show it’s a hominin and more primitive (that is, closer in appearance to the common ancestor) than is A. afarensis:

The specimen is readily identifiable as a hominin by the following morphological features: the canine is reduced in size compared to non-human apes and shows a strong lingual basal tubercle; the mastoids are inflated; the nuchal plane is more horizontal than in non-human apes; and the inion, which is coincident with the opisthocranion, lies near the level of the Frankfort horizontal plane. At the same time, the small cranial capacity, highly prognathic face, extensive pneumatization and other features discussed below indicate that MRD represents a hominin that is more primitive than A. afarensis.

Got that? Neither did I, but the paleoanthropologists do.  At any rate, the dates put it earlier than most specimens of A. afarensis, and it has a longer upper canine, a smaller earhole, and a narrower palate. Here’s a comparison of the new specimen (MRD-VP-s/1, which we’ll call MRD) with Sahelanthropus tchadensis (a hominin that may be close to the common ancestor of the human and chimp lineages, and which lived about 7 mya), along with Australopithecus ramidus (a 4.4 mya hominin of unknown placement on the tree), and A. afarensis and the later A. africanus.

(All captions below are from the Nature paper): Red lines and arrows show the inclination of the frontal and the presence of a post-toral sulcus, respectively. Blue lines show the orientation of the mid and lower face, with an broken line indicating a segmented facial profile27. The green arrow marks the anterior projection of the zygomatic tubercle (relative to the anterior zygomatic root). Scale bar, 2 cm.

Here’s the back of the skull compared to a modern chimp and the two later australopithecines. Note the smaller braincase and more pronounced sagittal crest of MRD:

The transverse contour of the cranial base is convex in African apes, whereas A. afarensis shows an angular transition between the nuchal region and the greatly expanded mastoids (red dashed lines). In this regard, A. afarensis anticipates the morphology of robust australopiths, but A. africanus is less derived. MRD shows the primitive convex contour of the base, even though the mastoids are expanded. MRD is also primitive with regard to the great length of the nuchal plane (black arrows). However, it is similar to A. afarensis in the configuration of the compound temporal–nuchal crest (white dashed lines), the bare area (blue hatched triangle), and the overall ‘bell-shaped’ posterior outline (that is, the parietal walls are slightly convergent superiorly and the greatest width occurs basally across the enlarged mastoids).

A phylogenetic analysis of where the MRD skull fits on the hominin phylogeny. As you see, it appears before A. afarensis and sits on part of the phylogeny that gave rise to modern humans.

h, i, Cladograms from the K-combined and S&G-combined analyses (as in a and b), with apomorphies added to the cladograms to illustrate the implied pattern of evolutionary change. The character states reconstructed at nodes A and B provide the reference for identifying A. anamensis and A. afarensis apomorphies, which are shown here as rectangles containing their abbreviated character labels. Characters in red, orange, gold and green describe similar morphology and appear in both previously published studies27,33. See Supplementary Note 9 and Supplementary Table 1.

This species was sexually dimorphic, with males about five feet tall and weighing about 100 pounds (1.5 meters and 45 kilos), and females about 3.5 feet tall and weighing about 62 pounds (1.1 meter and 28 kilos). The skull size and features (tooth wear, etc.) suggest that it was an adult male. Here’s a reconstruction of the face from The Guardian:

The big findings: First, we now know what the cranium of a possible ancestor looked like, and crania are not easily preserved or found in the fossil record of hominins. This helps complete the picture of what A. amanensis looked like.  Further, another major and unambiguous conclusion here—assuming the dating is correct—is that A. anamensis coexisted with A. afarensis for at least 100,000 years.  A. afarensis is thought to be one of our ancestors, giving rise to the genus Homo as well as the extinct “robust” australopithecines. But this leaves one question:

Was A. anamensis an ancestor of A. afarensis? Just because the two species coexisted does not mean that the one who lived first wasn’t the ancestor of the one that appeared later. Consider that there were various populations of the earlier A. anamensis. Suppose one or more of these evolved into A. afarensis, but some other populations retained the appearance and traits of A. anamensis. Then we’d still have an ancestor/descendant relationship, though cladistic taxonomists would say that at the moment A. afarensis branched off, we’d have to change the name of A. amanensis. (This is part of the practice of cladistic classification, though it makes little sense to laypeople.)

Whether A. afarensis came into being this way or not, what’s clear is that two species of australopithecine lived at the same time, and one of them is thought by paleoanthrophologists, as the first diagram above shows, to have been the ancestor of several species of hominins, including us.

h/t: Pyers

“Modern” Homo sapiens may have been in Eurasia as long as 210,000 years ago

July 11, 2019 • 9:00 am

The conventional wisdom about the migration of Homo out of Africa, where the genus originated, involves the spread of Homo erectus about 2 million years ago across Eurasia, with that species appearing to have gone extinct without issue.

After that, the Neanderthals, which split from the lineage producing “modern” (i.e., living) H. sapiens about 800,000 years ago, moved to Europe some time between then and 600,000 years ago. (For convenience, I’ll call Neanderthals “Neanderthals” and “modern H. sapiens” as sapiens, though I think they’re both subspecies of H. sapiens.)

Then, it was thought, sapiens moved into Europe and then Asia beginning about 60,000 years ago, with Neanderthals becoming extinct around 40,000 years ago, though having left a genetic legacy within sapiens. (That ability to produce fertile hybrids between H. sapiens sapiens and H. sapiens neanderthalensis is why I consider both lineages to be subspecies of the same biological species).

There was, however, tantalizing evidence—as summarized in a Nature News & Views article (free with UnPaywall) about the paper discussed today—that two skulls found in Israel, dated between 500,000 and 200,000 years ago, might also been close to the “modern H. sapiens” lineage, but the evidence is fragmentary and these could actually be Neanderthals.

The figure below, from the News & Views piece, summarizes fossil finds of Homo from the Eastern hemisphere (see key at bottom of figure for species designation, and note the Neanderthals and Denisovans):

Figure 1 | Some key early fossils of Homo sapiens and related species in Africa and Eurasia. Harvati et al.5 present their analyses of two fossil skulls from Apidima Cave in Greece. They report that the fossil Apidima 1 is an H. sapiens specimen that is at least 210,000 years old, from a time when Neanderthals occupied many European sites. It is the earliest known example of H. sapiens in Europe, and is at least 160,000 years older than the next oldest H. sapiens fossils found in Europe (not shown). Harvati and colleagues confirm that, as previously reported, Apidima 2 is a Neanderthal specimen, and they estimate that it is at least 170,000 years old. The authors’ findings, along with other discoveries of which a selection is shown here, shed light on the timing and locations of early successful and failed dispersals out of Africa of hominins (modern humans and other human relatives, such as Neanderthals and Denisovans). kyr, thousand years old.

The Israeli fossil provided weak evidence that sapiens may have left Europe well before the conventional date of about 60,000 years, though these forays into Eurasia, at least judging from genetic evidence, didn’t give rise to humans living today.

Now a new article in Nature by Katerina Harvati et al. (click on screenshot below for free UnPaywall access, with pdf here and reference at bottom), suggests much more strongly that sapiens did indeed leave Africa for Eurasia much earlier than we thought: in fact, way earlier—about 210,000 years ago. That more than triples the time length of time since the first sapiens left Africa. Note, though, that the new find, even if it is sapiens (and there are doubts), is not ancestral to living modern humans; the population seems to have vanished without issue.

The paper is based on two skulls originally found in 1978 in a cave in Apidima in southern Greece, but were only now dated and thoroughly analyzed morphologically.

There were two skulls in the same place and piece of sedimentary rock, one dated at about 170,000 years ago (“Apidma 2”) and the other a bit older at 210,000 years (“Apidima 1”). Apidima 2 is represented by a pretty complete cranium, minus the jaw, while Apidima 1 is only the rear of the skull. The fossils are shown below, with Apidima 2 at top. Both are pretty badly banged up.

(All figure captions are from the Nature paper).

a–c, Apidima 2. a, Frontal view. b, Right lateral view. c, Left lateral view. d–f, Apidima 1. d, Posterior view. e, Lateral view. f, Superior view. Scale bar, 5 cm.

Because the skulls were so incomplete, their shapes had to be determined through reconstruction by computed tomography; and for Apidima 1, which has no face at all, the rear of the skull was reconstructed by making a mirror image of the better-preserved half. This fragmentary nature of Apidima 1 has to be kept in mind when assessing what it was.

The take-home lesson from the paper is that the dating and structural studies (done through uranium series analysis) shows that Apidima 2 falls well within Neanderthal types, but Apidima 1 shows features that lead the authors to conclude that it is indeed sapiens.  These sapiens features include a more rounded rear of the cranium as well as the lack of a characteristic Neanderthal trait, a bulge at the back of the skull like a bony hair bun. As the authors say, using morphological argot that you can skip (I’ve eliminated references in the paragraph below):

By contrast, Apidima 1 does not have Neanderthal features; its linear measurements fall mainly in the region of overlap between taxa. It lacks a Neanderthal-like rounded en bombe profile in posterior view. The widest part of the cranium is relatively low on the parietal; the parietal walls are nearly parallel and converge only slightly upwards, a plesiomorphic morphology that is common in Middle Pleistocene Homo. It does not show the occipital plane convexity and lambdoid flattening associated with Neanderthal occipital ‘chignons’. Rather, its midsagittal outline is rounded in lateral view, a feature that is considered derived for modern humans . The superior nuchal lines are weak with no external occipital protuberance. In contrast to some Middle Pleistocene specimens, the occipital bone is not steeply angled and lacks a thick occipital torus. A small, very faint, depression is found above the inion  Although suprainiac fossae are considered derived for Neanderthals, similar depressions occur among modern humans and in some African early H. sapiens. The Apidima 1 depression does not present the typical Neanderthal combination of features. It is far smaller and less marked even than the ‘incipient’ suprainiac fossae of MPE specimens from Swanscombe and Sima de los Huesos, and is closest in size to the small supranuchal depression of the Eliye Springs cranium, a Middle Pleistocene African (MPA). Apidima 1 therefore lacks derived Neanderthal morphology, and instead shows a combination of ancestral and derived modern human features.

The placement of Apidima 1 with sapiens and Apidima 2 with Neanderthals is shown in the following two graphs, where known fossils are grouped and identified with dots of various shapes. In the following, “modern” sapiens are blue triangles, Neanderthals are red stars, Middle Pleistocene Eurasians are yellow squares, and Middle Pleistocene Africans (presumably sapiens) are purple squares. The two axes represent various “principal components” that capture combinations of shapes and measurements that help distinguish specimens.

“Rec 1-4” are the reconstructions of Apidima 2. As you see, they fit pretty nicely within Neanderthals, or are closer to them than they are to sapiens (blue polygons). This is why Apidima 2 is considered a Neanderthal skull.

a, Analysis 1. PCA of Procrustes-superimposed facial landmarks, PC1 compared to PC2. H. sapiens, blue triangles (n = 19); Neanderthals, red stars (n = 6); MPE, yellow squares (n = 3); MPA, purple squares (n = 3). b, Analysis 2. PCA of Procrustes-superimposed neurocranial landmarks and semilandmarks, PC1 compared to PC2. H. sapiens (n = 25), Neanderthals (n = 8), MPE (n = 3), MPA (n = 5); Apidima reconstructions, black polygons, Apidima reconstruction mean configuration, black star. Wireframes below the plots illustrate facial and neurocranial shape changes along the PC1 of each analysis, respectively. Specimen abbreviations can be found in Supplementary Table 9. See Methods for detailed descriptions of analyses 1 and 2.

Here is Apidima 1, which is labeled as a diamond symbol in both left and right. As you see, it falls within the sapiens parameters and isn’t near the shape of Neanderthal skulls (red stars).

a, Analysis 3. PCA of Procrustes-superimposed neurocranial landmarks and semilandmarks, PC1 compared to PC2. H. sapiens (n = 23), Neanderthals (n = 6), MPE (n = 4), MPA (n = 5). b, Analysis 4. PCA of Procrustes-superimposed midsagittal landmarks and semilandmarks, PC1 compared to PC2. H. sapiens (n = 27), Neanderthals (n = 10), MPE (n = 5), MPA (n = 6).Wireframes below and next to the plots illustrate neurocranial and midsagittal shape changes along PC1 (analyses 3 and 4), and PC2 (analysis 4). c, Neurocranial shape index (analysis 3). Violins show the minimum–maximum range, boxes show the 25–75% quartiles and lines indicate the median. Modern Africans, green dots (n = 15); all other samples and symbols as in a and Fig. 2. See Methods for detailed descriptions of analyses 3 and 4.

Finally, here’s a different analysis that places both Apidima 1 (black triangle) and reconstructions of Apidima 2 (“Rec 1-4”) on one plot. Apidima 1 is close to “modern sapiens” (blue polygon(, but falls between it and early H. sapiens from Africa (purple polygon), demonstrating that, while sapiens-like, it wasn’t fully “modern” in its morphology.

Apidima 2 falls squarely within the ambit of Neanderthal skulls (red stars).

Analysis 5. PCA of Procrustes-superimposed neurocranial landmarks and semilandmarks shared between Apidima 1 and Apidima 2, PC1 compared to PC2. H. sapiens (n = 23), Neanderthals (n = 6), MPE (n = 4), MPA (n = 5). Wireframes below and next to the plot illustrate shape changes along PC1 and PC2. Symbols as in Fig. 2.

So there you have it: decent but not wholly convincing evidence that sapiens had already left Africa 210,000 years ago, and lived in the same period and place as Neanderthals. That’s a long time before we thought, and constitutes a dramatic revision of how we thought humans moved about in the last few thousand years.

A couple of questions remain:

How reliable is this conclusion? Well, I’m not a paleontologist, so I won’t put a definitive imprimatur on this diagnosis. In his News & Views piece, Eric Delsen notes that “Given that the Apidima 1 fossil and those from Misliya and Zuttiyeh (latter from Israel) are only partial skulls, some might argue that the specimens are too incomplete for their status as H. sapiens [JAC: they mean “modern H. sapiens”] to be certain. Delsen suggests that “paoleoproteomics”—sequence analysis of ancient proteins from the skulls—might help resolve this issue, even if DNA isn’t available.

Chris Stringer, one of the paper’s authors, issued a tweet that Matthew retweeted, praising it for its rigor and scrupulous honesty (Stringer says the reaction should be “a healthy skepticism”):

Did these early-emerging sapiens have contact with Neanderthals? Perhaps, though the dates of the two skulls are 40,000 years apart. But there is evidence for a long persistence of Neanderthals in Greece, so it’s likely that the two subspecies did coexist in the same general area. But if they mated with each other, there are no traces of that Neanderthal DNA in modern humans, which helps answer the next question:

If this fossil is indeed sapiens, what happened to the population? The authors suggest that the sapiens population simply died out without issue, and that’s supported by genetic data suggesting that all modern humans descend from an egress from Africa about 60,000 years ago. The Greek population may have simply gone extinct by attrition, or may have been wiped out by Neanderthals. Who knows? But if they died out without issue, as is likely, they are not our direct ancestors.

As Steve Gould used to say, when he taught human evolution every year he simply dumped his previous year’s teaching notes in the trash and wrote an entirely new lecture. That may have been an exaggeration, but shows how rapid the pace of understanding human evolution was. And still is! Given the paucity of finds in the genus Homo, there are many surprises to come.

_____________

Harvati, K., C. Röding, A. M. Bosman, F. A. Karakostis, R. Grün, C. Stringer, P. Karkanas, N. C. Thompson, V. Koutoulidis, L. A. Moulopoulos, V. G. Gorgoulis, and M. Kouloukoussa. 2019. Apidima Cave fossils provide earliest evidence of Homo sapiens in Eurasia. Nature, online.

Ideology versus science (again): University of New South Wales urges professors to lie about the arrival date of Aboriginals

June 30, 2019 • 10:30 am

A reader sent me a link to an article from The Australian which, sadly, is behind a paywall (click on screenshot to see). It is the very height of shameless pandering to ethnic groups who accept false stories about their history, and it’s also the nadir of academic truth. (If you want a transcript of the entire piece, judicious inquiry will yield one.)

 

For you, dear readers, I’ll transcribe the relevant parts:

University science lecturers have been warned off making the familiar statement in class that “Aboriginal people have been in Australia for 40,000 years.”

It puts a limit on the occupation of Australia and many indigenous peoples see this as “inappropriate,” according to the University of NSW language advice for staff.

The document suggests that it is “more appropriate” to say that Aborigines have been here since the beginning of the “Dreaming/s” because this “reflects the beliefs of many indigenous Australians that they have always been in Australia from the beginning of time, and came from the land.”

. . . A new set of classroom guidelines, which alert scientists to existing language advice, was circulated in the science faculty this month. One scientist said that most academics got on with their work and did their best to ignore such documents.

. . . The indigenous language advice says putting a date on Aboriginal arrival “tends to lend support to migration theories and anthropological assumptions.”

ASSUMPTIONS? But wait—there’s more!

Many indigenous Australians see this sort of measuring and quantifying as inappropriate.”

Asked for evidence, a UNSW spokeswoman cited “extensive consultation” with the university’s Centre for Indigenous Programs, Nura Gili, and its Equity Diversity & Inclusion Division.

But scientists push back, recognizing that although some aboriginal people hold this false view of their origins, the scientific facts say otherwise:

Last year a UNSW science faculty research centre said the First People “arrived soon after 50,000 years ago, effectively forever, given that modern human populations only moved out of Africa 50,000-55,000 years ago”.

The centre’s blog on its review of the scientific evidence begins: “Many Aboriginal Australians would say with conviction that they have always been here.”

. . . The inclusivity guidelines, which introduce and link to the indigenous language advice, were approved by a working group involving the dean Emma Johnston.

. . . The Weekend Australian asked researchers in this field whether indigenous Australians had warned them against the attempt to unravel the timing and sequencing of arrival on the continent. University of Wollongong archaeologist Richard Fullagar said: “The Aboriginal people I’ve worked with are enormously interested in the scientific evidence” of early indigenous occupation.

He said this research could be sensitive, and said: “Aboriginal people have sometimes told me that they have been here forever.

“Current scientific evidence indicates that the first Aboriginal groups in Australia came from islands to the north and ultimately (like all of us) from modern human dispersals out of Africa with subsequent genetic mixing.

The “advice” of UNSW, a respected Australian University, is reprehensible, for it urges scientists to dissimulate about where Australia’s inhabitants came from to protect their feelings and avoid contradicting their origin myths.  But it’s too bad if people’s feelings are hurt by the truth, especially when the truth is an important part of anthropology and history.

It is as if, in America, anthropology and evolution professors were told to avoid saying that hominins evolved from our common ancestor with chimpanzees beginning about six million years ago. After all, such a statement would hurt the feelings of the 38% of Americans who adhere to young-Earth creationism as described in Genesis. And surely that is a higher percentage of Americans than of aboriginals in the Australian population.

In an issue like this, there can be no compromise with truth, no catering to the false beliefs of minority groups. It’s doubly shameful that this initiative came in part from Dean Emma Johnston, who has a background in estaurine science.

But science is not a form of postmodernism in which all truths are equal. And a truth universally acknowledge by those who have studied the data is that the ancestors of indigenous Australians came to the continent roughly 50,000 years ago.

Shame on you, University of New South Wales and Dean Johnston! I hope, and trust, that the University scientists will ignore your ridiculous guidelines.

I’ll be sending a polite note to Dr. Johnston, whose contact details are at the link.

Human Phylogeography: The lessons learned, 1

June 4, 2019 • 9:10 am

by Greg Mayer

UPDATE. A couple of readers have drawn attention to the website, gcbias, of Graham Coop, a population geneticist at UC Davis. He has excellent discussions, with nice graphics, of issues in genetic genealogy, including calculation of the number of “genetic units” in particular generations. As an example, 7 generations back you have 256 ancestors, but only 286 genetic units produced by recombination, so although, on average, you will have a chunk from each of those 256, it is entirely plausible to have zero (since inheritance is stochastic). It’s well worth browsing, and this and this are good places to start. (Thanks to rich lawler and S. Joshua Swamidass for the pointers.)

In February, I posted the syllabus for a seminar class entitled “Human Phylogeography” that I was teaching with my colleague Dave Rogers. The seminar was based primarily on a close reading of David Reich’s (2018) Who We Are and How We Got Here (published by OUP in the UK). Well, the class has concluded now, and so I thought I’d report back on what happened.

First, I’d like to say that the class was a success. We had 16 students, double the most I’ve ever had in a number of similar seminar courses over the years, and the students were very successful in engaging with the subject in both written and oral contributions to the class. One of the students was a history major, and towards the end of the semester a colleague in computer science mentioned that, quite coincidentally, he was reading the book, so he joined the class for the last few meetings. In many ways, it was what college is supposed to be like (though too often isn’t). I hope the students learned a lot. I did, and here is the first of the three most striking things I learned.

1. Recombination is a lot rarer than you think.

If you think back to the last time you studied genetics, you’ll recall the phenomenon of recombination, one aspect of which is crossing over. Crossing over occurs during meiosis. Chromosomes come in homologous pairs (23 pairs in humans, for 46 total), and in meiosis the homologues can exchange pieces with one another. The chromosomes physically touch and cross one another, which is observable under the microscope, and are called, appropriately enough, chiasmata (chiasma, sing.)

Image result for crossing over meiosis
From BioNinja, https://ib.bioninja.com.au/standard-level/topic-3-genetics/33-meiosis/crossing-over.html

Recombination is important for a variety of reasons (for one, it increases genetic variability), but for our current purposes its importance is that it breaks up the nuclear genome from 23 genetic units into more, and smaller, units (as opposed to the mitochondrial genome, which has a number of genes, but all are inherited as a single genetic unit, since there is no recombination in mitochondria). In humans, it turns out, there are only 1-2 crossovers per chromosome per generation (1.2 per chromosome in fathers, 1.8 in mothers).

Now, I’d always thought that crossing over occurred frequently enough that we could think of the genome as essentially infinitely divisible. (There are 3 billion base pairs in the human genome, so, in the limit, there would be 3 billion genetic units, so not quite infinite!) But, it turns out that crossovers occur sufficiently infrequently that there is an appreciable chance that, if you go enough generations back, you share NO genes with your ancestor. This is because the number of ancestors goes up fast (2, 4, 8, 16, 32, 64, 128, 256, etc.), but the breaking up of the genome into smaller units by crossing over isn’t fast enough to ensure that the probability of sharing nothing is near zero.

Here’s a figure from Reich’s book showing how blocks of genes are broken up by recombination.

From Reich, 2018.

You start with an entirely Neanderthal chromosome (dark), which enters the anatomically modern human population by hybridization. A few generations later, the Neanderthal chromosome has been broken up, but it still occurs as largish blocks amongst the anatomically modern sections (gray). Still later, the blocks are smaller and fewer. (We’re assuming continued backcrossing into the anatomically modern population, so the % Neanderthal decreases; there could also be selection causing changes in the frequency of Neanderthal alleles). Finally, a present day individual has his Neanderthal DNA broken up into even smaller bits.

Here’s a figure from a talk by Svante Pääbo, showing in the top row for each chromosome (there are 22 listed, from 1-22) the entire genome of “Oase Boy” from 40K years ago in Romania. The green lines are Neanderthal sites in his genome. The five rows below Oase Boy are five modern human individuals; the colored lines are their “Neanderthal bits”. Note that for each chromosome, Oase boy has the biggest block of Neanderthal genes (green fluorescece):

From Pääbo , 2018. (Click to enlarge.)

Because of the age of the Oase sample, some of the black lines are missing data, and so Pääbo infers that there are seven large continuous blocks of Neanderthal genes (yellow bars above the Oase Boy line). Note that the modern individuals have less Neanderthal DNA, and it is not in large blocks.

Because the size of the blocks breaks up in a statistically predictable fashion, you can get a “recombination clock“, so that based on the size of the blocks you can estimate how many generations ago the hybridization occurred. For Oase Boy, Pääbo estimated that his Neanderthal ancestor occurred 4-6 generations back (his great great, or great great great, or great great great great grandfather).

From Pääbo , 2018, showing Oase’s Neanderthal ancestor (red) in the 5th generation (it could also be in the 4th or 6th).

Because the placement and frequency of crossing over is stochastic (random), the situation must be statistically modeled to derive sound estimates, and there will be a range of plausible estimates. And, since some of the fossils are well dated by other means, we can also estimate the long term human generation time, as was done by Priya Moorjani and her colleagues: it’s 26-30 years.

So, the low rate of recombination allows us to construct a “recombination clock”, and to estimate generation times. This is great stuff!

It also solved for me what was a puzzle. You may recall that last year Elizabeth Warren released the results of DNA tests showing that she had American Indian ancestry several generations back. This essentially confirmed what her family’s oral history said. The amount of her Indian ancestry was small (less than 1%), and a range of generations (6-10) was provided by the analysis (as was done by Pääbo for Oase Boy).

Now, there are a number of ways which these ancestry tests can be criticized, one of the most difficult for them being that there are very few North American Indian genotypes in the database used, and thus “American Indian” relationship is indicated by relationship to Central and South American Indians. Some critics of Warren, however, made erroneous criticisms. She did not contend, as some accused her of, of saying the results showed she was Cherokee—with few if any Cherokee in the database, the ancestry tests could not determine this. (And tribal membership is a legal matter, anyway, not directly dependent on genetic similarity.)

But some critics said that the data were consistent with her having no Indian ancestry at all. I wondered how they could say that– there are 3 billion bp, and 1 % of that is still a very large number. But now I realize my error. There are very many fewer genetic units– more than 23, but a lot less than 3 billion!– due to low rates of recombination. And, because of this, if you go back several generations, there is an appreciable probability of sharing no DNA with an indubitable ancestor. I now believe the critics must have looked at the latter fact, and realized Warren may not have DNA from all of her ancestors, and thus suggested she may have no Indian ancestry. But their error is that in saying she may lack DNA from an ancestor, say, 8 generations back, they are invoking an a priori probability. But in Warren’s case, her DNA was examined, and showed that she did have Indian ancestry.

Gravel, S. 2012. Population genetic models of local ancestry. Genetics 191:607-619. pdf

Ho, S. Y., Chen, A. X., Lins, L. S., Duchêne, D. A., & Lo, N. 2016. The genome as an evolutionary timepiece. Genome Biology and Evolution 8: 3006–3010. pdf

Huff, C.D. et mult. 2011. Maximum-likelihood estimation of recent shared ancestry (ERSA). Genome Research 21:768-774. pdf

Moorjani P, Sankararaman S, Fu Q, Przeworski M, Patterson N, Reich D. 2016. A genetic method for dating ancient genomes provides a direct estimate of human generation interval in the last 45,000 years. Proceedings of the National Academy of Sciences USA 113:5652-7. pdf

Pääbo, Svante. 3 October 2018. A Neanderthal Perspective on Human Origins. (video: embedded below)

Reich, D. 2018. Who We Are and How We Got Here: Ancient DNA and the New Science of the Human Past. Pantheon, New York.