There’s a story that many scientists tell about the evolution of human skin color.
The story goes roughly like this:
In the beginning, our ancestors had dark fur and lightly pigmented skin. This was perhaps six million years ago? Over time, our ancestors lost their fur and needed darkly pigmented skin to protect themselves from the harsh light of the sun.
Later, some people left their ancestral homeland. Migratory humans covered the globe. As humans traveled farther from the equator, they evolved light skin again – otherwise they’d have too little vitamin D.
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In Joanne Cole (author) & Bruce Degen (illustrator)’s The Magic School Bus Explores Human Evolution (which is surprisingly good! You can read my review here), this story is told in a single panel.
Variants on this story percolated through the scientific literature for years, but the version above is derived largely from the work of anthropologists Nina Jablonski & George Chaplin. In their article “The Evolution of Skin Coloration,” they write that “As hominins migrated outside of the tropics, varying degrees of depigmentation evolved to permit ultraviolet-light-induced synthesis of vitamin D.”
This story is often treated as accepted science, even by researchers who describe human evolution from an explicitly anti-racist perspective. For example, in A Brief History of Everyone Who Ever Lived, Adam Rutherford writes that “The unglamorous truth is that there are but a handful of uniquely human traits that we have clearly demonstrated are adaptations evolved to thrive in specific geographical regions. Skin color is one. The ability to digest milk is another, which fits perfectly with the emergence of dairy farming.”
However, this story about the evolution of human skin color isn’t supported by the actual data. Instead, it’s based on Eurocentric misconceptions about what sort of environment and lifestyle are “normal” for human beings.
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Unquestionably, darkly pigmented skin can protect humans from sunlight. And sunlight is dangerous! You should wear sunscreen. (I’m sure that somebody has told you this already.)
But the benefits of light skin have been vastly overstated by (light-skinned) researchers. And a quick glance at the data is enough to demonstrate the major flaws in the evolutionary story I described above.
That same page of The Magic School Bus Explores Human Evolution includes a world map with a (again, surprisingly accurate!) depiction of the paths that ancient humans took to populate the planet.
Looking at those red arrows, you’ll see several occasions when groups of humans migrated farther from the equator. The people who settled in France, Korea, and Patagonia had all reached similar latitudes. (As did the humans who settled in New Zealand, but they only arrived about 800 years ago, which probably isn’t enough time to expect dramatic shifts in skin color. Especially given the likelihood of continued gene flux across latitudes – by the time anyone reached New Zealand, people were probably traveling to and fro by boat often, rather than forming an isolated community.)
If the above story about the evolution of human skin color were correct, we’d expect that indigenous people from France, Korea, and Patagonia would all have similar skin color. Indeed, artist Gail McCormick worked closely with Jablonski & Chaplin to create a cut-paper map depicting the indigenous skin color that their story predicts for various regions.
But this map doesn’t match the skin color we actually see from humans across the globe. The indigenous people of France evolved lightly pigmented skin. The indigenous people of Korea, Patagonia, and North America did not.
Jablonski & Chaplin arrived at their conclusion because they considered very few human populations; Figure 4 from their paper, which I’ve included below, depicts in white all the regions of the globe that they left out of their data set.
Each human migration was another natural experiment: Does migration away from the equator result in lighter skin?
For the people migrating into Europe, the answer is pretty unambiguously “yes.” We have evidence of dramatic, rapid selection for genes that result in lighter skin among these people. Many of the gene variants responsible for lightly pigmented skin in Europeans had been long present among ancient humans living in Africa (as documented by Crawford & colleagues in “Loci Associated with Skin Pigmentation Identified in African Populations”), but then spread rapidly among Europeans approximately 4,000 years ago (as documented by Mathieson & colleagues in “Genome-Wide Patterns of Selection in 230 Ancient Eurasians”).
The dramatic selection for genes associated with lightly pigmented skin in Europe occurred within the span of about a thousand years, and occurred about 30,000 or 40,000 years after Homo sapiens first populated that region.
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Among the various groups of ancient humans who migrated toward similar latitudes, only the indigenous people of Northern Europe evolved lightly pigmented skin. This trait spread rapidly (by evolutionary standards) about 4,000 years ago.
This timing is similar to the spread of lactose tolerance genes among the people of Northern Europe. Most animals, including most humans, can’t digest milk in adulthood. Even among humans who live in cultures where cows’ milk is a major component of the diet, many people can’t digest it and will experience routine gastrointestinal distress and diarrhea. (Which is serious! Although a few bottles of Gatorade would save their lives, diarrhea still kills about 2 million people per year. Among ancient humans, diarrhea could easily cause deaths by malnutrition, dehydration, or increased susceptibility to disease.)
And yet, just before the Europeans’ vast spree of kidnapping, abduction, and resource extraction led to massive amounts of human migration (which began approximately 500 years ago), nearly 95% of the people living in Europe had the genes for lactose tolerance.
That’s a huge change, and really fast! Which should make us realize that something strange might be going on with this group of people – they must’ve had particularly atrocious diets. Which helps explain why they’d need lighter skin.
After all, vitamin D is a dietary nutrient. If you get enough vitamin D from your food, there’s no downside to darkly pigmented skin. And, as David Graeber & David Wengrow describe comically in The Dawn of Everything(“We might call this the ‘all the bad spots are taken!’ argument”), most ancient humans chose to live in places where they could find food, water, and shelter. Otherwise they’d migrate.
Yet, in a savage twist of fate, the same culture that generally resulted in low-quality diets – farming – also made migration more difficult. People stayed near their farms, with their insufficient amounts of low-quality food, because that way they’d at least have something.
I’ve written previously about the social and environmental repercussions of ancient farming – a lovely essay, in my opinion! – but in order to understand the evolution of skin color, all we really need to know is the impact of farming on human health. As James Scott writes in Against the Grain,
“Evidence for the relative restriction and impoverishment of early farmers’ diets comes largely from comparisons of skeletal remains of farmers with those of hunter-gatherers living nearby at the same time. The hunter-gatherers were several inches taller on average. This presumably reflected their more varied and abundant diet. It would be hard, as we have explained, to exaggerate that variety. Not only might it span several food webs – marine, wetland, forest, savanna, arid – each with its seasonal variation, but even when it came to plant foods, the diversity was, by agricultural standards, staggering. The archaeological site of Abu Hureyra, for example, in its hunter-gatherer phase, yielded remains from 192 different plants, of which 142 could be identified, and of which 118 are known to be consumed by contemporary hunter-gatherers.”
The crops and livestock raised by farmers in Northern Europe provide very little vitamin D. But ancient humans often settled in areas where they could catch fish, which provides plenty of dietary vitamin D (as measured by Schmid & colleagues for their study “Natural Vitamin D Content in Animal Products”).
As it happens, if the picture from The Magic School Bus Explores Human Evolution were an accurate depiction of those people’s diet (not to mention their clothes, exposing quite a bit of skin!), they’d probably experience very little selective pressure for lighter skin.
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Whenever we discuss evolution, it’s important to remember that natural selection doesn’t enrich for traits that are “better.” There’s rarely any such thing as “better.” Consider: the ancestors of starfish had brains! But – given their particular environment – their lineage was more successful after evolving to be brainless. Or: the ancestors of penguins could fly! But – given their particular environment – their lineage was more successful after evolving to be flightless.
We humans have long legs and arched feet that are great for running, but these same long legs and stubby toes make us so much worse at climbing trees than a chimpanzee. It’s a trade-off. (And a trade-off that I’m pretty happy with, given that I love to run and am afraid of heights.)
Lightly pigmented skin carries a very clear cost – UV penetration with its attendant folate degradation, skin cancers, and discomfort – and only carries a compensatory benefit at extreme northern or southern latitudes among ancestral populations with diets low in vitamin D.
We do ourselves a major disservice – and perpetuate Eurocentric racism – if we consider the selective pressures encountered by one particular group of Homo sapiens to be the default against which all others are measured.
Recently my spouse & I reviewed Jennifer Raff’s Origin: A Genetic History of the Americas for the American Biology Teacher magazine (in brief: Raff’s book is lovely, you should read it! I’ll include a link to our review once it’s published!), which deftly balances twin goals of disseminating scientific findings and honoring traditional knowledge.
By the time European immigrants reached the Americas, many of the people living here told stories suggesting that their ancestors had always inhabited these lands. This is not literally true. We have very good evidence that all human species – including Homo sapiens, Homo neaderthalensis, and Homo denisovans among possible others – first lived in Africa. Their descendants then migrated around the globe over a period of a few hundred thousand years.
As best we know, no lasting population of humans reached the Americas until about twenty thousand years ago (by which time most human species had gone extinct – only Homo sapiens remained).
During the most recent ice age, a few thousand humans lived in an isolated, Texas-sized grassland called Beringia for perhaps a few thousand years. They were cut off from other humans to the west and an entire continent to the east by glacial ice sheets. By about twenty thousand years ago, though, some members of this group ventured south by boat and established new homes along the shoreline.
By about ten thousand years ago, and perhaps earlier, descendants of these travelers reached the southern tip of South America, the eastern seaboard of North America, and everywhere between. This spread was likely quite rapid (from the perspective of an evolutionary biologist) based on the diversity of local languages that had developed by the time Europeans arrived, about five hundred years ago.
So, by the time Europeans arrived, some groups of people had probably been living in place for nearly 10,000 years. This is not “always” from a scientific perspective, which judges our planet to be over 4,000,000,000 years old. But this is “always” when in conversation with an immigrant who believes the planet to be about 4,000 years old. Compared with Isaac Newton’s interpretation of Genesis, the First People had been living here long before God created Adam and Eve.
If “In the beginning …” marks the beginning of time, then, yes, their people had always lived here.
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I found myself reflecting on the balance between scientific & traditional knowledge while reading Gabriel Andrade’s essay, “How ‘Indigenous Ways of Knowing’ Works in Venezuela.” Andrade describes his interactions with students who hold the traditional belief in partible paternity: that semen is the stuff of life from which human babies are formed, and so every cis-man who ejaculates during penetrative sex with a pregnant person becomes a father to the child.
I appreciate partible paternity because, although this belief is often framed in misogynistic language – inaccurately grandiose claims about the role of semen in fetal development, often while ignoring the huge contribution of a pregnant person’s body – the belief makes the world better. People who are or might become pregnant are given more freedom. Other parents, typically men, are encouraged to help many children.
Replacing belief in partible paternity with a scientifically “correct” understanding of reproduction would probably make the world worse – people who might become pregnant would be permitted less freedom, and potential parents might cease to aid children whom they didn’t know to be their own genetic offspring.
Also, the traditional knowledge – belief in partible paternity – might be correct.
Obviously, there’s a question of relationships – what makes someone a parent? But I also mean something more biological — a human child actually can have three or more genetic contributors among their parents.
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Presumably you know the scientific version of human reproduction. To wit: a single sperm cell merges with a single egg cell. This egg rapidly changes to exclude all the other sperm cells surrounding it, then implants in the uterine lining. Over the next nine months, this pluripotent cell divides repeatedly to form the entire body of a child. The resulting child has exactly two parents. Every cell in the child’s body has the same 3 billion base pair long genome.
No scientist believes in this simplified version. For instance, every time a cell divides, the entire genome must be copied – each time, this process will create a few mistakes. By the time a human child is ready to be born, their cells will have divided so many times that the genome of a cell in the hand is different from the genome of a cell in the liver or in the brain.
In Unique, David Linden writes that:
Until recently, reading someone’s DNA required a goodly amount of it: you’d take a blood draw or a cheek swab and pool the DNA from many cells before loading it into the sequencing machine.
However, in recent years it has become possible to read the complete sequence of DNA, all three billion or so nucleotides, from individual cells, such as a single skin cell or neuron. With this technique in hand, Christopher Walsh and his coworkers at Boston Children’s Hopsital and Harvard Medical School isolated thirty-six individual neurons from three healthy postmortem human brains and then determined the complete genetic sequence for each of them.
This revealed that no two neurons had exactly the same DNA sequence. In fact, each neuron harbored, on average, about 1,500 single-nucleotide mutations. That’s 1,500 nucleotides out of a total of three billion in the entire genome – a very low rate, but those mutations can have important consequences. For example, one was in a gene that instructs the production of an ion channel protein that’s crucial for electrical signaling in neurons. If this mutation were present in a group of neurons, instead of just one, it could cause epilepsy.
No human has a genome: we are composite creatures.
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Most scientists do believe that all these unique individual genomes inside your cells were composed by combining genetic information from your two parents and then layering on novel mutations. But we don’t know how often this is false.
Pluripotent (“able to form many things”) cells from a developing human embryo / fetus / baby can travel throughout a pregnant person’s body. This is quite common – most people with XX chromosomes who have given birth to people with XY chromosomes will have cells with Y chromosomes in their brains. During the gestation of twins, the twins often swap cells (and therefore genomes).
At the time of birth, most humans aren’t twins, but many of us do start that way. There’s only a one in fifty chance of twin birth following a dizygotic pregnancy (the fertilization of two or more eggs cells released during a single ovulation). Usually what happens next is a merger or absorption of one set of these cells by another, resulting in a single child. When this occurs, different regions of a person’s body end up with distinct genetic lineages, but it’s difficult to identify. Before the advent of genetic sequencing, you might notice only if there was a difference in eye, skin, or hair color from one part of a person’s body to the next. Even now, you’ll only notice if you sequence full genomes from several regions of a person’s body and find that they’re distinct.
For a person to have more than two genetic contributors, there would have to be a dizygotic pregnancy in which sperm cells from unique individuals merged with the two eggs.
In the United States, where the dominant culture is such that people who are trying to get pregnant are exhorted not to mate with multiple individuals, studies conducted in the 1990s found that at least one set of every few hundred twins had separate fathers (termed “heteropaternal superfecundication”). In these cases, the children almost certainly had genomes derived from the genetic contributions of three separate people (although each individual cell in the children’s bodies would have a genome derived from only two genetic contributors).
So, we actually know that partible paternity is real. Because it’s so difficult to notice, our current estimates are probably lower bounds. If 1:400 were the rate among live twins, probably that many dizygotic pregnancies in the United States also result from three or more genetic contributors. Probably this frequency is higher in cultures that celebrate rather than castigate this practice.
Honestly, I could be persuaded that estimates ranging anywhere from 1:20 to 1:4,000 were reasonable for the frequency that individuals from these cultures have three or more genetic contributors.** We just don’t know.
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I agree with Gabriel Andrade that we’d like for medical students who grew up believing in partible paternity to benefit from our scientific understanding of genetics and inheritance – this scientific knowledge will help them help their patients. But I also believe that, even in this extreme case, the traditional knowledge should be respected. It’s not as inaccurate as we might reflexively believe!
The scientific uncertainty I’ve described above doesn’t quite match the traditional knowledge, though. A person can only receive genetic inheritance from, ahem, mating events that happen during ovulation, whereas partible paternity belief systems also treat everyone who has sex with the pregnant person over the next few months as a parent, too.
But there’s a big difference between contributing genes and being a parent. In Our Transgenic Future: Spider Goats, Genetic Modification, and the Will to Change Nature, Lisa Jean Moore discusses the many parents who have helped raise the three children she conceived through artificial insemination. Even after Moore’s romantic relationships with some of these people ended, they remained parents to her children. The parental bond, like all human relationships, is created by the relationship itself.
This should go without saying, but: foster families are families. Adopted families are families. Families are families.
Partible paternity is a belief that makes itself real.
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** A note on the math: Dizygotic fertilization appears to account for 1:10 human births, and in each of these cases there is probably at least some degree of chimerism in the resulting child. My upper estimate for the frequency that individuals have three or more genetic contributors, 1:20, would be if sperm from multiple individuals had exactly equal probabilities of fertilizing each of the two egg cells. My lower estimate of 1:4,000 would be if dizygotic fertilization from multiple individuals had the same odds as the 1:400 that fraternal twin pairs in the U.S. have distinct primary genetic contributors. Presumably a culture that actively pursues partible paternity would have a higher rate than this, but we don’t know for sure. And in any case, these are large numbers! Up to 5% of people from these cultures might actually have three or more genetic contributors, which is both biologically relevant and something that we’d be likely to overlook if we ignored the traditional Indigenous knowledge about partible paternity.
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header image from Zappy’s Technology Solution on flickr
Our criminal justice system ensnares people from all walks of life. Occasionally we’ll hear about the arrest of a wealthy sociopath with a penchant for child abuse, like Jared Fogel or Jeffrey Epstein.
But, let’s face it. Justice in this country isn’t applied fairly. If you’re wealthy, your behavior has to be a lot more egregious for you to reap the same punishments as a poor person. If you look white, your behavior has to a lot more egregious for you to reap the same punishments as a black person.
There’s abundant statistical evidence to back up these claims. But the Supreme Court won’t allow any particular individual to petition for reduced punishment based on the statistical evidence. After all, prosecutors, judges, and juries ostensibly came to their decisions based on the unique details of each individual case. Just because people who resemble you are often treated unfairly doesn’t mean that you were treated unfairly, too.
Because we apply punishment so inequitably, our jails and prisons are full of people who’ve been treated poorly by the world. Compared to the average citizen, people in prison grew up with less money, received less education, experienced more trauma. And, no matter what people’s earlier lives were like, if they’re in prison, they’re not being treated well now.
So they have a lot of justifiable grievances against the dominant political, cultural, and religious beliefs of our country. Punished unfairly by their fellow Christians, people sour on Christianity. Inside walls where the demographics make it blatantly obvious that our laws are enforced in a malignantly racist way, racial tensions boil.
At Pages to Prisoners, an organization that sends free books to people inside, we get requests for stuff about Norse mythology, Odinism, and Asatru. Lots of folks ask for material to learn foreign languages – people want to feel like they’ve accomplished something during their time in prison – but I always feel skeptical when somebody wants help learning Icelandic.
Not that there’s anything wrong with Icelandic. And Norse mythology is cool! Unfortunately, a gaggle of violent white supremacists decided that Norse mythology should be the basis for their religion. Starting in the 1970s, a right-wing racist from Florida began sending “Odinist” publications into prisons.
During the thirteenth century, Christian scholars transcribed many of the old Norse myths so that they could better understand the literary allusions of old Icelandic poetry. But they didn’t record anything about ancient religious practice. We barely have any information about most ancient pagan beliefs. Anyone who wants to adopt a pre-Christian European religion now – whether it’s Wicca, Druidism, Odinism, or Celtic polytheism – is basically forced to make things up.
I have nothing against religious invention. All religions were made by human beings – there’s no a priori reason why a religion created long ago, by people who understood much less about the world than we do now, would be better than something you invent today. Sure, ancient religions have been tested by time, suggesting that they possess virtues that their practitioners found helpful over the years, but most ancient religions have their problems, too. Inaccurate cosmologies, scattered hateful passages in their texts, that sort of thing.
So I like the idea of neo-paganism. You want to find a clearing in the woods and
do some moonlit dancing? You’d rather
worship a feminine generative force than a norm-enforcing patriarchal deity? You want to exalt nature as a hearth to be
protected rather than a resource to be exploited? Go right ahead! All of that sounds pretty great to me.
Unfortunately,
neo-paganism as it’s currently practiced in prison tends to be pretty hateful.
That’s why I’ve been
working on a set of anti-racist pamphlets about Norse mythology. Currently, when people ask for The Poetic
Edda or whatever, we send a friendly letter saying that we don’t have it,
and also that we generally don’t stock that sort of thing because it runs afoul
of our anti-hate policy.
But the Norse myths are
certainly no more hateful than Biblical myths, and we send plenty of
those. The main difference is that
centuries of continued Christian practice have created a scaffolding of gentler
beliefs around the stories in the Bible.
The text of Psalm 137
states that “Happy shall he be, that taketh and dasheth thy little
ones against the stones.” But the
text is a tool, not the entirety of the religion. The practice of Christianity frowns upon
the murder of any human infant. Whether
you like the kid’s parents or not.
We’d be better off if Pages to Prisoners could send warm-hearted material about Norse mythology to people. Sure, you can interpret the Norse myths as endorsing a war-mongering death cult. You can interpret the Old Testament that way, too. But you can also interpret the Norse myths as environmentalist. Feminist. Supporting the pursuit of knowledge. Judging strangers based upon their merits, not their appearance.
Because contemporary
Odinism is so entangled with white supremacy, though, our pamphlet will have to
address skin color and genetic heritage directly. It’s a fraught topic. Lots of people in the U.S. don’t like any discussion
of evolution. Some people feel squigged
out when they learn that contemporary birds evolved from the same set of common
ancestors as the dinosaurs. And that’s far
less emotionally charged than a description of human evolution.
Plus, skin color still has huge implications for how people are treated in the United States. Consider, um, those prison demographics I cited above. And so discussions about the evolution of epidermal melanin concentrations are especially tense. Although the underlying biology is simple – some places have more sunlight than others! – because people think it matters, it does.
I’ve found that these conversations are actually a decent way to get people interested in the study of archeology and biology, though. After we’ve discussed this in jail, people have asked me to bring research papers and textbooks so that they could learn more.
Whenever two groups of an organism stop mating with each other, they’ll slowly drift apart. This rift might occur because the groups became physically separated from each other. Maybe one group migrated to an island. In contemporary times, maybe the groups were separated when humans built a new highway bisecting a habitat. Maybe two sets of similar-looking insects mate apart because they’re eating fruits that ripen at different times.
Or the groups might stop mating with each other because a chance mutation caused members of one group to want their sexual partners to smell a certain way. Various species of stickleback are able to interbreed – they identify other members of their kind based on smell. But water pollution has overwhelmed the fishes’s senses, leading the fish to mate indiscriminately.
If humans hadn’t
polluted their waters, though, these sticklebacks would have drifted farther
and farther apart until it became impossible for them to interbreed. No matter how many sense-suppressing
chemicals we dumped.
We don’t know what caused the initial rift between our ancestors and the ancestors of contemporary chimpanzees. About 4 million years ago, though, these groups stopped having children together. By 2 millions years ago (at least 100,000 generations later), these groups looked quite different from each other. Although it’s possible that these organisms could have still mated with each other and raised viable progeny, they rarely did.
One group of these
creatures, which included our ancestors, had a tucked pelvis and mostly upright
posture. This allowed for a good vantage
while scavenging and, eventually, hunting.
The other group, which includes chimpanzees’ ancestors, mostly moved on
all fours. This body plan results in
fewer mothers dying during childbirth.
As ever, there are trade-offs to be made.
Up until about 2 million
years ago, all our ancestors lived in Africa.
But then they began to migrate.
Over the next million years, they explored much of the globe. By about 500,000 years ago, half a dozen
different types of humans lived in Africa, Europe, and Asia. The difference between one population to the
next was not like the racial differences among contemporary humans, but more
like the difference between lions and tigers, or between polar bears and brown
bears. Scientists describe them as
distinct species. Although they were
similar enough that they could have sex and raise children together, they
rarely did – they lived in distinct parts of the world and had begun to evolve
adaptations to their specific environments.
Evolution isn’t easy. Nor is it quick. Just because a certain trait would be
advantageous doesn’t mean that creatures will acquire it. In the desert, it would help to have
adaptations for water retention like camels, or long ears like jackrabbits to
cool the blood. But a trait can only
spread after a random mutation creates it.
And, even if a trait is very helpful, if only one individual is born
with the adaptation, there’s no guarantee that it will have enough children for
the benefit to spread through the population.
Once a beneficial trait has a good toe-hold – present in perhaps 1% to 10% of the population – then we can expect it to flourish. But below that amount, even great adaptations might die off due to bad luck. That’s why it takes so many generations – tens of thousands, or hundreds of thousands – before you see organisms become drastically better suited for the environment. Even when scientists do directed evolution experiments in the lab, it takes about this many generations for a population of bacteria to evolve ways to consume a new food source, for instance.
By 500,000 years ago, the various species of humans were recognizably different. Denisovans lived in the mountains, and their hemoglobin genes allowed them to avoid altitude sickness. Their blood was less likely to clot and cause strokes, and they could extract more oxygen from the thin air. These are incredibly beneficial traits. Even though the Denisovans went extinct about 40,000 years ago, about 40% of people currently living in Tibet have copies of the Denisovan hemoglobin gene.
Our ancestors migrated east to the Denisovans’ homeland just before the Denisovans went extinct. To be perfectly honest, we probably killed them. But before or during this genocide, a few of our ancestors must have had sex with the locals. And then the bi-racial children of these Homo sapiens / Denisovan couplings must have been significantly better off for the gene to spread so widely.
The Neanderthal lived at
high latitude. Over many generations,
their average skin color became paler.
In part, this was probably due to the lack of selective pressure. Think about a dodo – there was no advantage
for these birds to lose their fear of humans.
But, because the dodos were living on an island that no humans traveled
to, there was also no harm in the birds becoming fearless.
Dodos lost a beneficial
trait – fear – because their fear wasn’t actively needed. It’s kind of like the airbags in an old
car. If your car’s engine goes bad,
you’ll notice right away. Turn the key,
hear it sputter. You use the engine
every time you drive. But your airbags
could get worse without you noticing … and then, in the moment when they’re
needed, they won’t deploy.
Humans living near the equator need epidermal melanin. If you don’t have enough melanin, you’ll get sunburns, which exacerbate the risk of infection and dehydration; you’ll suffer radiation-induced DNA damage, which leads to skin cancer; and you’ll lose folate, which means that pregnant women will have more birth defects.
The most recent ancestors
that humans and chimpanzees shared in common had pale skin. Contemporary chimpanzees are still pale. They can afford to be – their fur protects
them from the sun. But our ancestors
lost their fur, probably so that they didn’t overheat while running, and this
led to the evolution of dark skin.
High concentrations of
epidermal melanin distinguished humans from the other apes.
As humans migrated to
higher latitudes, though, they gradually lost this indicator of their
humanity. Because the sunlight was less
intense, there was less selective pressure.
Humans could lose their epidermal melanin in the same way that dodos
lost their fear – not because it was helpful to go without it, but because the
trait went untested in their day to day lives.
They had no way to “realize” how important it was.
Your airbags aren’t
helpful until you crash. And then
they’ll either deploy and save you, or they won’t.
Now, it’s possible that the Neanderthal also experienced some positive selective pressure on their skin color as they migrated north. Over thousands of generations, the Neanderthals may have benefited from paler skin because it increased their production of vitamin D. We don’t know for certain that the Neanderthal felt any evolutionary pressure to have more vitamin D – after all, contemporary Inuit people live at very high latitudes but still have a lot of epidermal melanin – but it’s true that vitamin D deficiency is a big risk among people with crummy diets.
In the past, hunter / gatherers typically ate much healthier, more varied diets than farmers. When humans began to farm, they would mostly eat the one type of plant that they cultivated, rather than the wide mix of plants that could be found growing wild. And when Homo sapiens farmers migrated to northern Europe, their diets were so poor that they even developed loss-of-function mutations in a cholesterol synthesis gene, probably so that they’d have higher concentrations of vitamin D precursors. Among these people, pale skin was probably a big advantage. They’d be ready for the cloudless days when their homeland’s feeble sunlight was enough to make some vitamin D.
Pieter Bruegel the Elder’s The Harvesters.
Around 40,000 years ago,
our planet’s most recent ice age ended.
The world began to warm, and glaciers retreated from Europe. By then, a group of humans living in Africa
were recognizably Homo sapiens.
These were our ancestors. Every
human alive today – no matter what you look like or where your family is from –
is descended from this group of people from Africa. They lived in tribes of twenty to a hundred
people, had darkly pigmented skin, made art, and spoke complex languages.
As the world warmed, some
of these Homo sapiens began to migrate.
These journeys occurred over many generations. Some tribes stayed in Africa; some tribes
ventured north into Europe; others moved east toward Asia. As they traveled, they encountered the humans
who already lived in those places. As
I’ve mentioned, the newcomers occasionally had sex and raised children with the
natives. They probably also killed a lot
of them. Unfortunately, we Homo
sapiens don’t have the best reputation for treating strangers well.
Interbreeding happened
rarely enough that most people living today have about 99% Homo sapiens DNA. Some people, especially if their families are
from Africa, have essentially 100% Homo sapiens DNA. At other extreme, even people whose families
are from Europe have 96% or more Homo sapiens DNA.
Among people living in
Tibet, the Denisovan hemoglobin gene is common, but most other Denisovan genes
are gone.
Like the Neanderthal
before them, the Homo sapiens who ventured north into Europe began to
lose their epidermal melanin. People who
hunted and fished probably became paler simply because there was less risk of
sun damage. Remember, this didn’t happen
all at once. Average skin color would
change only over the course of hundreds or even thousands of generations, not
during the course of a single journeying Homo sapiens’s lifetime.
Our ancestors spent almost
all their time outdoors, which is why even dark-skinned people could probably
synthesize plenty of vitamin D. Among
contemporary humans, vitamin D deficiency is such a big problem because we
spend too much time inside. As I type
this, I’m sitting at a table in the YMCA snack room, lit up by flickering
fluorescent bulbs. This low-quality
light won’t help me make vitamin D.
Instead, I take a daily
supplement. But that doesn’t come near
matching the health and psychological benefits of time outdoors.
Perhaps it’s worth mentioning that people in jail – places not known for providing a rich, high-quality, varied diet – typically get to go outside no more often than once a week. At our local jail, their hour of “outdoor rec” occurs in a little courtyard at the top of the jail, a cement space covered with a chain-linked fence. Outdoor rec often happened at night – a friend who was recently released told me that “This was still nice. You could see some stars. And there’s that restaurant, Little Zagrib, down the street? Sometimes we’d smell foods from their kitchen.”
Treating people that way
is unlikely to help them get better.
But back to our migrants! Descendants of these pale-skinned Homo sapiens continued to explore new territories. Some reached North America about 12,000 years ago, and some of their descendants continued farther, all the way to South America.
As people traveled –
journeys that lasted many generations – they continued to evolve. Indeed, skin color was a trait that came
repeatedly under selective pressure. As
people migrated south into the Americas, they were living progressively closer
and closer to the equator. Compared to
their grandparents, they were bombarded by more intense sunlight. They needed more epidermal melanin.
This is a process that
takes a long time. A family might have
six kids; maybe the two palest kids get sunburned, which makes it more likely
that they’ll develop skin infections and die before they have children of their
own. If this happens again and again,
among many different families, then eventually the whole population will wind
up with slightly darker skin.
A prediction for the distribution of human skin colors based on the intensity of ultraviolet light present at each latitude. Figure from Nina Jablonski & George Chaplin, “The Evolution of Human Skin Color,” in Journal of Human Evolution, 2000.
This figure depicts the (limited) data we have on the distribution of human skin colors before the modern era’s horrific set of forced migrations. In this image, white-colored regions indicate an absence of data, not low concentrations of epidermal melanin among a region’s prehistoric population. Figure from Nina Jablonski & George Chaplin, “The Evolution of Human Skin Color,” in Journal of Human Evolution, 2000.
Because human skin color
has changed during each of the many prehistoric migrations, it isn’t correlated
with other traits. As we entered the
modern era, people’s skin color was lighter or darker based on how close to the
equator their recent ancestors lived.
But human populations migrated so often that there were many different
groups, each with unique cultural and genetic heritages, living at every
latitude. Because skin color is so
closely linked to latitude, this means many different groups shared similar
concentrations of epidermal melanin. And
there’s no evolutionary pressure linking a trait that protects skin to brain
size or intelligence.
As it happens, there are
major events known to have caused a decrease in human brain size (and probably
intelligence). After all, human brains
are costly. Even though there’s a
benefit to being clever, there’s also been constant evolutionary pressure against
large brains.
Large brains kill
mothers. Because humans walk upright,
childbirth is riskier for human mothers than for other primates. Our posture constrains the width of our hips
– both male and female – but a baby’s whole head has to pass through that
narrow passageway.
Having children is so
risky that we evolved to give birth about 3 months prematurely. Human gestation takes about a year, but most
mothers give birth after only 9 months.
This allows a baby’s head to continue to grow outside the mother’s body,
but human babies are totally helpless at birth.
We have to be very devoted parents to keep them alive.
Also, our brains require a
lot of fuel. Human evolution occurred
over such a long, long time that our ancestors lived through many droughts and
calamities. During the hard years, our
ancestors would struggle to get enough to eat, and a large brain makes that
struggle harder.
A person with a smaller
brain requires fewer calories, making that person less likely to starve in lean
times. And, again, it’s worth
remembering that evolution happens over so many generations, among so many
families, that even small changes can add up.
If mothers who have small-headed children can survive a dozen
pregnancies, but mothers with large-headed children die after only a few, then
the trend will be to have people with smaller brains. Intelligence has to be extremely
beneficial to overcome this sort of evolutionary pressure.
Similarly, if people with
small brains are more likely to survive and raise children during droughts,
then, after hundreds of generations of people who have survived dozens of
extended droughts, you’d expect to see more people with small brains.
Many of us have the bad
habit of reflexively thinking about evolution as the gradual development of
more and more complexity. But that’s not
what it is. Evolution is the process by
which things that are better suited for their environment become more
abundant. If the environment is a hard
place to live in, then evolution tends to push for more and more simplicity. When it’s hard to get enough calories, why
waste calories on anything that you don’t really need?
Starfish are descended
from organisms that had brains. But
starfish are brainless. The ancestral
starfish that weren’t wasting energy thinking were more likely to survive.
Which should make you feel
pretty good about your own brain, actually.
Your ability to think is so fabulous that your ancestors evolved larger
and larger brains … even though these brains were sometimes causing us to
starve to death, or kill our mothers.
That’s a valuable thing
you’ve got inside your skull. It cost
our ancestors so much for you to be able to have it.
But, right. Because the cost was so high, human brains did shrink sometimes. Like when we first domesticated dogs. Our ancestors began living with dogs about 30,000 years ago. Dogs were willing to do some thinking for us – they’d sniff out prey and listen for predators at night. Based on the behavior of my family’s dogs, I bet that they licked the faces of screaming children. Maybe that doesn’t seem essential for survival, but I certainly appreciate every time our dogs calm the kids down.
Because we could slough
off a few mental tasks – I don’t need to be so observant if the dog will
help me hunt – our brains could shrink, making childbirth less deadly and
reducing the caloric cost of maintaining our minds each day.
When humans switched from hunting and gathering to agriculture, our brains shrunk further. A hunter / gatherer has to know so much about every plant and animal living nearby; the work asks more of a person’s brain than farming. This evolutionary trend was exacerbated by the fact that people’s diets became way worse when they began to farm. Instead of getting nutrition from a wide variety of different plants and animals, a farmer might eat meals consisting mostly of a single type of grain.
There’s nothing we can do now about these evolutionary trends. Dogs and farming swayed our ancestors’ evolution toward smaller brains, but it’s not as though you can get those neurons back by deciding to take up hunting, or never living with a pet.
But, honestly, our brains are so plastic that our genetic heritage matters less than how we choose to spend our time. By nature, neither gorillas nor parrots will speak human language. But individuals from both these species have been able to learn to communicate with us after we taught them.
Nobody is born with an
innate understanding of mythology, religion, science, or mathematics. None of that can be encoded in your
genes. If you want to understand this
stuff, you’ll have to make an effort to learn it.
Neuron count only suggests
a brain’s potential. You could do
incredible things with a low number – consider, by ways of analogy, the feats
that 1960s NASA accomplished using computers much smaller than a contemporary
telephone. And, conversely, sensory
deprivation will make it much harder to get things done, no matter what your
innate potential.
That’s why I volunteer with Pages to Prisoners. Our brains are capable of wonders. At any age, we can learn and grow. And yet, we lock people into prisons that seem designed to make them worse.
I am
descended from the oppressors. My
ancestors ventured from their homeland with colonial aspirations and genocidal
results.
It wasn’t my fault. I wasn’t born yet! But, having inherited vast privilege, some measure of responsibility from the misdeeds of my people surely falls upon my shoulders.
A hundred thousand years ago, several species of humans shared our planet. My ancestors, who would give rise to contemporary Homo sapiens, mostly lived in Africa. They differed from other primates in that their brains were larger, their posture more upright, their epidermis darker in hue, their verbal communication more nuanced.
During a period of climate change, my ancestors left their home. The planet was warming; glaciers receded; Homo sapiens ventured north.
Europe was already populated by humans, people who had weathered the bitter cold through the waning ice age. But my ancestors were undeterred. They did not respect the old territorial boundaries. Soon they supplanted the native peoples. Every last one of the natives died. Their people disappeared from the face of the earth, extinct.
Every time my ancestors ventured to a new land, the old inhabitants were killed. Nearly all of our planet’s large animals are gone now; megafauna extinction is directly correlated with human migration.
If it’s any consolation, Homo sapiens were not the only perpetrators of these atrocities. Every other human species – including those whom my ancestors harried to extinction – wrought similar devastation on their environments.
In this case, no reparations are possible. The victims are dead; their families curtailed. My ancestors’ misdeeds against them ceased, but only because there was no one left to harm.
But I can atone through remembrance.
And so, as a descendant of the oppressors, I felt a special sympathy toward the Neanderthal. When I was in school, these humans were consistently described as brutish, uncouth, and unintelligent. But I recognized that sort of language. My people have almost always maligned supposed “others” – until we took the time to learn how smart they are, all non-human animals were imagined to be unthinking automata. Pale-skinned Europeans claimed that intelligence – or even humanity itself – was inversely correlated with epidermal melanin concentration (by which measure Pan troglodytes would be more human than any Englishman).
Forty years ago, medical doctors implied that men who felt a sexual attraction to men differed from their peers on a cellular level, as though the human immunodeficiency virus was sensitive to a psychological preference. Even now, many medical doctors believe that people with higher amounts of epidermal melanin experience pain differently.
My people’s negative assessment of the Neanderthal, I figured, was probably not true. Indeed, in recent years we’ve discovered that Neanderthals made art, that they probably had spoken languages … that they were like us. Enough so that many humans living today carry Neanderthal DNA sequences in their genomes.
A Neanderthal model at Zagros Paleolithic Museum, Kermanshah. Photograph by ICHTO on Wikimedia Commons.
Inspired by Paul Kingsnorth’s The Wake, a first-person perspective of the apocalypse wrought upon 11th century England, I began working on a story narrated by the last of the Neanderthal.
I was still working on this story during the 2016 presidential election. But with our 45th openly praising white supremacists, I felt suddenly less inspired to celebrate the Neanderthal. Many of the hate mongers were extolling the virtues of humans descended from northern Europeans, and, as it happens, these are the people who have the most abundant remnants of Neanderthal DNA in their genomes.
Genetics isn’t destiny. And there haven’t been any correlations between Neanderthal DNA and intelligence; indeed, most of the genetic sequences that have been proposed to modulate intelligence are probably false. Neanderthal DNA has been found to correlate only with an increased risk of depression and an increased susceptibility to allergies.
I began working on my Neanderthal story as an apology to the dispossessed, but I couldn’t bring myself to finish it in an environment where some individuals might tout their Neanderthal heritage as a mark of superiority. As though their blood conferred the right to mistreat people from other backgrounds, or the right to so thoroughly ravage our planet’s atmosphere that other people’s homes are scorched or submerged beneath the sea.
Which
seems shocking to me. Quite recently,
the Neanderthal were thoroughly impugned.
As though we could declare their kind to be undeserving of existence and
thereby spare ourselves a reckoning for having killed them.
Now the
contemporary oppressors herald the Neanderthal as a source of greatness. Light-skinned warrior folk, beset by
dark-skinned immigrants from the south.
Who
would have thought?
Then again, I would not have expected Odin or Thor to become patron deities of U.S. white supremacists. Nor that they might switch from beer to chugging milk as a display of inner fortitude.
Hate
works in mysterious ways.
Someday, perhaps, in a kinder, gentler world, I’ll feel safe to write more stories featuring the Neanderthal. For now, I’ve set my draft aside.
I was planning an essay on cell phones and surveillance. The central thesis was that our Supreme Court is a massively flawed institution. Many of our current Supreme Court justices are both willfully ignorant and opportunistically illogical. This set of people are not exceptionally knowledgeable, nor are they particularly clever. But we have given them extraordinary power to shape our world.
I will still write that essay – Carpenter v. United States is definitely worth discussing – but shortly after I prepared my outline, the Supreme Court released a slew of misguided, malicious decisions. And then Anthony Kennedy – who is already a pretty crummy jurist – announced his resignation. A narrow-minded ideologue will be nominated to replace him.
Last weekend, people gathered across the country to protest recent developments at our nation’s immigration detention centers. And I couldn’t help but think that the protesters’ energy and enthusiasm was misdirected.
Don’t get me wrong – wrenching families apart is awful. Every citizen of this country should feel ashamed that this is being done on our behalf, and we should want for it to stop. It’s worth being upset about, both these new developments at immigration detention centers and when families are severed because the parents were incarcerated for semi-volitional medical conditions like drug addiction.
(To be fair, living with addicts is often also horrible. It’s a point of pride among people in jail if they kept clean while their kids were young.)
In My Brother Moochie, Issac Bailey writes beautifully about the harms suffered by millions of families across the country:
As a member of the perpetrator’s family … you don’t know what you are allowed to feel, or think. Victims can mourn, and others will help them mourn. When prosecutors and pundits talk about justice, they are referring to victims and their families, not families like mine. Why should anybody give a damn that the ripple effects of crime change our lives, too? We don’t get to mourn. We don’t get to reflect, at least not fully, not publicly.
To stand by a man you love after he has done something dastardly is to be accused of having a lack of respect for what the victim has endured. To demand that he not be known solely by his worst act is to be accused of excusing evil. To not be there for him would feel like a dereliction of familial duty, a betrayal of the worst order. To state the truth – that sentencing him to a long stay behind bars would be a devastating blow to your family – is to open yourself up to ridicule and screams of, “He should have thought about that before he decided to kill a man.”
Although the numbers are smaller, what we’re doing at immigration detention centers is worse. The only “crime” that these people are accused of is fleeing torture, rape, and murder. They migrated to land controlled by the U.S. government too late – European immigrants already staked claims to territories by murdering the previous inhabitants. Those prior inhabitants had immigrated from Siberia and staked their claims by murdering dangerous macrofauna and their human competitors.
All claims of sovereignty, among almost all species, have involved violence. Even plants strangle their competitors, or steal sunlight, or waft poisons through the air.
But I digress. My worry isn’t philosophical. I’m simply afraid that horrendous abuses of power like what’s happening at the immigration detention centers will become tragically routine.
Lots of people voted for POTUS45 in the last presidential election, but demography is working against his political party. Through gerrymandering, a minority party can maintain control over democratically-elected legislative bodies for a long time. (Indeed, the electoral college is itself a form of gerrymandering, designed as a tool to suppress the influence of liberal northerners.)
But the Supreme Court is an even better tool for minority control. A mere quintet of hate machines can shape the entire country. Barring a constitutional amendment imposing term limits, or a wave of Supreme Court assassinations during the next administration, they will.
Given their fundamental misunderstandings regarding terms like “free market,” “privacy,” “speech,” and “person,” it will be pretty horrible.
As a member of the perpetrator’s family … you don’t know what you are allowed to feel, or think. Victims can mourn, and others will help them mourn. When prosecutors and pundits talk about justice, they are referring to victims and their families, not families like mine. Why should anybody give a damn that the ripple effects of crime change our lives, too? We don’t get to mourn. We don’t get to reflect, at least not fully, not publicly.
Frank Brown Cloud 
