Yesterday The Leakey Foundation and Jeremy "Jerry" DeSilva put on a special Darwin Day event focused on Darwin's book Descent of Man, these 150 years after its initial publication. There are several short talks and some rich Q&A discussions in between them, featuring some of the authors of chapters in Jerry's edited volume A Most Interesting Problem: What Darwin's Descent of Man Got Right and Wrong about Human Evolution. If you are at all interested in human evolution or Darwin, it is probably worth your time.
The Leakey folks recorded it and posted it here on youtube: https://www.youtube.com/watch?v=KqbZD4Vmwjc
I've pasted the script to my 10 minute spiel, about halfway through the event, below.
I self-plagiarized from my chapter in A Most Interesting Problem, from the talk I've recently been giving wherever they'll have me (about sex differences in the skeleton), and from my book manuscript (I AM EVOLUTION)....
Start here...
Until we wrote this book with Jerry, I just saw Descent of Man as the source for Darwin’s formulation of sexual selection, using powerful evidence from across the animal kingdom. What I hadn’t done, until I wrote my chapter, was pay much attention to Darwin’s ideas about humans. I had only peeked at a few of those pages, had seen the word “savages,” and then couldn’t bear to actually pay attention.
What for? Being based on such outdated and limited evidence, those pages wouldn’t advance my understanding of human evolution, so I didn’t think they were worth my time. But to write this chapter, I had to give those pages my time, and while I read and re-read and raged, I realized what I already knew but hadn’t yet faced: Descent of Man’s greatest legacy is not the scientific power of sexual selection; it’s Darwin’s racist and sexist narratives of human evolution.
Descent of Man is just the absolute pits for so many people, like me. His book was better for birds, beagles, and baboons than it was for billions of humans!
So,
for scientists, Descent of Man is a foundational theoretical
masterpiece, albeit riddled with errors that Darwin can be forgiven for making
in his time, without these 150 years of scientific progress that we enjoy
today. But for humanity, Darwin’s book has been a curse.
The scientific value of Descent of Man is impossible to untangle from the oppression that it inspired.
**
Darwin’s scientific contributions in
Chapters 19 and 20 of Descent of Man look
like Victorian Age-appropriate explanations for sex differences in visible
traits in peoples across the globe—like, for how our naked, colorful skin
developed out of our ape ancestry. Because around the world, men tend to be
darker-skinned than women, Darwin proposed that variation in human skin color around
the world evolved due to sexual selection via local beauty standards.
But that people with deep ancestry in
the tropical regions of the planet have some of the most pigmented skin, is
best explained by natural selection, not sexual selection. This adaptation
likely materialized as our hominin ancestors lost a significant amount of their
protective fur covering. In its place, a melanin-rich epidermis shields the
body from the sun’s harmful UV rays, particularly at the Equator.
At high latitudes, natural selection is
also the dominant explanation for human skin color. Our bodies require UV
radiation to synthesize Vitamin D, so permitting some UV radiation into the
skin is beneficial. Both skin color extremes have strong adaptive
explanations. In between UV extremes, that clinal or spectral continuous
variation, from highly pigmented to depigmented skin, is maintained by gene
flow connecting the populations and by selection for intermediate UV levels in
between. [That last phrase in the previous is nonsense and I correct it on the fly in the video.] The evidence for this explanation for the evolution of skin color
variation around the world outweighs the evidence for Darwin’s hypothesis of
sexual selection via different beauty standards.
**
One of the strongest testaments to Darwin’s influence is that the mere existence of sex differences is enough to assume that sexual selection brought them about. Take, for example, sex differences in human height, where in all populations, men are on average taller than women.
Darwin drew inspiration from the size and strength of male, or silverback, gorillas, and scientists in his wake have helped to build the case, which is now canon, that sexual selection explains sex differences in body size. Big males won greater mating opportunities by physically dominating competitors and mates, and by females preferring to mate with these big winners, so the thinking goes.
But sex differences in human height are
at least as much about the evolutionary importance of estrogen. Estrogen is a
major driver of long bone growth in all humans and it’s biphasic, so at even
higher levels, estrogen ends long bone growth with the fusion of the growth
plates. When estrogen peaks, teenage girls stop gaining stature. This estrogen
peak at puberty is fundamental to ovarian development and the initiation of
regular menstrual cycling. Boys, who are growing in step with girls until
puberty, stop gaining stature just a few years after girls do, because there is
nothing to stop them earlier; higher estrogen would be incompatible with male
reproductive development and function. Eventually young men have enough
estrogen in their more senescent skeletal system to also stop growing.
There are no male or female genes for height and there are no male or female bones; there is only common biology of skeletal growth shared among humans, where similar processes significantly controlled by estrogen play out differently in different bodies during development. As of now, sex differences in the duration of long bone growth are a byproduct of the way that the human reproductive system evolved to function, thanks in large part to estrogen. Still, sexual selection for tall men dominates the evolutionary story. It sure is a compelling one.
Perhaps
more than any other science, evolutionary science is a collection of stories,
or fictions, about facts. For example, FACT men are on average taller than
women FICTION because of their big winning male forebears. Fictions are
supposed to be difficult to establish as fact in science, and they’re far too
easy to establish as fact in the zeitgeist. If we are better aware of the
precarity of our fictions… if we improve the scientific explanations of visible
sex differences, like height, then that science will be less likely to inspire
unscientific beliefs about invisible, imagined sex differences. Fewer minds will
leap illogically from ‘men are taller’ to ‘men obviously evolved for
competition and dominance’ as if women did not.
**
Underneath Descent of Man’s ambitious
scientific contribution to human evolution lies much more than surface beauty.
This is Darwin begetting every caveman-inspired nugget of dating advice and
every appeal to innate gender roles at home, in the workplace, in science and
tech, and on Wallstreet. This is where Darwin first turned his concept of
sexual selection loose on humans, launching the evolutionary narrative that
dominates pop culture starring QUOTE “the strongest and boldest men… in
contests for wives”.
In Descent
of Man, Darwin parlayed visible anatomical differences between sexes—like
those in skin color and height—into the evolutionary logic behind why Man and
Wife perform differently, in matters of love, sex, parenting, cognitive feats, comedy,
and seemingly everything else, according to the contemporary world views he
continues to shape.
But, pop culture has been slow to adopt new knowledge that has complicated and overturned old facts. Much of the novel insights on human evolution, including especially the evolution of human skin color variation, these have come from women, despite persistent beliefs like Darwin’s that, QUOTE “Man is more courageous, pugnacious and energetic than woman, and has a more inventive genius.” Darwin even concludes, as if by scientific logic, that, QUOTE “man has ultimately become superior to woman.” For Darwin, women were wives but men were so much more than husbands, this seeded his science of sex differences. From his view of life, Darwin penned nature’s seal of approval.
Darwin
naturalized gender differences, made them biological, made them adaptive, made
them morally valuable. All of us suffer from bias, but powerful men seem to
share one particular form of bias when it comes to our species’ shared origin
story—fuhrers and ex-presidents… their oppressive human evolutionary narratives
sound a lot like Darwin’s, which directly inspired the exclusion of women from
higher education and from science. Today, there is an increasing understanding that beliefs in gender
essentialism, in natural rigid gender stereotypes of masculinity and femininity,
like boys are active and dominant and girls are sexual and
maternal, these beliefs are correlated to poor educational outcomes in boys
and girls and to sexual assaults by boys and men.
Getting humanity’s origin story right matters a great deal to humanity.
**
The stories we tell about the facts of
evolution are in dire need of diversity. The way to get there is not merely to
be more correct or less biased than Darwin, it is not merely to be the best
version of ourselves, it is to be proactively bigger than any one person can
possibly be and… to be proactively bigger than even science can be. We do not need science to demonstrate that women
and people of color are not inferior… to demonstrate that we are
not less evolved, less brilliant and inventive, less deserving of opportunity, power,
influence, admiration, and freedom* than white men.
While many scientists and scholars have met Darwin’s bias and prejudice with science, science is not the only, or even a necessary way to demonstrate humanity. That is partially because science does not yet represent humanity. Science will continue to write a better story of human origins and evolution, but if science were all it takes, then we would have that better story by now. Science is not the sole or even primary author of humanity’s shared origin story, humanity is.
Let’s write a great story together. Let’s write one that’s worthy of the entire species, a story that everyone can embrace.
*I'm not positive but I think that my use of "freedom" inspired a discussion in the live chat about Darwin and his family being abolitionists. Yes, they were. But my use of freedom here refers to something other than the abolition of slavery. I'm referring to the freedom that more wealthy white men enjoy than anyone else. Who wants to live in a world where freedom is merely the absence of slavery!? Freedom is attained by the things I listed before it and so much more...
