Richard Leakey dies at 77

January 2, 2022 • 12:22 pm

This just in: Richard Leakey, well known paleoanthropologist, conservationist, and politician, has died at 77.  (Two of his team’s finds are H. rudolfensis and “Turkana Boy,” placed in H. ergaster.) A brief bio from the France 24 website:

World-renowned Kenyan conservationist and politician Richard Leakey, who unearthed evidence that helped to prove humankind evolved in Africa, died on Sunday at the age of 77, the country’s president said.

“I have this afternoon… received with deep sorrow the sad news of the passing away of Dr Richard Erskine Frere Leakey, Kenya‘s former Head of Public Service,” said Kenyan President Uhuru Kenyatta in a statement late Sunday.

Leakey, the middle son of famed paleoanthropologists Louis and Mary Leakey, had no formal archaeological training of his own but led expeditions in the 1970s that made groundbreaking discoveries of early hominid fossils.

His most famous find came in 1984 with the uncovering of an extraordinary, near-complete Homo erectus skeleton during one of his digs in 1984, which was nicknamed Turkana Boy.

In 1989, Leakey was tapped by then President Daniel arap Moi to lead the national Kenya Wildlife Service (KWS), where he spearheaded a vigorous campaign to stamp out rampant poaching for elephant ivory.

In 1993, his small Cessna plane crashed in the Rift Valley. He survived but lost both legs.

He also tried his hand at politics, ran civil society institutions, and briefly headed Kenya’s civil service.

In 2015, despite ailing health, he returned to the helm of the KWS for a three year term at the request of Kenyatta.

Here’s Leakey in 2010:

And Turkana boy (1.5-1.6 million years old), the most complete early hominin skeleton found to date:

A nice lecture from Matthew on genetics and human evolution

October 15, 2021 • 12:45 pm

Here’s a virtual lecture on genetics and evolution that Matthew gave the other day to the Cardiff University’s School of Medicine. It was intended for the general public, was just posted on YouTube, and I’ve listened to it.  I have been most enlightened, and unless you already know this stuff you will be, too—it’s an up-to-date explication of what we know about the evolution of the genus Homo and what genetics tells us about our post. Of course, this field changes rapidly, and more surprises are in store. And mysteries remain about what we do know: why, for example, did the Neanderthals disappear?

At the end, Matthew considers the question, “What does it meant to be human?” and reprises the lessons and implications of recent genetic studies of anthropology. You can see how Matthew’s knowledge of the topic and his enthusiasm for conveying it has made him a popular lecturer, and garnered him teaching awards.

The formal lecture ends at 54:00, and then Matthew answers the viewers’ questions.

Fire use by hominins: an example of rapid cultural evolution?

July 26, 2021 • 9:15 am

Yesterday we discussed the possibility of cultural evolution (dissemination of a behavior or skill through imitation and learning) in cockatoos, which attracted a lot of attention, probably because of its parallel with human cultural evolution. (The cockatoos seem to have learned to open garbage bins by watching each other.) And in our species there are a gazillion examples, especially since transportation allowed innovations to be spread quickly and widely. You can think of lots of cases: blue jeans, cuisines from other places, music, and, earlier than that, printing, the wheel (some cultures never got it) and even religion.

The new paper in Proc. Nat. Acad. Sci. below, however, suggests what may have been the very first behavior that spread though species of Homo (not only H. sapiens, but perhaps Neanderthals, which some consider a different species) through movement of individuals: the use of fire.  Click on the screenshot to read the article (free) below, or get the pdf here. The reference is at the bottom.

Fire, of course, has many uses: besides cooking meat and tubers, it can be used to harden wood to make spear points, change the quality of stone to make it easier to flake, and to keep yourself warm. Other uses are given in the Wikipedia article “Control of fire by early humans.”

The MacDonald et al. paper collects evidence of fire use from species of Homo, concluding that it got started about 400,000 to 350,000 years ago and then spread rapidly throughout the species. The rapidity of spread then led them to propose what kind of social structure was present in humans at that time.  This contradicts speculations H. erectus controlled the use of fire about 1.5 million years ago; the authors find that evidence unconvincing.

The problem is to distinguish anthropogenic (“human caused”) fire from natural wildfires. But there are ways of doing this, as the article summarizes. Hearths and charred animal bones are one way. Here’s another bit of evidence: a fire-hardened wooden spear from, coincidentally, about 380,000-400,000 years old, part of a group of artifacts found in Germany:

I can’t evaluate the quality of the evidence, but the authors summarize a lot of data to conclude that regular fire use began about 400,000 years ago, and spread quickly throughout the Old World, with evidence coming from Portugal, Spain, France, Israel, and Morocco. Two quotes:

. . . a review by Roebroeks and Villa identified a clear pattern for Europe: there the record strongly suggests that anthropogenic fire use was very rare to nonexistent during the first half of the Middle Pleistocene, as exemplified by the absence—bar a few dispersed charcoal particles—of fire proxies in deeply stratified archaeological karstic sequences, such as the Atapuerca site complex in Spain or the Caune de l’Arago at Tautavel (France), as well as from such prolific open-air sites as Boxgrove in the United Kingdom. In contrast, the record from 400 ka onward is characterized by an increasing number of sites with multiple fire proxies (e.g., charcoal, heated lithics, charred bone, heat-altered sediments) within a primary archaeological context.

. . . The spatiotemporal pattern of the appearance in the archaeological record of an innovation provides evidence relevant for identifying how the innovation came to be widely distributed: that is, through independent innovation, demic processes, cultural diffusion, or genetic processes. The fact that regular fire use appeared relatively quickly across the Old World and in different hominin subpopulations strongly suggests that the behavior diffused or spread from a point of origin rather than that it was repeatedly and independently invented.

Since fire appeared in both warm and cold places around the same time, the authors suggest that its inception was not correlated with “environmental pressures” (e.g., cold). And because the spread was so rapid, the authors claim, correctly, that the spread throughout the Old World was very unlikely to have been caused by the diffusion of genes producing the tendency to create fire, which would spread only very slowly. Likewise, the near-simultaneity makes it seems unlikely that the use of fire was invented independently by several groups.

If fire use did spread through imitation and learning, then, what does that say about the social structure of early humans? If we were divided up into groups of xenophobic hunter-gatherers who didn’t interact, that would not facilitate the spread of fire. Why would a group give the skill to a competitor group? There are two alternatives.

The first, “demic diffusion,” is that a “deme” (a cohesive populations of hominins) spread rapidly, taking with it the fire use they invented. This seems unlikely given that the spread was more rapid than one could imagine a single population could migrate.

The alternative comprises groups that tolerated each other, and were at least somewhat friendly. As the authors suggest, there was a more “fluid social structure with multiple levels of clustering in social networks”. In other words, perhaps hominims were more interactive than we thought.

Well, we have no direct evidence for that, and it would be hard to come by. And I’ll let other physical anthropologists judge the “simultaneous spread” hypothesis. But I wanted to bring this up because the scenario is at least plausible, and it may be the first evidence for cultural evolution in our genus.

There’s one other trait they add in to the mix as another behavior that spread by cultural evolution: the “Levallois technology” for knapping stone (striking flakes off a stone like flint to make weapons and other implements). This, say the authors, can be learned only through “close and prolonged observation combined with active instruction.” Here’s the Levallois method, which involves producing a flint core in such a way that sharp flakes, useful for tools, can be easily struck off:

The authors posit that this technology also originated in one place, but about 100,000 years later than fire (and surely in a different place), and then spread rapidly among groups in a similar way: non-hostile group interactions in a multi-level social network.

I’ll close with the authors’ final paragraph, summarizing their views:

We hypothesize that around 400 ka, cultural processes supported change in technology across wide areas. This indicates, at a minimum, a degree of social tolerance for individuals from different groups, and suggests the less minimal but still plausible hypothesis that more intensive cooperative interactions within larger-scale networks were already in place, occasionally crossing the boundaries between what we usually infer to have been different biological populations within the wider hominin metapopulation. [JAC: I think they’re referring to movement between “modern H. sapiens and Neanderthals. After all, these groups did mate with each other] We conclude that the spatial and temporal pattern of the appearance of regular Middle Pleistocene fire use documented in the archaeological record signals more than the advent of an important tool in the hominin toolbox: the presence of cultural behavior more like that of humans today than of our great ape relatives. We suggest that long before the cultural florescence associated with the late MSA/Middle Pleistocene and to a greater extent LSA/Upper Paleolithic periods, hominins were beginning to develop the capacities for complexity, variability, and widespread diffusion of technology and behavior that we tend to associate only with H. sapiens.


MacDonald, K., F. Scherjon, E. van Veen, K. Vaesen, and W. Roebroeks. 2021. Middle Pleistocene fire use: The first signal of widespread cultural diffusion in human evolution. Proceedings of the National Academy of Sciences 118:e2101108118.

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.

Today’s readings

February 13, 2021 • 1:15 pm

Here are a couple of readings for your weekend delectation. Click on the screenshots to read them. I’ve quoted an excerpt from each, and Sullivan’s piece may be paywalled:

In The Guardian, Adam Rutherford asks us to see Darwin as a man of his time, complex and imperfect by today’s moral lights, but not to be erased or cast aside. I’ve written much of what’s in this column before, but it’s good to see Adam agree.

No one sensible is calling for the cancelling of Darwin, though that does not mean that he and his work are exempt from historical reassessment. His descriptions of differences between the sexes and various human populations are well documented and studied, and some of it now makes for uncomfortable reading. He was right about some of the most important ideas anyone ever had, and wrong about others. Unlike the work of Galton, his ideas did not generate policy implications, which, at least in Galton’s case, were enacted around the world for much of the 20th century with genocidal consequences. These distinctions require discussion, scholarship, context and nuance, and above all, they should be intellectually honest.

Who knows what we will be scalded for in 150 years’ time. This is the process of history. Modern debates framed along the spurious lines that we cannot change history, and therefore should cast our statues in aspic, fail to understand that history, by definition, is always changing. It is the past, not history, that is fixed, and the job of historians is to constantly reassess it with new discoveries and new analysis in our current culture.

This is ultimately why The Descent of Man is my favourite Darwin book, because even the greatest of us are merely people – complex and flawed. It is a deeply humanist book. Darwin casts aside the idea that “savage races” are distinct from the civilised, while using language that bears the indelible stamp of imperial dominance. Yet at the same time, he sees that humankind’s strength lies in cooperation, liberalism and kindness. . .

From John McWhorter’s Substack column; “It Bears Mentioning” (free, but you should subscribe):

McWhorter attacks several tropes implying that structural racism is alive, well, and operating today. A sample, with the tropes in italics:

The role of Black labor in building the Southern economic infrastructure has been routinely denied.

Okay, has been – but the use of the perfect here is subtle. Elvis has left the building – it implies that his leaving rings with import here in the present, unlike Elvis left the building. Just who, today, is denying black people’s role here? Which professionals? Which people anyone listens to? Or, if the denial was common coin in the past – which it was – then precisely what do we do with that in the today in which we live?

The contributions that Black scholars have made in the humanities, the life sciences and the natural sciences have been lost because of segregated workplaces.

Have been – okay. But which contributions of this kind are being “lost” today, anymore than, of course, those “lost” by pretty much all scholars, since none but a sliver of scholarship ever really sees the light of day? Would a trawl of the books covered by The New York TimesThe Washington PostThe Atlantic and The New Yorker actually reveal a downplaying of important black work?

The work of Black creative artists has been disregarded since it became appropriated into the national cultural apparatus.

Can we really say this especially of America since last spring, when so very much welcome attention has been paid to black art of all kinds? Does the current situation really justify this acrid judgment?

Note that in certain circles, my very posing of these questions – just asking questions – is considered deeply obnoxious, arrogant, inappropriate. That feeling is so deep-seated that you can forget that it isn’t normal.

From Andrew Sullivan’s The Weekly Dish. The title speaks for itself:

. . . the violence was real and, in several cases, fatal. And no clownishness should distract us from the gravity of the event, or who was responsible for it. For four years, we had a president who expressed contempt for democratic procedures; who had long viewed every US election as rigged; who refused in 2016 and 2020 to respect the results in advance; who claimed millions of illegal aliens had voted for his opponent in 2016; who attempted to stop the counting of votes after election night; who tried to lean on state officials and legislators to reverse certification; who falsely claimed, without any credible evidence, that he had won in a landslide; who wouldn’t attend his successor’s inauguration; and who has refused even now to concede he lost at all.

There has never been a president who has done any of this: express contempt for the democracy he leads, refuse to accept the legitimate results of an election, and attempt to stay in power by marshaling violence in the streets. There are no parallels among any first-world modern democracies for this kind of behavior by a head of state or prime minister. No Western leader, after losing an election, has ever insisted he actually won it in a landslide — and refused to grant any legitimacy to his successor. It is such a grotesque violation of a president’s oath of office that, only a few years ago, it would have been deemed an impossibly far-fetched scenario.

Impeaching and convicting a president for this is therefore a no-brainer. It is the bare minimum we need to do to restore democratic stability. That any Senator is even considering acquitting Trump is a scandal, a sign that one major party has abandoned even the most basic rules of democratic life. That so many “constitutional” Republicans, like Mike Lee of Utah or Rand Paul of Kentucky, have managed to find some arcane way to justify this excrescent assault on our democracy reveals their moral depravity and intellectual incoherence. That so many ordinary Republicans can justify this in any way — and still insist that the election was stolen — is a sign that one party in our system has effectively ceased to be a democratic one at all.

From Wilfred Reilly, a black man, at Spiked. Stuff like this will undoubtedly get him labeled a “self-hating black”. Here he talks about several gaps between blacks and whites—inequities—that are universally ascribed to present racism. Reilly disagrees:

Thirty years ago, economist June O’Neill unpacked a well-known ratio of 82:100 for the earnings of black vs white men. Less technically put, black guys made about 80 cents for each dollar that white guys earned. This gap was – then as now – almost universally attributed to racism. But O’Neill pointed out that simply adjusting for variables like median age, where someone lives and years of education closed the gap substantially.

The most common age for a black person in the US is 27, while the most common age for a white person is 58, and blacks are far more likely than whites to live in the south – where wages are lower for everyone.

Adding tested IQ to the equation closed the ratio to 95.5:100, and adjusting for years of work experience (which is closely related to age) closed it to 99.1:100. O’Neill followed up this research in 2005, finding similar results. Controversial as it sounds in our hyper-politicised society, people of different races with the same qualifications succeed to roughly the same degree today. While few would deny that proportionately more black Americans are poor today because of past conflict and oppression, the effect of contemporary racism seems to be in the order of a few percentage points.

Note that he’s talking about contemporary racism, not past racism, whose reality he readily admits. But the solutions to past versus present racist practices may be very different.

And some archaeology. I didn’t know any of this, but geologists have long known that the stones of Stonehengs were quarried in Wales—a long way away. Now there’s increasing evidence, recounted in this article, that the big stones of Stonehenge were actually erected in a similar circular structure in Wales, and the dragged 175 miles (they didn’t have wheels).

You can read the original paper in the journal Antiquityand it all fits: stone positions, dates, and the same “function” of showing the solstice. Here’s the remnants of the original circle in Wales (I’ve put an arrow by the original circle, just recently undearthed).

As one archaeologist says about The Big Drag from Wales to the present site:

[Dr. Parker Pearson] favors a land route, over which the massive stones, each weighing up to four tons, could be hauled on rows of poles and wooden sledges by as many as 400 people. “This would have been like going to the moon,” he said, “but the Neolithic equivalent.”

World’s oldest representational art: an Indonesian warty pig from 45,000 years ago

January 23, 2021 • 1:45 pm

Here from Science Advances via National Geographic, is the painting of a wild pig from the Indonesian island of Sulawesi. AT 45,000 years old, it’s world’s oldest cave art, and in fact the oldest known representational art of any sort.


Here’s the paper reporting it (click on screenshot), and a free pdf is here:

The very oldest art comes not from Europe or Africa, but from Indonesia; but surely there was much earlier representational art. The subject is presumably a Celebes warty pig (Sus celebensis), a species still with us, and the artist presumably an anatomically modern human (H. sapiens sapiens).

Here’s the subject. Not a bad representation, eh?

From Wild Pig, Peccary & Hippo Specialist Groups.

And a few words from the authors (“AMH” means “anatomically modern humans”)

On the basis of the presently available evidence, we are unable to definitively conclude that the dated figurative rock art depiction from Leang Tedongnge is the handiwork of cognitively “modern” members of our species. However, this seems to be the most likely explanation given the sophistication of this early representational artwork and the fact that figurative depiction has so far only been attributed to AMH everywhere else in the world.

If so, the dated pig image from Leang Tedongnge would appear to provide some of the earliest evidence, if not the earliest, for the presence of our species in Wallacea. The minimum age of this artwork is compatible with the earliest established indications of AMH from excavated deposits in the Lesser Sunda islands, which formerly provided the oldest archaeological evidence for H. sapiens in Wallacea (~44.6 ka cal BP). Hence, dating results for the Leang Tedongnge painting underline the view that representational art, including figurative animal art and depictions of narrative scenes, was a key part of the cultural repertoire of the first AMH populations to cross from Sunda into Wallacea—the gateway to the continent of Australia.

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).

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.


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.



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 ( 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.