Sex with a stranger? Evolutionary psychology and sex differences in behavior

June 6, 2021 • 9:15 am

In the early days of evolutionary psychology—that is, when it was just beginning to be applied to humans—I was rather critical of the endeavor, though not so much about “sociobiology”, the application of evolutionary principles to animal behavior. A lot of the early evo psych stuff on humans was weak or overly speculative.

Since then, I’ve mellowed somewhat in light of replicated research findings about human behavior that show phenomena predicted by or very consistent with the theory of evolution. Not only are the phenomena predicted and replicated, but they are in line with what other animals show. Further, researchers have also falsified some alternative explanations (“culture” or “patriarchy” is the most common one).

I’ll add here that the disturbingly common claim that evolutionary psychology is “bogus” or “worthless” as an entire field is ridiculous, both in principle and in practice. In principle, why should human behavior, or behavioral differences between the sexes, be the one area that is exempt from evolutionary influence, especially given that we evolved in small hunger-gatherer groups for at least five million years, on top of which is overlaid a thin veneer (about 20,000 years) of modern culture? That position—that all differences between men and women, say, are due to cultural influence—is an ideological and not an empirical view. If physical differences, both between sexes and among groups, are the result of evolution, why not mental ones? After all, our brain is made of cells just like our bodies!

In practice, there are several types of human behavior that, using my mental Bayes assessment, I consider likely to reflect at least some of the workings of evolution, past and present, although culture may play a role as well. There will be an upcoming paper on these fairly solid evo-psych behaviors (I’m not an author), but I’ll highlight it when it’s published.

In the meantime, we have one behavior, described in this 2017 article from Areo Magazine, that describes a “universal human behavior” involving sex differences, and a behavior that’s likely to reflect our evolutionary heritage. Although the article is four years old, it’s worth reading. The author, David P. Schmitt, has these bona fides:

David P. Schmitt, PhD, is Founding Director of the International Sexuality Description Project, a cross-cultural research collaboration involving 100s of psychologists from around the world who seek to understand how culture, personality, and gender combine to influence sexual attitudes and behaviors.

See also his Wikipedia page, which describes him as “a personality psychologist who founded the International Sexuality Description Project (ISDP). The ISDP is the largest-ever cross-cultural research study on sex and personality.”

The article, which I recommend you read, is chock-full of data. Click on the screenshot for a free read:


The behaviors Schmitt discusses in this longish but fascinating and readable piece are summarized in the first two paragraphs (there are lots of references should you want to check his claims):

Choosing to have sex with a total stranger is not something everyone would do. It probably takes a certain type of person. Quite a bit of evidence suggests, at least when it comes to eagerly having sex with strangers, it might also take being a man. Let’s look at the evidence.

Over the last few decades almost all research studies have found that men are much more eager for casual sex than women are (Oliver & Hyde, 1993; Petersen & Hyde, 2010). This is especially true when it comes to desires for short-term mating with many different sexual partners (Schmitt et al., 2003), and is even more true for wanting to have sex with complete and total strangers (Tappé et al., 2013).

Of course this is “common wisdom” in American culture: it is the heterosexual guy who does the pursuing, and does so without many criteria beyond the lust object having two X chromosomes, and he’s still often rejected, while women are far choosier about who they mate with.

There are many studies, described and cited by Schmitt (usually using lab experiments or good-looking students on campus approaching members of the opposite sex) that show the same thing. An attractive man propositioning a woman for sex is accepted about 0% of the time, while, in the opposite situation far more than half the males accept a sexual proposition from an attractive female stranger. Here are two studies, but there are more:

In a classic social psychological experiment from the 1980s, Clark and Hatfield (1989) put the idea of there being sex differences in consenting to sex with strangers to a real life test. They had experimental confederates approach college students across various campuses and ask “I’ve been noticing you around campus, I find you to be very attractive, would you go to bed with me tonight?” Around 75 percent of men agreed to have sex with a complete stranger, whereas no women (0 percent) agreed to sex with a complete stranger. In terms of effect size, this is one of the largest sex differences ever discovered in psychological science (Hyde, 2005).

Twenty years later, Hald and Høgh-Olesen (2010) largely replicated these findings in Denmark, with 59 percent of single men and 0 percent of single women agreeing to a stranger’s proposition, “Would you go to bed with me?” Interestingly, they also asked participants who were already in relationships, finding 18 percent of men and 4 percent of women currently in a relationship responded positively to the request.

This of course jibes with the behavior of many animals (in my flies, for example, males will court almost any female, even wooing pieces of dust or small blobs of wax), while females repeatedly reject males. It’s true of primates in general, and of many animal species. And it makes evolutionary sense. If a male mates with five females instead of one, he’s likely to have five times more offspring. In the reverse situation, though, a female who mates with five males in a short period will have roughly the same number of offspring as if she mated just once. That’s because she makes a huge investment in eggs and (in some species like ducks) maternal care, and so she should be selected to be choosy about her mates, looking for a male who is fit, healthy, may have good genes, and, if there’s parental care, will be an attentive father. Since the male has far less to lose, and far more to gain, by repeatedly mating with different females, this explains the strategy of “wanton male versus choosy female” sexual preference. These are likely to be evolved sexual behaviors.

This of course is a generalization. There are certainly picky men and women who are less choosy about their partners. But it’s a generalization that holds up not only in the “choice” studies I just mentioned, but in other aspects as well. Psychological studies show that (here I quote Schmitt, bolding is his)

. . . men have more positive attitudes towards casual sex than women, have more unrestricted sociosexuality than women, and generally relax their preferences in short-term mating contexts (whereas women increase selectivity, especially for sexual attractiveness.

. . . Cognitively and emotionally, men are more likely than women to have sexual fantasies involving short-term sex and multiple opposite-sex partners, men perceive more sexual interest from strangers than women, and men are less likely than women to regret short-term sex or “hook-ups.”

Considering sexual fantasies, men are much more likely than women to report having imagined sex with more than 1,000 partners in their lifetime (Ellis & Symons, 1990).

Behaviorally, men are more likely than women to be willing to pay for short-term sex with (male or female) prostitutes, men are more likely than women to enjoy sexual magazines and videos containing themes of short-term sex and sex with multiple partners, men are more likely than women to actually engage in extradyadic sex, men are more likely than women to be sexually unfaithful multiple times with different sexual partners, men are more likely than women to seek one-night stands, and men are quicker than women to consent to having sex after a very brief period of time (for citations, see Buss & Schmitt, 2011).

Here’s a table reproduced in the Areo paper taken from Buss and Schmitt (2011), where you can find the original references. Click to enlarge.

These patterns hold in nearly all studies in different parts of the world. That in itself suggests that culture may play an insignificant role in the difference I’m discussing.

Now if you’re thinking hard, you can think of at least four non-evolutionary explanations for these behaviors (I’ve combined disease and pregnancy in #3 below). Both, however, have been shown to be unlikely to be the major explanation for the sex difference in choosiness.

1.) Patriarchy: These could be cultural differences enforced by the patriarchy and socialization. Why a patriarchy exists itself may be evolutionary (e.g., males are stronger and thus can control females more easily than the other way around), but male dominance itself is not the explanation we’re testing here. Schmitt explains why (beyond observed cultural universalism), this is unlikely to explain the entire behavioral difference (all emphases are the author’s):

For instance, Schmitt (2015) found sex differences in the sociosexuality scale item “I can imagine myself being comfortable and enjoying ‘casual’ sex with different partners” were largest in nations with most egalitarian sex role socialization and greatest sociopolitical gender equity (i.e., least patriarchy, such as in Scandinavia). This is exactly the opposite of what we would expect if patriarchy and sex role socialization are the prime culprits behind sex differences in consenting to sex with strangers.

How can this be? Why are these sex differences larger in gender egalitarian Scandinavian nations? According to Sexual Strategies Theory (Buss & Schmitt 1993), among those who pursue a short-term sexual strategy, men are expected to seek larger numbers of partners than women (Schmitt et al., 2003). When women engage in short-term mating, they are expected to be more selective than men, particularly over genetic quality (Thornhill & Gangestad, 2008). As a result, when more egalitarian sex role socialization and greater sociopolitical gender equity “set free” or release men’s and women’s mating psychologies (which gendered freedom tends to do), the specific item “I enjoy casual sex with different partners” taps the release of men’s short-term mating psychology much more than it does women’s. Hence, sex differences on “I enjoy casual sex with different partners” are largest in the most gender egalitarian nations.

Overall, when looking across cultures, reducing patriarchy doesn’t make these and most other psychological sex differences go away, it makes them larger (Schmitt, 2015). So much for blaming patriarchy and sex role socialization.

2.) Fear of injury. In general, men are stronger than women (this is almost surely the result of evolution affecting competition for mates). Perhaps women are leary of accepting propositions from unknown men because they might get hurt, as do many prostitutes. But several studies show that safety alone cannot be the whole explanation:

Clark (1990) was among the first to address the issue of physical safety. He had college-aged confederates call up a personal friend on the phone and say “I have a good friend, whom I have known since childhood, coming to Tallahassee. Joan/John is a warm, sincere, trustworthy, and attractive person. Everybody likes Joan/John. About four months ago Joan/John’s five year relationship with her/his high school sweetheart dissolved. She/he is was quite depressed for several months, but during the least month Joan/John has been going out and having fun again. I promised Joan/John that she/he would have a good time here, because I have a friend who would readily like her/him. You two are just made for each other. Besides she/he has a reputation as being a fantastic lover. Would you be willing to go to bed with her/him?” Again, many more men (50%) than women (5%) were willing to have sex with a personally “vouched for” stranger. When asked, not one of the 95% of women who declined sex reported physical safety concerns were a reason why.

3.) Fear of pregnancy and/or disease. Since venereal diseases can be passed in both directions, I’m not sure that disease is a good explanation, though perhaps women are more likely to get serious disease than are men. As far as pregnancy is concerned, there’s at least one study showing it can’t be the sole factor:

Surbey and Conohan (2000) wondered whether worries of safety, pregnancy, stigma, or disease were what was holding women back from saying yes to sex with a stranger. In a “safe sex” experimental condition, they asked people “If the opportunity presented itself to have sexual intercourse with an anonymous member of the opposite sex who was as physically attractive as yourself but no more so (and who you overheard a friend describe as being a well-liked and trusted individual who would never hurt a fly), do you think that if there was no chance of forming a more durable relationship, and no risk of pregnancy, discovery, or disease, that you would do so?” On a scale of 1 (certainly not) to 4 (certainly would), very large sex differences still persisted with women (about 2.1) being much less likely to agree with a “safe sex” experience with a stranger compared to men (about 2.9).

So, sex differences in agreeing to sex with strangers are not just a matter of safety issues, pregnancy concerns, slut-shaming stigma, or disease avoidance. Controlling for all of that, researchers still find large sex differences in willingness to have sex with a stranger.

There’s a lot more in this paper, including Schmitt’s critique of the two papers cited widely as disproving the “pickiness” hypothesis. Both papers, however, suffer from extreme methodological flaws, and in both cases the results support the “pickiness” hypothesis when the flaws are corrected.

You can read the hypothesis and judge for yourselves, but I think this is one of the best examples we have of evolutionary psychology explaining a difference between men and women in behavior*. As I said, it’s shown up throughout the world in different cultures, it’s paralleled in many species of animals, alternative explanations fail to explain the data, other, unrelated data support at least a partial evolutionary basis of the choice difference, and the few papers that claim to disprove it wind up actually supporting it.

Aside from “universal” behavior like sleeping, eating, or wanting to reproduce, which are surely instilled in us by evolution (and nobody questions those), we shouldn’t ignore differences between groups, especially the sexes, as having an evolutionary origin. It’s likely that morphological differences between geographic populations, like the amount of melanin in the skin, are adaptive responses to natural selection, so why is behavior the one trait that is always off limits to evolutionary explanation?  It’s ideology, Jake.

h/t: Steve Stewart-Williams


*As a reader points out below, and even more obvious evolutionary difference is that the vast majority of men are sexually attracted to women, and vice versa. That would be hard to explain as a result of the patriarchy or of socialization.

Why do backs itch so much?

January 31, 2021 • 12:00 pm

A while back, someone gave me a Chinese backscratcher: a piece of bamboo with a hand carved at the end with slightly separated fingers.  I use it every couple of days when my back works up a good itch, and believe me, it provides substantial relief!  Here’s what mine looks like:

But when I use it I’ve pondered two questions.

A.) Is the relief you get when scratching your back pleasure, or simply the removal of discomfort? (Or are they equivalent?) This same question applies when you finally make it to the restroom after having to hold your bowels or bladder for a long time. I wonder if philosophers have debated this question.

B.) Why do backs itch so much? I have two theories here, which are mine. The first is that they itch no more than do fronts (i.e., your chest), but we’re unconsciously scratching our fronts all the time, while we can’t reach our backs without a special implement. But I don’t notice myself scratching my chest.

The other is that dirt and oils accumulate on your back more than they do on your front, simply because you can’t reach your back so easily in the bath or shower. I don’t have a sponge on a stick or anything like that, and so am forced to wash my back by reaching around with a piece of soap. I’m never sure that does a great job because it’s hard to reach all the places.  If any accumulated back schmutz makes you itch, this could be an explanation.

Maybe there are other theories as well, but these are the only two I’ve thought of.

Why your eyes can rotate: an evolutionary explanation

September 26, 2020 • 2:30 pm

Reader Bryan sent me a link to this video by Steve Mould discussing how our ability to rotate our eyes may be an exaptation (and a vestigial remnant) from ancestors who had eyes on the sides of their head. It’s a fascinating idea, and may well be true. Or, to quote the YouTube notes:

Torsional eye movement, known as cycloversion and cyclovergence have a fascinating evolutionary history via our evolutionary ancestors that had eyes on the sides of their heads. Your eyes twist in this way whenever you tilt your head!

After 10:07 there are ads, so you may wish to skip the last two minutes of the video.

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.


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).

Note and correction on the “Lewontin fallacy”

April 23, 2020 • 1:00 pm

Yesterday I wrote about Angela Saini’s misguided claim that human populations and races (I prefer “ethnic groups” rather than “races”) are basically genetically identical. So identical, in fact, that, as Saini argued, it’s entirely possible (or even likely) that the genomes of a South Asian and a white Canadian could be more similar than the genomes of two South Asians. That is wrong, but plays into Saini’s ideological bias that there are no appreciable or meaningful difference between biological races.

As I indicated, we now have sufficient data to show that the chances that her assertion is true is close to zero. Looking at the whole genome, you’re not going to find many South Indians whose DNA is more similar to that of a white Canadian than to that of another South Asian.

In trying to understand why Saini would make such a statement, I speculated that she had bought into the “Lewontin fallacy“: the claim by my ex Ph.D. advisor that the vast bulk of genetic variation segregating in our species occurs among individuals within populations, rather than among populations within a classically-defined “race” or among races.

From his mathematical analysis, Lewontin concluded that the term “race” has no biological reality. The error of Lewontin’s claim was pointed out by geneticist A.W.F. Edwards, who noted that Lewontin was treating each gene as independent. But they’re not, because the constraints of history, geographic separation, and evolution ensures that differences among populations and races at different genes are correlated. Taking these correlations into account, Edwards concluded this (characterized in Wikipedia):

In Edwards’ words, “most of the information that distinguishes populations is hidden in the correlation structure of the data.” These relationships can be extracted using commonly used ordination and cluster analysis techniques. Edwards argued that, even if the probability of misclassifying an individual based on the frequency of alleles at a single locus is as high as 30 percent (as Lewontin reported in 1972), the misclassification probability becomes close to zero if enough loci are studied.

And the use of cluster analysis is in fact the way that population-genetic studies are able to describe evolutionary history and ancestry from DNA data. I cited cluster analysis of the genetic structure of the British Isles as an example of how well one can deduce someone’s ancestry and geographic origin from looking at half a million base pairs—a small fraction of the total DNA in the human genome (about 0.02%).

I stand by my claim that Saini was wrong, but I did err on one count, one that doesn’t affect my conclusions but that I wanted to point out to be scientifically accurate.

And that is this: Lewontin’s original claim about the apportionment of genetic variation among individuals, populations, and races was incorrect. This was pointed out to me by reader, biologist, and polymath Lou Jost, who works at a field station in Ecuador. I vaguely remembered that Lou had done some work on this, but had forgotten, as he just reminded me, that work completely invalidates Lewontin’s method.

Lou has written several papers on this error, one of which you can access for free. (I have the other papers if you want the pdfs.) Click on the screenshot:

The math behind Lou’s arguments is above the pay grade of many of us (including me), but I, at least, am convinced that Lewontin was wrong for reasons beyond Edwards’s claim: he was wrong because, as Lou showed, he “used a measure of ‘differentiation’ that doesn’t really measure differentiation.” Lou presented an alternative diversity-based model that will allow you to compare differentiation within and among groups (this holds for species diversity in ecology as well as genetic diversity in and among populations), but he didn’t apply it to Lewontin’s data, because those data are outmoded now (they were based on electrophoretically derived allele frequencies).

The take-home lesson is that Lewontin’s conclusion is wrong not only because it applies to single loci assumed to be uncorrelated, but also because he used the wrong metric to compare within- versus between-group diversity. As Lou noted, the take-home lesson of Lewontin’s paper—that most of the genetic diversity in our species is present in any population of our species, with only smaller amounts added by looking at different populations or races—may still be right. But until Lou’s metrics are applied to the new and better data we have, we just won’t know.

Again, this correction affects an idea that I thought Saini might have been erroneously pondering when she made her misleading statement. It does not affect the fact that her statement is misleading, and that we really can distinguish populations and ethnic groups very well using genetic data—the more data the better. And it doesn’t affect my claim that Saini is either deliberately misleading people or is ignorant about the data on population differentiation in our species, and that her ignorance, willful or not, plays into her ideological narrative about “races.”

I stand corrected on the Lewontin issue, and thank to Lou Jost for setting me straight about the “Lewontin fallacy.”

Angela Saini misrepresents Galton kerfuffle at University College London; fails to see the beam in her own eye

March 15, 2020 • 10:30 am

Angela Saini is a British science writer who has two degrees: in Engineering from the University of Oxford and in Science and Security from King’s College London. She’s written three books:

Although I haven’t read any of these in full, I’ve read several of her essays and watched several of her videos, as well as having read criticism of her latest book, which is largely an indictment of science for trafficking in racism, some of it unrecognized. More about that in a minute.

Last week Saini wrote a one-page “World view” piece in Nature that I want to discuss and criticize. Click on screenshot below; or get a pdf here

Most of the article deals with a recent controversy in which a committee of employees, students, and staff from University of College London (UCL) investigated whether the name of Francis Galton, a famous statistician, biologist, and polymath, should be removed from UCL buildings and endowments. Why? Because Galton was an advocate of eugenics, and helped set up commissions, journals, and organizations to study it.

Although none of Galton’s work ever resulted in any eugenic activities involving breeding or prevention of breeding, or the creation of British laws or government policies, his advocacy of eugenics is  deemed sufficiently repugnant to warrant the creation of a UCL commission of inquiry whose task was to deal with how to erase Galton’s history. Most of the people on the commission weren’t scientists (there were a few), and there were a lot of people from diversity offices and the social sciences. Given that, the outcome was preordained.

I have a copy of the long report (ask and ye shall receive), which basically recommends that everything with the name of “Galton” on it be renamed. Further, there are recommendations that the University apologize (though it’s not clear to whom), and that everybody in UCL be given mandatory instruction about this shameful episode in the University’s history.

Saini makes two claims in her Nature piece.  First, that the reexamination of Galton’s history was prompted by “humanities scholars” rather than by the university’s biologists.  As we’ll see in a subsequent post, this claim is flatly wrong: UCL’s biologists have been teaching about Galton’s eugenic views for decades. Yes, humanities scholars were on the committee that decided to censor everything Galton did out of UCL history, but Saini’s claim below (in bold) is incorrect and disingenuous:

When a survey conducted as part of the UCL inquiry asked staff and students whether “we should separate science and politics”, it found agreement among higher percentages of those in the sciences and engineering than in the social sciences and history. In my coverage of the inquiry, I’ve seen that it was not the university’s biologists, but its humanities scholars — including curator Subhadra Das and historian Joe Cain — who forced their workplace to confront a sordid history that some geneticists had been willing to overlook.

There will be more on this as many UCL geneticists, including ones we’d consider liberal or woke, are taking violent exceptions to Saini’s claim above, as well as to the “erasure” of Galton that the committee recommended. When they speak out publicly, I’ll then write another piece.

As far as the “separation of science and politics” are concerned, that leads us to the second issue: Saini’s arrogant claim that we should all admit that we are not objective, even when we deal with science. All, that is, EXCEPT FOR SAINI, who apparently does not include herself in the list of “non-objective people.” Have a gander:

Scientists who imagine that bias lies in others, not themselves, fail to recognize that to live in the world today is to be drip-fed assumptions and prejudices that guide our thoughts and actions. If it were any other way, the demographics of academia would be more equitable, and the current strain of genetic determinism in governments wouldn’t be possible.

. . . Scientists rarely interrogate the histories even of their own disciplines. When I studied engineering at university, I was expected to write just one essay on ethics in four years. No wonder that new technologies perpetuate racial and gender stereotypes, or that automated facial recognition struggles to identify people with darker skin.

The best research is done not when we pretend that we are perfectly objective, but when we acknowledge that we are not. The UCL inquiry report recommends that students and staff be exposed to the history of eugenics, and that students be encouraged to value the history of their own fields. I would go further. Scientists need both history and the social sciences to develop the intellectual tools to think critically about their research and

What’s most curious about Saini’s self-exemption from The Biased is that she’s clearly biased: she’s uses Critical Race Theory in her analyses, is pretty much of a blank slater, and, from what I read in reviews (including direct quotes), and from what I’ve seen in her YouTube talks and interviews (e.g., here), she denies any usefulness of the term “race” (I avoid the term, too, but human populations are structured in biologically meaningful ways), and, most important, appears to have distorted and cherry-picked the biological literature on human differentiation to make the ideological point that differentiation isn’t particularly meaningful.  Further, she appears to have the attitude that finding any difference between races, whether physiological or, especially, psychological, would somehow buttress racism.

I’ve argued against that latter view repeatedly, saying that regardless what science shows—and I can’t deny that many scientists were biased and propped up racism with specious arguments—our moral view on the equality of people should not be based on biological facts. If that were the case, and you make Saini’s argument that we really are biologically equal in the most important ways, and that such a finding dispels racism, then you become liable to future studies that might show biological inequalities between groups. And that would then prop up racism. Moral equality should be a philosophical, not a biological argument, but Saini appears to believe (or at least behave) otherwise.

I’ve read several reviews of Saini’s latest book, and found the one below the most cogent and reasonable. Yes, it’s in Quillette, and I do take issue with a few of its clams, but it seems quite even-tempered and rational on how we should regard genetic differentiation in humans.  (I note that both authors were dismissed from their jobs for their work on race, yet I can’t see any grounds for dismissal from this review, at least.)

The long piece below pretty much damns Saini’s book, using direct quotes. Click on the screenshot to read it:

As I said, I take issue with a few of the authors’ claims. I haven’t read The Bell Curve, so I can’t speak to their argument that many scholars signed a petition defending the book. And I was pretty critical of Nicholas Wade’s book on race, “A Troublesome Inheritance,” which Winegard and Carl think was “unfairly condemned” (see my posts here and here.) But other claims, like Saini’s misunderstanding the “Lewontin Fallacy” committed by my Ph.D. advisor in defense of the genetic equality of races, are accurate, and make one realize how tendentious Saini’s claims really are. (Lewontin, god bless him, was also tendentious and wrong on several issues.)

It’s a long review and I’ll give only one quote.  This is about using science to prop up morality.

Finally, by far the most prominent fallacy in Superior, one which lies at the very heart of Saini’s book, is the fallacy of equating any claim that genes might contribute to population differences on non-“superficial” traits with racism. (For the sake of brevity, we shall refer to this as ‘the fallacy of equating hereditarian claims with racism.’) Indeed, this fallacy encompasses the third and fourth of the theses that we laid out in the introduction.

By way of illustration, Saini employs the terms “scientific racism” or “scientific racist” 17 times in the book, and she employs the terms “intellectual racism” or “intellectual racist” an additional 11 times. In Chapter 1 she describes the supposition that population groups “may have evolved into modern human beings in different ways” as “unconscionable.” And in Chapter 6, when discussing the work of famed geneticist Luigi Cavalli-Sforza, she writes, “as he saw it, racism was just a scientific idea that turned out to be incorrect.”

Before proceeding, we should be clear about what we are not saying. First, we are not denying that research into the genetics of human differences has been misused for appalling purposes at various points over the last two centuries. Second, we are not denying that some of the scientists who have undertaken such research were motivated by racial animus or by a desire to subjugate other people. Hence we understand the temptation to assume the worst about anyone who might be willing to entertain what we have called ‘hereditarian claims.’ Nonetheless, equating hereditarian claims with racism is a fallacy, and one that we believe is likely to end up doing more harm than good.

As Steven Pinker argued at length in his book The Blank Slate, those who equate testable scientific claims with various ‘isms’ (sexism, racism, fascism, etc.) are effectively holding our morals hostage to the facts. By using the word ‘racist’ to describe a claim such as ‘genes may contribute to psychological differences between human populations,’ they are implying that:

  • The claim must be false; but also that
  • If the claim were ever shown to be true, then racism would be “scientifically correct.”

Yet as Pinker notes, this is a complete non-sequitur:

I hope that once this line of reasoning is laid out, it will immediately set off alarm bells. We should not concede that any foreseeable discovery about humans could have such horrible implications. The problem is not with the possibility that people might differ from one another, which is a factual question that could turn out one way or the other. The problem is with the line of reasoning that says that if people do turn out to be different, then discrimination, oppression, or genocide would be OK after all.

The argument that we should not hold our morals hostage to the facts has been made over and over again by scholars interested in the genetics of human differences. As far back as the 1960s, one of the 20th century’s leading biologists, Ernst Mayr, said the following:

Equality in spite of evident non-identity is a somewhat sophisticated concept and requires a moral stature of which many individuals seem to be incapable. They rather deny human variability and equate equality with identity […] An ideology based on such obviously wrong premises can only lead to disaster. Its championship of human equality is based on a claim of identity. As soon as it is proved that the latter does not exist, the support of equality is likewise lost.

The market for woke books is huge, and you won’t get anywhere claiming that scientists should be studying genetic differentiation between sexes and races because it’s interesting (one must of course always be sensitive to how people feel about this). Ergo you can get away, as Saini has, with being deeply tendentious. A parallel is Cordelia Fine, whose books on gender always are supercritical of studies showing differences between males and females, but go easy on studies that claim the opposite (see my posts on her work here and here).

In view of Saini’s own ideological biases and tendentious treatment of the literature, it’s ironic that she chastises scientists for not recognizing their biases, while completely failing to recognize—or at least mention—her own. Or is she the only writer completely free of bias?. I have ordered her book and will read it, but I already discern from her essays and interviews, as well as excerpts from Inferior, that she is no less ideological than the so-called “nonobjective” scientists she criticizes.  The parable about motes and beams in one’s eye applies.

h/t: William L.

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:

“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.

You have mites on your face

May 22, 2019 • 11:30 am

As you sit there reading this, thousands of mites are living on your face, burrowed into the follicles of your facial hair and the pores around your eyes, nose, and mouth. As the NPR article below shows (click on second screenshot), every human is colonized by “eyelash mites”, members of the subphylum Chelicerata—yes, relatives of spiders and scorpions—in the species Demodex folliculorum. Here’s what they look like:


Read more about them here, watch the video below, or do both (they give different information):

They pretty much rest head down within the pores from which hairs arise (several mites per pore), coming out at night to mate and eat the grease that your face exudes. Gross, eh?

But you don’t notice them, as they’re innocuous and rarely cause problems. Occasionally they will get out of control, usually when your immune system is suppressed for some reason. This causes a white sheen called “Demodex frost”, which looks like this (it’s a particularly bad case). But it can be treated.


I find it interesting that this species, which is limited to Homo sapiens, is with us all of our lives, and does us no harm. I bet more than 95% of people don’t even know they have them. You’re not born with them; you acquire them from contact with others (most likely the mother) after you’ve exited the womb. And the good news is that they have no anus, so they don’t defecate on you. (They store their wastes for the duration of their short lives.)

Here’s a cool NPR video giving you more information about them. As expected, their low mobility means that they’ve become genetically differentiated among human populations, so you can tell where a mite came from by sequencing its DNA. It would be interesting to compare a phylogeny of human groups with that of their eyelash mites. If there is any “cross-group” movement, the phylogenies wouldn’t coincide.

Watch this, because these are on YOU!

How do we know that Neanderthals were nearly all right-handed?

October 25, 2018 • 12:00 pm

A while back I wrote about my visit to the Croatia Natural History Museum, where curator Dr. Davorka Radovčić kindly gave three of us a several-hour look at Neanderthal bones from the nearby location of Krapina, one of the most fruitful Neanderthal sites known. At the time I mentioned there was evidence that most Neanderthals were right-handed, but I didn’t really explain why. Now Davorka has sent me two papers (references and links below) that show how we know this. I’m going to write mostly about the Lozano et al. paper (free with the legal UnPaywall app), which tells the tale up to the present. If you can’t get either or both of these papers, email me and I’ll send them.

It is in fact true that about 90% of Neanderthals were right-handed, and that’s the same as present-day H. sapiens sapiens, even though Neanderthals aren’t really the ancestors of modern humans (we do, however, carry some of their genes). That probably means that the common ancestors of our two subspecies—I consider Neanderthals as H. sapiens neanderthalensis, a subspecies of H. sapiens—were also right handed. And indeed, chimpanzees (though not bonobos) are 49% right-handed and 29% left-handed, with 22% of individuals “ambiguous”.

But new data also shows that our ancient ancestors—before the split between modern H. sapiens and Neanderthals, were also right-handed. How did they do this?

It doesn’t come from looking at arm robustness in fossils, for that doesn’t work, nor does it come from looking at brains (as seen in crania), as that doesn’t work, either. It comes from looking at incision marks on the teeth made when a hominin is holding something in its mouth and cutting it—cutting it with the dominant hand. It looks like this (figures from the Lozano et al. paper:


Figure 1 [All captions from figures] Demonstration of how marks were likely made on the incisors and canines. A right‐hander pulls down with a stone tool, cutting through the object held between the anterior teeth. Occasionally, when the tool accidentally strikes the tooth’s surface, it leaves a permanent striation on the labial tooth face. Repetitive marking of the labial face allows for the assessment of which hand was used in this bimanual task
Sometimes you’ll hit your teeth with the cutting tool, and the striations (scratches) that this leaves on your teeth—in particular the incisors and canines, but especially the upper incisors—tell you what hand is doing the cutting. Try it!  Imagine you’re holding a piece of meat, or a skin, in your teeth and cutting it with your right hand (if you’re right handed, that’s what you’ll be doing). If you hit your teeth with the cutter (a sharpened stone), it will make a scratch from lower right to upper left, because the tool  will be oriented that way (hold a piece of paper in your mouth and pretend you’re cutting it). If you’re using your left hand, the cuts will be from lower left to upper right. And since you know where in the jaw the teeth are, you can determine handedness if there’s a consistent direction to the scratch marks.

Sometimes the marks will be horizontal or vertical, and sometimes they’ll be made not by humans but by taphonomic (preservation) forces, like sand scratches. You can deal with the latter by using marks only on the front edge, comparing them to those on the rear of the tooth, which should be subject to the same taphonomic modification. Also, you want not he percentage of teeth that show handedness, you want the percentage of individuals that show handedness. To deal with the first and last problem, the authors used these methods:

Thus, striations were separated into four orientation categories: horizontal (H: 0°–22.5°, 157.5°–180°), vertical (V: 67.5°–112.5°), right oblique (RO: >22.5°–<67.5°), and left oblique (LO: >112.5°–<157.5°). This underestimates the number of right or left handers; for example, an oblique mark of 21° would be classified as horizontal, so if the intervals were expanded the tooth being examined would have come from a right‐hander. However, since most studies have not published the raw data and have used the Bermúdez de Castro et al. intervals, we also used them.

Many of the teeth are isolated, especially in the Krapina sample. For this site we used Wolpoff’s reassembled tooth sets, each of which he labeled as a Krapina Dental Person (KDP). His tooth associations were based on similar morphology, occlusal wear, and interlocking interproximal facets, not on the presence of labial scratches. It is unlikely that any of the KDPs in our sample can be grouped together into a smaller number of individuals.

They also tested the “direction” hypothesis by making mouth guards that could be scratched, but also by looking at mouth guards with embedded teeth, as well looking at present day hunter-gatherers and Inuits. These showed directional striations consistent with observed handedness.

Finally, the authors analyzed several samples of hominin teeth: the total sample included five different types of humans (Homo habilis [OH 65, 1.8 million years old], Homo antecessor [from Gran Dolina, 860‐936 kya] the Sima de los Huesos fossils [430,000 years old probably ancestors of Neanderthals], European Neandertals, and modern Homo sapiens).

Here’s the earliest one, the OH-65 Homo habilis, 1.8 million years old. The graph below gives the directions of the scratches, and the predominance of the red bar (right oblique) over the blue bar (left oblique) shows that this individual was probably right handed:

OH‐65 shows a concentration of striations on the labial faces of the anterior teeth. These are visible to the naked eye. Microscopically, they conform to the striations found in much later hominids. The striations are mainly confined to the left and right I1s, the right I2, and right C1. Right oblique scratches predominate, leading to the identification of OH‐65 as a right‐hander. (n = number of striations per category) [Color figure can be viewed at]
The Gran Dolina H. antecessor individual didn’t have enough scratches to be identified but here’s the tooth of a right-hander from about 400,000 years ago (the Sima de los Huesos site):

Here are three Neanderthal teeth with the striations emphasized: the first is a left-hander and the other two right-handers based on the numerical predominance of directionally oblique scratches:

Here’s the final table that tabulates handedness. The earliest hominin was right handed, as were all 15 of the Sima de los Huesos individuals, suggested that by at least half a million years ago, right-handedness predominanted in hominins. The Neanderthals are the ones from Krapina down, and they show a 90% frequency of right-handedness, similar to humans today.

I should add that they also found directional scratches over old directional scratches (the enamel partly heals itself), so the directionality continued throughout the life of an individual, and they find directionality in teeth estimated to be from 10-year-old children as well. Since they didn’t have knives, I suspect much of this involved cutting meat, but also animal skins.

It looks as if since the hominin lineage branched from the lineage leading to chimps and bonobos, we’ve been largely right-handed: about 90%. It would be nice to have earlier fossil data, but this is pretty damn good.  I think the methodology, with its controls and observations of modern humans, is sound. The authors conclude:

We contend that the handedness data reviewed here shows that right‐handedness extends deep into the past of our species. The modern right‐handedness frequencies in earlier European human fossils from Sima de les Huesos and new specimens from the Early Pleistocene of China and Africa suggest that handedness stretches back well before the appearance of Homo sapiens. European Neandertals represent the biggest samples and continue this pattern, showing a right‐to‐left hand ratio identical to that among living Homo sapiens. In our view, the unique 9:1 ratio of right to left handers appears well before the emergence of modern Homo sapiens and is typical of our genus wherever and whenever it is found.

One question remains:

Why does there have to be a dominant hand? Why can’t humans (or those animals that show handedness) be equally dextrous with both hands?

This may be a byproduct of our brain structure (the authors posit that it’s a result of brain lateralization for language or other reasons), or there may be some other reason we don’t understand why one hand must predominate (and it can’t be random because most of us are righties, and there’s a genetic component to that). Who knows? But we do know that most of our ancestors were right-handed—at least according to these data and the data from the Fiore et al. paper.


Lozano, M. et al. 2017. Right-handed fossil humans. Evol. Anthropol. 26: 313-324.

Fiore, I., L. Bondoli, J. Radovčić, and D. W. Frayer. 2015. Handedness in the Krapina Neandertals: A Re-Evaluation. PaleoAnthropology 2015:19-36.