Category: Evolutionary biology

On scientific misconceptions, Eurocentrism, and the evolution of skin color.

On scientific misconceptions, Eurocentrism, and the evolution of skin color.

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.)

For their 2022 study “Dairying, Diseases, and the Evolution of Lactase Persistence in Europe,” Evershed & colleagues looked at food residues stuck to ancient pottery and found that cows’ milk has been a major part of European diets for approximately 9,000 years. But these people couldn’t digest milk well. For their 2020 study “Low Prevalence of Lactase Persistence in Bronze Age Europe Indicates Ongoing Strong Selection over the Last 3,000 Years,” Burger & colleagues found that most of the dead warriors from an ancient European battleground did not have the genes for lactose tolerance.

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.

On eating plants.

On eating plants.

In the mid-1800s, Claude Bernard – the “father of experimental physiology” – began a series of experiments to create carnivorous rabbits.

Don’t worry: Bernard wasn’t cultivating predatory beasts like the angry rabbit in Monty Python and the Holy Grail. At first he was simply starving animals until their acidic urine indicated that they’d begun to consume their own flesh as fuel. Deprived of calories, any animal will metabolize its own muscle.

But Bernard went further. As he describes in An Introduction to the Study of Experimental Medicine (translated by Henry Copley Greene), Bernard felt that:

“A carnivorous rabbit had to be experimentally produced by feeding it with meat …”

“I had rabbits fed on cold boiled beef (which they eat very nicely when they are given nothing else). My expectation was again verified …”

“To complete my experiment, I made an autopsy on my animals, to see if meat was digested in the same way in rabbits as in carnivora. I found, in fact, all the phenomena of an excellent digestion in their intestinal reactions …”

This was a strange experiment. Claude Bernard did make a novel discovery, but I don’t think the gains were commensurate with the cost.

Bernard, however, was proud of his willingness to inflict pain for the sake of science. He had a reputation for live dissections of unanesthetized dogs; his spouse called him a monster, divorced him, and created France’s first animal welfare organization.

By all outward appearances, Bernard was unperturbed. He told his friends and colleagues that he’d only married that woman for her money, anyway, which he’d needed to build his first laboratory. By the time she left, she was of no further use to him. And he was disinterested in her “fashionable” morality.

In An Introduction to the Study of Experimental Medicine, Bernard writes that,

“A physiologist is not a man of fashion, he is a man of science, absorbed by the scientific idea which he pursues: he no longer hears the cry of animals, he no longer sees the blood that flows, he sees only his ideas and perceives only organisms concealing problems which he intends to solve.”

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Claude Bernard tortured animals, disdained Charles Darwin’s theory of evolution, and loathed the introduction of statistics into biological research. Still, the conclusion of Bernard’s rabbit experiment is correct.

Herbivores can digest meat.

And this transition – an herbivore switching to a meat-based diet – is far more common than its opposite. Plants are much more difficult to eat!

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Most species that we think of as herbivores will occasionally eat meat. Cows consume chickens, mice, dead rabbits (especially if the cows are mineral deficient, such as the experimental herds intentionally fed a low-phosphorous diet in the 1990s). Squirrels raid nests to eat baby birds. Pandas will eat roadkill if they can’t find enough bamboo.

After all, another animal’s body provides the full compliment of nutrients that an animal needs – it’s much easier to live as a mere meat refurbisher than to create your own animal body from scratch!

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In a research article published in 2019, “Evolution of Diet Across the Animal Tree of Life,” Christian Roman-Palaclos, Joshua Scholl, and John Wiens speculate that the very first animals were carnivores. They write that:

“Remarkably, our results suggest that many carnivorous animals alive today may trace this diet through a continuous series of carnivorous ancestors stretching back for >800 million years.”

Their data don’t actually support this claim. Roman-Palaclos, Scholl, and Wiens categorized the diets (herbivorous, carnivorous, or omnivorous) of a wide range of animal species and found that a statistical model in which the first multicellular animals consumed other heterotrophs would be mathematically parsimonious. Historically, it would take fewer genetic changes to produce our world if herbivory had evolved independently many times over.

But evolution tends to be quite rapid when organisms encounter an empty ecological niche, which is why we see sudden increases in diversity during periods following mass extinctions (like the “Cambrian explosion”) and when animals reach new islands. And we know that multicellular life arose multiple times – at the very least, happening independently in both plants and animals.

The earliest multicellular animals were probably simple aggregates of cells that failed to separate after dividing. Even after genes could cause intentional multicellular development, these early animals were probably blobby things that pursued the same diets as their single-celled precursors.

All told, many of the assumptions made by Roman-Palaclos, Scholl, and Wiens seem dubious at best.

And yet. It probably would have been easier for earliest animals to eat other heterotrophs than to eat autotrophs. Single-celled protists already liked to eat the autotrophs, so most autotrophs had defenses. The autotrophs might be toxic; their tasty molecules were hidden behind indigestible cell walls. If the first multicellular animal gobbled these up, it would’ve gotten such a bellyache!

Except, right. The first multicellular animal didn’t have a belly.

It would’ve gotten such a lysosome-ache!!

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In more recent evolution, herbivorous mammals often developed pretty major adaptations to accompany their diet. For instance, herbivores typically have more complicated teeth than carnivores – by chewing their food, herbivores can rupture a plant’s cell walls to access the nutrients inside. And instead of stealing a full compliment of essential amino acids and vitamins from another animal, an herbivore has to synthesize these inside its body. Biosynthesis of Vitamin B12 is pretty tricky – my cells certainly can’t do it. Can yours?

A human whose body contained only human cells could barely digest anything, and certainly not plants. Indeed, most human babies begin life this way – as wholly human. Newborns seem to have very few bacteria inside their bodies, and it’s difficult for newborns to digest anything other than milk.

Soon after birth, though, humans acquire a wide range of passengers. On the surface of our skin and throughout our intestines, we harbor bacteria, many of which are essential for our health. Our passengers interact directly with our brains: certain gut microbes make exercise more pleasurable; other gut microbes are so closely linked with mood & mental wellness that researchers are exploring ways to use them therapeutically.

Without the help of the bacteria who build empires inside our bodies, we would be miserable – achy, asthmatic, bloated, and mentally unsound. And also, yes – without their help, we could not eat plants.

How fortunate that we are not alone!

Header image credit: Darryl Leja for the National Human Genome Research Institute’s photostream on flickr.

On the apparent rarity of human-like intelligence.

On the apparent rarity of human-like intelligence.

Like many people, I have a weak grasp on long times. My family often visits a nearby pioneer reenactment village where the buildings and wooden gearworks of its water-powered corn mill are about two hundred years old; I feel awed. In Europe, some buildings are a thousand years old, which sounds incredible to me.

These are such small sips of evolutionary time.

Humans have roamed our world for hundreds of thousands of years. Large dinosaurs ruled our planet for hundreds of millions of years. Animals whom we’d recognize as Tyrannosaurus rex prowled for the final 2.5 million years of that, with their last descendants dying about 66 million years ago.

My mind struggles to comprehend these numbers.

I found myself reflecting on this after a stray remark in Oded Galor’s The Journey of Humanity: The Origins of Wealth and Inequality: “Why is such a powerful brain so rare in nature, despite its apparent advantages?”

Galor’s question seems reasonable from the vantage of the present. We live on a planet where 96% of the mammalian biomass is either our own species or prey animals we’ve raised to eat. The total mass of all surviving wild dinosaurs – otherwise known as “birds” – is less than a thirtieth the mass of humans. We’ve clearly conquered this world. Our dominance is due to our brains.

And this moment – right now! – feels special because we’re living through it. From a geological or evolutionary perspective, though, the present is a time much like any other. If we represent the total lifespan of our sun as a 24-hour day (which is much more sensible than representations with the present moment at the end of the day), the current time would be 10:58 a.m., and our sun will become so hot that it boils away all our planet’s liquid water at 7:26 p.m. Between now and then, though, we have a whole workday’s time for life to continue its beautiful, chaotic evolutionary dance. Perhaps quite soon – maybe just a million years from now, or 10 million, which is less than two minutes of our total day – the descendants of contemporary parrots, crows, or octopuses could become as intelligent as contemporary Homo sapiens.

As a human, I’m biased toward thinking that parrots and crows would have a better chance than octopuses – after all, these birds face a similar evolutionary landscape to my own ancestors. They’re long-lived, social species that invest heavily in childcare, are anatomically well-suited for tool use, and face few risks from predators.

Or rather, parrots would face few risks if humans weren’t around. Unfortunately them, a voracious species of terrestrial ape is commandeering their homeland and kidnaps their young to raise as pets. But crows can thrive in a human-dominated landscape – some crows even use our cars as tools, cracking nuts by placing them in urban crosswalks then retrieving their snack after the light turns red.

Octopuses, however, are short-lived and antisocial. They’re negligent parents. Their brief lives are haunted by nightmarish predators. And yet. Some octopuses are already quite intelligent; their intelligence appears to confer a reproductive advantage (if only by virtue of survival); their bodies are well-suited for tool use. Certain types of tools, like flaked stone, would be more difficult to create underwater, but many octopuses are capable of brief sojourns into open air. So I wouldn’t rule them out. Sometimes evolution surprises us – after all, the world has a lot of time to wait.

Which means that powerful brains like ours might not be rare in the future. Especially if our species does something stupid – like engaging in nuclear war, succumbing to global pandemic, or ruining crop yields with climate change – and the animal kingdom’s future intelligentsia don’t have to compete with 8 billion Homo sapiens for space and resources.

Also, it’s surprisingly difficult to assess whether powerful brains like ours were rare in the past. Intelligent, tool-crafting, fire-wielding, language-using species have gone extinct before – consider the Neanderthal. Our own ancestors nearly went extinct during past episodes of climate change, like after a volcanic eruption 70,000 years ago. And even if some species during the age of dinosaurs had been as intelligent as modern humans, we might not recover much evidence of their brilliance.

Please note that I’m not arguing that Tyrannosaurus rex wove baskets, wielded fire, or built the Egyptian pyramids. For starters, the body morph of T-Rex is ill-suited for tool use (as depicted in Hugh Murphy’s T-Rex Trying comics). But simply as a thought experiment, I find it interesting to imagine what we’d see today if T-Rex had reached the same level of technological and cultural sophistication as humans had from 100,000 to 10,000 years ago.

If T-Rex made art, we wouldn’t find it. The Lascaux paintings persisted for about 20,000 years because they were in a protected cave, but as soon as we found them, our humid exhalations began to destroy them. Millions of years would crush clay figurines, would cause engraved bone to decompose.

If T-Rex crafted tools from wood or plant fibers, we wouldn’t find them. We can tell that ancient humans in the Pacific Northwest of North America caught an annual salmon harvest by analyzing radioactive isotopes, but we’ve never found evidence of the boats or nets these ancient people used. After a few more radioactive half-lives passed – much sooner than a million years – this would have become invisible to us.

If T-Rex crafted tools from stone, we’d find remnants, but they’d be difficult to recognize. Evidence for human tool use often comes in three types – sharp flakes (usually 1-3 inch blades used as knives or spear tips), a hammer (often just a big round stone), and a core (a hunk of good rock that will be hit with the hammer to knock knife-like flakes off its surface). We’re most likely to realize that a particular rock was a human tool if it’s near a human settlement or if it’s made from a type of sediment rare in the location where contemporary archaeologists found it (which is why we think that an ancient primate took particular interest in the Makapansgat pebble).

Still, time is a powerful force. 66,000,000 years can dull the edges of a flake, or produce sharp rocks through mindless geological processes. It’s been difficult for archaeologists studying submerged sites in ancient Beringia – a mere 30,000 years old! – to know for certain whether any particular rock was shaped by human hands or natural forces. Other stone tools used by ancient humans look a lot like regular rocks to me, for example this 7,000-year-old mortar from Australia or these 9,000-year-old obsidian knives from North America. Ten million more years of twisting, compressing, and chipping might deceive even a professional.

And then there’s the rarity of finding anything from that long ago. Several billion T-Rex have tromped across the land, but we’ve only found as much as a single bone from a hundred of them. 99.999996% of all T-Rex vanished without a trace.

From those rare fossils, we do know that T-Rex brains were rather small. But not all neurons are the same. Work from Suzana Herculano-Houzel’s research group has shown that the number of neurons in a brain is a much better proxy for intelligence than the brain’s total size – sometimes a bigger brain is just made from bigger neurons, with no additional processing power. And the brains of our world’s surviving dinosaurs are made quite efficiently – “Birds have primate-like numbers of neurons in the forebrain.” **

We humans are certainly intelligent. And with all the technologies we’ve made in the past 200 years – a mere millisecond of our sun’s twenty-four hour day – our presence will be quite visible to any future archaeologists, even if we were to vanish tomorrow. But we do ourselves no favors by posturing as more exceptional than we are.

Animals much like us could have come and gone; animals much like us could certainly evolve again. Our continued presence here has never been guaranteed.

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** A NOTE ON NEURON COUNTS: many contemporary dinosaurs have brains with approximately 200 million neurons per gram of brain mass, compared to human brains with approximately 50 million neurons per gram of brain mass. A human brain has a much higher total neuron count, at about 80 billion neurons, than dinosaurs like African Gray Parrots or Ravens, which have about 2 billion neurons, but only because our brains are so much more massive. If the brain of a T-Rex had a similar composition to contemporary dinosaurs, it might have twice as many neurons as our own.

Of course, elephant brains also have three times as many neurons as our own — in this case, researchers then compare neuron counts in particular brain regions, finding that elephant brains have about a third as many neurons specifically in the cerebral cortex compared to human brains. For extinct species of dinosaurs, though, we can only measure the total size of the cranial cavity and guess how massive their brains would have been, with no indication of how these brains may have been partitioned into cerebellum, cerebral cortex, etc.

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Header image: a photograph of Sue at Chicago’s Natural History Museum by Evolutionnumber9 on Wikipedia.

On scientific beliefs, Indigenous knowledge, and paternity.

On scientific beliefs, Indigenous knowledge, and paternity.

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.

Such beliefs might have been common among ancient humans – from their behavior, it appears that contemporary chimpanzees might also hold similar beliefs – and were almost certainly widespread among the First Peoples of South America.

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

On dangerous air & the damnation of cyanobacteria.

On dangerous air & the damnation of cyanobacteria.

During the acute phase of the Covid-19 pandemic, I kept thinking of Margarita Engle’s poem “More Dangerous Air.” The title seemed particularly resonant, and its a beautiful poem about growing up in an atmosphere of fear.

Newsmen call it the Cuban Missile Crisis.

Teachers say it’s the end of the world.

Engle documents the way we might flail, attempting to protect ourselves & our loved ones. We know enough to be afraid; we don’t yet know enough to be safe.

Early in the pandemic, people left their groceries on the front steps for days before bringing the bags inside. A year in, we were still needlessly scrubbing surfaces with toxic chemicals.

#

During the missile crisis, school children practiced fire drills, earthquake drills, tornado drills, air raid drills. (They didn’t yet need the contemporary era’s most awful: the active shooter drills.)

Hide under a desk.

Pretend that furniture is enough

to protect us against perilous flames.

Radiation. Contamination. Toxic breath.

The blasts are dangerous. But warfare with atomic weapons is different from other forms of violence. A bomb might kill you, suddenly; the poisoned air might kill you, slowly; the poisoned ground might maim generations yet unborn.

Each air-raid drill is sheer terror,

but some kids giggle.

They don’t believe that death

is real.

Radiation is invisible. Marie Curie didn’t know that it would kill her. Rosalind Franklin didn’t know that it would kill her.

We know, now. At least, some of us do.

Others – including a perilously large cadre of politicians – still think we ought to stockpile a behemoth nuclear arsenal.

Nuclear bomb: photograph by Kelly Michals on flickr.

#

Viruses are invisible. And they act slowly. Breathe in an invisible virus; a week later, you might begin to cough; three weeks later, your cough might worsen; a month after that seemingly innocuous breath in which you sucked a microscopic package of genetic code into your lungs, you might be in the hospital, or worse.

Connecting an eventual death to that first dangerous breath is actually a tricky cognitive feat! The time lag confuses us. It’s much easier for human minds to draw conclusions about closely consecutive events – a vaccine followed within hours or days by fever or heart problems.

#

Greenhouse gases are also invisible. If we drive past a power plant, we might see plumes rising from the towers, but we can’t see poison spilling from our cars, our refrigerators, our air conditioners, our meals. This is just good food on a plate! It doesn’t look like danger.

But we are changing the air, dramatically, in ways that might poison us all. Or – which is perhaps worse – in ways that might not affect us so much, but might make this planet inhospitable to our unborn grandchildren. Perhaps we will be fine. It’s humans born twenty years from now, or fifty years from now, who will suffer more.

#

Each individual can take action. You, as an individual, could fly less, buy less, eat plants.

And yet.

You, as an individual, can only do so much.

When I hide under my frail school desk,

my heart grows as rough and brittle

as the slab of wood

that fails to protect me

from reality’s

gloom.

#

We aren’t the first. Go outside and look around – the vibrant bursts of summer green are delightfully entrancing.

Our minds are plastic things – we make ourselves through the ways we live – but certain scripts were sculpted by our ancestry. Over hundreds of millions of years, the bearers of certain types of brains were more likely to be successful in life.

Creatures like us – who need air to breath, water to drink, shelter from sun and cold – often feel an innate love for the way summer light plays over a heady mix of blue and green.

We need all that green. The plants, the trees, the algae: for humans to survive the climate crisis we’ve been making, we’re depending on them. We need them to eat carbon dioxide from the air, and drink in hydrogen atoms from water, and toss back oxygen for us to breathe.

We’ve been poisoning the air, and they might save us.

Which is ironic, in a way. Because all that green – they wrought our planet’s first global devastation.

Saving us all this time would be like a form of penance.

#

Early in our planet’s history, there was very little oxygen in the air. Which was a good thing for the organisms living then! Oxygen is a very dangerous molecule. When we fall apart with age, it’s largely because “oxidative damage” accumulates in our cells. When grocery stores market a new type of berry as a “superfood,” they often extol its abundance of “antioxidants,” small molecules that might protect us from the ravages of oxygen.

The first living organisms were anaerobic: they did not need, and could not tolerate, oxygen. They obtained energy from sulfur vents or various other chemicals.

But then a particular type of bacteria – cyanobacteria – evolved a way to eat air, pulling energy from sunlight. This was the precursor to modern photosynthesis. Cyanobacteria began to fill the air with (poisonous!) oxygen as waste.

Many years passed safely, though. There was abundant iron then, on land and in the seas – iron drew down oxygen to rust.

Approximately two billion years passed without incident. All that iron buffered our planet’s atmosphere! It must have seemed as though the cyanobacteria could excrete a nearly infinite amount!

But then they reached a tipping point. The iron had all become iron oxides. The concentration of oxygen in the air rose dramatically. This hyper-reactive poison killed almost everything alive.

#

Perhaps cyanobacteria were punished for what they’d done. By filling the world with oxygen, they enabled the evolution of organisms with higher metabolisms. Creatures who lived faster, shorter lives, turbocharged by all that dangerous air. And these creatures – our forebears – nearly grazed their enablers out of existence.

Cyanobacteria were once masters of the universe. Then they were food.

And they were imprisoned within the cells of plants. Look up at a tree – each green leaf is a holding cell, brimming with cyanobacteria who are no longer free to live on their own. Grasses, ferns, flowers – every photosynthetic cell home to perhaps dozens of chloroplasts, the descendants of those who caused our planet’s first mass extinction.

A few outlaws linger in the ocean. Some cyanobactera still pumping oxygen into the air, the lethal poison that’s gulped so greedily by human lungs. Their lethal poison now enables our growth, our flourishing, our reckless abasement of the world.

And we are poisoning the air in turn, albeit in a very different way. In our quest to use many years’ stored sunlight each year, we dig up & burn the subterranean remnants of long-dead plants. The prison cells in which cyanobacteria once lived and died, entombed for millions of years within the earth, now the fuel for our own self-imposed damnation. The concentration of carbon dioxide in the air is slowly rising. Our atmosphere is buffered; for a while, our world will seem unchanged. Until, suddenly, it doesn’t.

Some species, surely, will survive. Will thrive in the hotter, swingier, stormier world we’re making.

It likely won’t be us.

On magic.

On magic.

There’s broad scientific consensus that school closures hurt children, probably making a significant contribution to future increases in premature death.

There’s also broad scientific consensus that school closures – particularly elementary school closures – aren’t helpful in slowing the spread of Covid-19. Children aren’t major vectors for this virus. Adults just have to remember not to congregate in the teachers’ lounge.

Worldwide, a vanishingly small percentage of viral transmissions have occurred inside schools.

And … our district just closed in-person school for all children.

In-person indoor dining at restaurants is still allowed. Bars are still open.

Older people are sending a clear message to kids: “Your lives matter less than ours.”

#

For at-risk children, school closures are devastating. A disruption in social-emotional learning; lifelong education gaps; skipped meals.

But for my (privileged!) family, the closure will be pretty nice. I was recently feeling nostalgic about the weeks in August when my eldest and I spent each morning together.

Our youngest attends pre-K at a private school. Her school, like most private schools around the country, (sensibly) re-opened on time and is following its regular academic calendar.

My eldest and I will do two weeks of home schooling before winter break. And it’ll be fun. I like spending time with my kids, and my eldest loves school so much that she often uses up most of her energy during the day – teachers tell us what a calm, lovely, hard-working kid she is. And then she comes home and yells, all her resilience dissipated.

Which is normal! Totally normal. But it’s a little crummy, as a parent, to know you’ve got a great kid but that you don’t get to see her at her best.

Right now she’s sad about not going to school – on Monday, she came home crying, “There was an announcement that we all have to switch to online only!” – but I’m lucky that I can be here with her. Writing stories together, doing math puzzles, cooking lunch.

Maybe we’ll practice magic tricks. She loves magic.

#

Last month, I was getting ready to drive the kids to school. T. (4 years old) and I were in the bathroom. I’d just handed T. her toothbrush.

N. (6 years old) walked over holding a gallon-sized plastic bag.

“Father, do you want to see a magic trick?” she asked.

“Okay, but I have to brush my teeth while you’re doing it.”

“Okay,” she said, and opened the bag. She took out a multi-colored lump of clay. It was vaguely spherical. Globs of red, white, and blue poked up from random patches across the surface, as though three colors of clay had been haphazardly moshed together.

“So you think this is just this,” she said, but then …”

She took out a little wooden knife and began sawing at the lump. “This is just this?”, I wondered. It’s an interesting phrase.

Her sawing had little effect. The knife appeared useless. I’m pretty sure this wooden knife is part of the play food set she received as a hand-me-down when she was 9 months old. “Safe for babies” is generally correlated with “Useless for cutting.”

She was having trouble breaking the surface of her lump.

I spat out my toothpaste.

She kept sawing. She set down the knife and stared at the clay intently. A worthy adversary.

I stood there, watching.

She grabbed the knife again and resumed sawing. More vigorously, this time. She started stabbing, whacking. This was enough to make a tiny furrow. She tossed aside the knife and pulled with her fingertips, managing to pry two lobes of the strange lump away from each other.

“Okay,” she said, “it’s hard to see, but there’s some green in there.”

T. and I crouched down and peered closely. Indeed, there was a small bit of round green clay at the center of the lump.

“Wow!” exclaimed T. “I thought it was just a red, and, uh, blue, and white ball! But then, on the inside, there’s some green!”

“I know!” said N., happy that at least one member of her audience understood the significance of her trick. “And look, I might even get it back together!”

#

N. started performing magic when she was four. T. was asleep for her afternoon nap.

“Okay,” she said, “you sit there, and I’ll put on a magic show. Watch, I’ll make, um … this cup! See this cup? I’ll make it disappear.”

“Okay,” I said, curious. We’d just read a book that explained how to make a penny disappear from a glass cup – the trick is to start with the cup sitting on top of the penny, so that the coin looks like it’s inside the cup but actually isn’t.

I had no idea how she planned to make the cup itself disappear.

“Okay, so, um, now you’re ready, and …” she looked at the cup in her hands. Suddenly, she whisked it behind her back. And stood there, looking at me somberly, with her hands behind her back.

“I don’t have it,” she said.

#

Magic – convincing an audience to believe in an illusion.

This is just this.

I don’t have the cup – it’s gone.

Much of our Covid-19 response has been magic-based. We repeat illusory beliefs – schools are dangerous, reinfections are rare, death at any age is a tragedy – and maybe our audience is swayed.

But that doesn’t change the underlying reality.

The cup still exists – it was behind her back.

#

Everyone will die. Mortality is inescapable.

Our species is blessed with prodigious longevity, probably because so many grandmothers among our ancestors worked hard to help their grandchildren survive.

(The long lives of men are probably an accidental evolutionary byproduct, like male nipples or female orgasms. Elderly men, with their propensity to commandeer resources and start conflicts, probably reduced the fitness of their families and tribes.)

After we reach our seventies, though – when our ancestors’ grandchildren had probably passed their most risky developmental years – our bodies fail. We undergo immunosenescence – our immune systems become worse at suppressing cancer and infections.

We will die. Expensive interventions can stave off death for longer – we can now vaccinate 90-year-olds against Covid-19 – but we will still die.

Dying at the end of a long, full life shouldn’t feel sad, though. Everybody dies. Stories end. That’s the natural arc of the world.

What’s sad is when people die young.

Children will face the risk of dying younger due to unnecessary school closures.

Children will face the risk of dying younger due to unmitigated climate change.

Children will face the risk of dying younger due to antibiotic resistant bacteria.

These are urgent threats facing our world. And we’re not addressing them.

The cup is still there.

#

For my daughter, of course, I played along. I smiled, and laughed. She stood there beaming, holding the cup behind her back.

“Magic!” I said.

N. nodded proudly, then asked, “Do you want me to bring it back?”

It’ll take the same measure of magic to bring back schools.

On childcare.

On childcare.

After my eldest was born, I spent the first autumn as her sole daytime caretaker. She spent a lot of time strapped to my chest, either sleeping or wiggling her head about to look at things I gestured to as I chittered at her.

We walked around our home town, visiting museums and the library. I stacked a chair on top of my desk to make a standing workspace and sometimes swayed from side to side while I typed. At times, she reached up and wrapped her little hands around my neck; I gently tucked them back down at my sternum so that I could breath.

She seemed happy, but it felt unsustainable for me. Actually getting my work done while parenting was nigh impossible.

And so our family bought a membership at the YMCA. They offer two hour blocks of child care for children between six weeks and six years old.

The people who work in our YMCA’s child care space are wonderful. Most seem to be “overqualified” for the work, which is a strange thing to write. Childhood development has huge ramifications for both the child’s and their family’s whole lifetime, and child psychology is an incredibly rich, complex subject. Helping to raise children is important, fulfilling work. No one is overqualified to do it.

Yet we often judge value based on salary. Childcare, because it was traditionally seen by European society as “women’s work,” is poorly remunerated. The wages are low, there’s little prestige – many people working in childcare have been excluded from other occupations because of a lack of degrees, language barriers, or immigration status.

I like to think that I appreciate the value of caretaking – I’m voting with my feet – but even I insufficiently valued the work being done at our YMCA’s childcare space.

Each time I dropped my children off – at which point I’d sit and type at one of the small tables in the snack room, which were invariably sticky with spilled juice or the like – I viewed it as a trade-off. I thought that I was being a worse parent for those two hours, but by giving myself time to do my work, I could be a fuller human, and maybe would compensate for those lapsed hours by doing better parenting later in the day.

I mistakenly thought that time away from their primary parent would be detrimental for my children.

Recently, I’ve been reading Sarah Blaffer Hrdy’s marvelous Mothers and Others, about the evolutionary roots of human childhood development, and learned my mistake.

Time spent in our YMCA’s childcare space was, in and of itself, almost surely beneficial for my children. My kids formed strong attachments to the workers there; each time my children visited, they were showered with love. And, most importantly, they were showered with love by someone who wasn’t me.

Hrdy explains:

A team headed by the Israeli psychologist Abraham Sagi and his Dutch collaborator Marinus van IJzendoorn undertook an ambitious series of studies in Israel and the Netherlands to compare children cared for primarily by mothers with those cared for by both mothers and other adults.

Overall, children seemed to do best when they have three secure relationships – that is, three relationships that send the clear message “You will be cared for no matter what.”

Such findings led van IJzendoorn and Sagi to conclude that “the most powerful predictor of later socioemotional development involves the quality of the entire attachment network.”

In the United States, we celebrate self-sufficient nuclear families, but these are a strange development for our species. In the past, most humans lived in groups of close family and friends; children would be cared for by several trusted people in addition to their parents.

Kids couldn’t be tucked away in a suburban house with their mother all day. They’d spend some time with her; they’d spend time with their father; they’d spend time with their grandparents; they’d spend time with aunties and uncles, and with friends whom they called auntie or uncle. Each week, children would be cared for by many different people.

The world was a harsh place for our ancestors to live in. There was always a risk of death – by starvation, injury, or disease. Everyone in the group had an incentive to help each child learn, because everyone would someday depend upon that child’s contributions.

And here I was – beneficiary of some million years of human evolution – thinking that I’d done so well by unlearning the American propaganda that caretaking is unimportant work.

And yet, I still mistakenly believed that my kids needed it to be done by me.

Being showered with love by parents is important. Love from primary caretakers is essential for a child to feel secure with their place in the world. But love from others is crucial, too.

I am so grateful that our YMCA provided that for my kids.

And, now that they’re old enough, my kids receive that love from school. Each day when they go in, they’re with teachers who let them know: You will be cared for no matter what.

On apocalypse clocks.

On apocalypse clocks.

The world is complicated. There’s so much information out there, so much to know. And our brains are not made well for knowing much of it.

I can understand numbers like a dozen, a hundred. I can make a guess at the meaning of a thousand. Show me a big gumball machine and ask me to guess how many gumballs are in it, maybe I’ll guess a thousand, a few thousand.

But numbers like a million? A billion? A trillion? These numbers are important, I know. These numbers might be the population of cities, or of planets, or of solar systems. These numbers might be the ages of species or planets. These numbers might be how many stars are in the sky, or how many stars in the sky might harbor life.

These numbers don’t mean much to me.

I don’t think the problem is just my brain. I’m fairly good with numbers, relative to the average human. It’s been years since I’ve sat in a math class, but I can still do basic integrals and derivatives in my head.

Yet I can’t understand those big numbers. They don’t feel like anything to me.

So we make graphs. Charts. We try to represent information in ways that our meager human brains can grasp.

A good chart can be a revelation. Something that seemed senseless before is now made clear.

#

An apocalypse is a revelation. The word “apocalypse” means lifting the veil – apo, off; kalyptein, conceal. To whisk away the cover and experience a sudden insight.

An illustration that depicts information well allows numbers to be felt.

Often, though, we illustrate information and we do it poorly.

The scientific method is gorgeous. Through guesswork, repetition, and analysis, we can learn about our world.

But science is never neutral. We impart our values by the questions we choose to ask, by the ways we choose to interpret the world’s ever-oblique answers.

#

Geological time is often depicted as a clock. A huge quantity of time, compressed down into a 24-hour day. Often, this is done with the ostensible goal of showing the relative unimportance of humans.

Our planet has been here for a day, and humans appear only during the final two minutes!

Unfortunately, this way of depicting time actually overemphasizes the present. Why, after all, should the present moment in time seem so special that it resides at midnight on our clock?

The present feels special to us because we’re living in it. From a geological perspective, it’s just another moment.

#

In Timefulness, geologist Marcia Bjornerud writes:

Geologic textbooks invariably point out (almost gleefully) that if the 4.5-billion-year story of the Earth is scaled to a 24-hour day, all of human history would transpire in the last fraction of a second before midnight.

But this is a wrongheaded, and even irresponsible, way to understand our place in Time. For one thing, it suggests a degree of insignificance and disempowerment that not only is psychologically alienating but also allows us to ignore the magnitude of our effects on the planet in that quarter second.

And it denies our deep roots and permanent entanglement with Earth’s history; our specific clan may not have shown up until just before the clock struck 12:00, but our extended family of living organisms has been around since at least 6 a.m.

Finally, the analogy implies, apocalyptically, that there is no future – what happens after midnight?

#

Timefulness is a lovely book, but Bjornerud does not present a corrected clock.

And so I lay in bed, thinking. How could these numbers be shown in a way that helped me to understand our moment in time?

I wanted to fix the clock.

#

The first midnight is easy – the birth of our sun. A swirling cloud of gas condenses, heating as gravity tugs the molecules into more and more collisions. Nuclear fusion begins.

Gravity tugs molecules inward, nuclear explosions push them outward. When these are balanced, our sun exists. Twelve o’clock.

Two minutes later, our planet is born. Metal and water and dust become a big rock that keeps swirling, turning, as it orbits the sun. It’s warmed, weakly, by light from the sun – our star shone dimly then, but shines brighter and brighter every day.

Our sun earns low interest – 0.9% each hundred million years, hotter, brighter. But wait long enough, and a low interest is enough.

Someday, shortly before it runs out of fuel, our sun will be blinding.

By 12:18 a.m., there is life on Earth. We’ve found fossils that many billions of years old.

And at 7:26 p.m., there will be no more life. Our sun will have become so bright that its blinding light evaporates all the oceans. The water will boil so hot that it will be flung into space. The Earth will be a rocky desert, coated perhaps in thick clouds of noxious gas.

Currently, it’s 10:58 a.m.

The dinosaurs appeared 35 minutes ago. 9.5 minutes ago, all of them died (except the ancestors of our birds).

Humans appeared 1 minute ago.

#

So, we have 3.5 billion years remaining – another 8.5 hours on our clock – before we have to migrate to the stars.

Humans certainly can’t persist forever. Empty space is stretching. Eventually, the whole universe will be dark and cold, which each speck of matter impossibly far from every other.

But our kind could endure for a good, long while. Scaled to the 24-hour day representing the lifespan of our sun, we still have another 300 years before the universe goes dark.

So many stories could fit into that span of time.

#

It’s 10:58 a.m., and life on Earth has until 7:26 p.m.

Humans crept down from trees, harnessed fire, invented writing, and built rockets all within a single minute. Life moves fast.

Quite likely, life from Earth will reach the stars.

But it needn’t be us.

The dinosaurs were cool. They didn’t make it.

We naked apes are pretty cool, too. I love our cave drawings, art museums, psychedelic street art. Our libraries. But we’ve also made prodigious mounds of trash. We’re pouring plumes of exhaust into the sky as we ship giant flatscreen televisions from place to place.

We burn a lot of fuel for the servers that host our websites.

We humans aren’t the first organisms to risk our own demise by pumping exhaust into the atmosphere. The industrial revolution was fueled by ancient plants – our engines burn old sunlight. But many microbes are happy to eat old sunlight, too. These microbes also pump carbon dioxide into the air. They’ve warmed our planet many times before – each time the permafrost thawed, microbes went to town, eating ancient carbon that had been locked up in the ice.

Foolish microbes. They made the Earth too hot and cooked themselves.

Then again, the microbes may have more modest goals than us humans. We’ve found no fossils suggesting that the microbes tried to build spaceships.

For our endeavors, we’ve benefited from a few thousand years of extremely stable, mild climate.

We still have 8.5 hours left to build some spaceships, but a thirty second hot squall at 10:59 a.m. would doom the entire project.

So much time stretches out in front of us. We could have a great day. We, in continuation of the minute of humans who preceded us, and continued by the seconds or minutes or hours of humans who will be born next.

We shouldn’t let our myopic focus on present growth fuck up the entire day.

Honestly? My children are four and six. I’d be so disappointed if I took them for a hike and they guzzled all their water, devoured all their snacks, within the first minute after we left our house.

On octopuses and family gatherings.

On octopuses and family gatherings.

Recently, a dear friend sent me an article from Scientific American about the blanket octopus.

She and I had been discussing unusual animal mating, because that’s what you do, right? Global pandemic hits and you share freaky trivia with your friends.

Miniscule male anglerfish will merge with the body of a female if they find her, feeding off her blood. Deadbeat male clinginess at its worst.

Blanket octopuses also have extreme sexual dimorphism – a female’s tentacles can span seven feet wide, whereas the males are smaller than an inch.

But, wait, there’s more! In a 1963 article for Science magazine, marine biologist Everet Jones speculated that blanket octopuses might use jellyfish stingers as weapons.

While on a research cruise, Jones installed a night-light station to investigate the local fish.

“Among the frequent visitors to the submerged light were a number of immature female blanket octopuses. I dip-netted one of these from the water and lifted it by hand out of the net. I experienced sudden and severe pain and involuntarily threw the octopus back into the water.”

“To determine the mechanism responsible for this sensation, 10 or 12 small octopuses were captured and I purposely placed each one on the tender areas of my hands. The severe pain occurred each time, but careful observation indicated that I was not being bitten.

“The pain and resulting inflammation, which lasted several days, resembled the stings of the Portuguese man-of-war jellyfish, which was quite abundant in the area.”

tl;dr – “It really hurt! So I did it again.”

#

My spouse teaches high school biology. An important part of her class is addressing misconceptions about what science is.

Every so often, newspapers will send a reporter to interview my father about his research. Each time, they ask him to put on a lab coat and pipette something:

I mean, look at that – clearly, SCIENCE is happening here.

But it’s important to realize that this isn’t always what science looks like. Most of the time, academic researchers aren’t wearing lab coats. And most of the time, science isn’t done in a laboratory.

Careful observation of the natural world. Repeated tests to discover, if I do this, what will happen next? There are important parts of science, and these were practiced by our ancestors for thousands of years, long before anyone had laboratories. Indigenous people around the world have known so much about their local varieties of medicinal plants, and that’s knowledge that can only be acquired through scientific practice.

A nine month old who keeps pushing blocks off the edge of the high chair tray to see, will this block fall down, too? That’s science!

And this octopus article, published in the world’s most prestigious research journal? The experiment was to scoop up octopuses by hand and see how much it hurt.

It hurt a lot.

#

The article that I linked to earlier, the Scientific American blog post that my friend had sent me, includes a video clip at the bottom. Here’s a direct link to the video:

I should warn, you, though. The first section of the video shows a blanket octopus streaming gracefully through the ocean. She’s beautiful. But then the clip continues with footage of a huge school of fish.

Obviously, I was hoping that they’d show the octopus lurch forward, wielding those jellyfish stingers like electrified nun-chucks to incapacitate the fish. I mean, yes, I’m vegan. I don’t want the fish to die. But an octopus has to eat. And, if the octopus is going to practice wicked cool tool-using martial arts, then I obviously want to see it.

But I can’t. Our oceans are big, and deep, and dark. We’re still making new discoveries when we send cameras down there. So far, nobody has ever filmed a blanket octopus catching fish this way.

#

Every time I learn something new about octopuses, I think about family reunions.

About twenty years ago, I attended a family reunion in upstate New York. My grandparents were celebrating their fiftieth wedding anniversary. Many people were there whom I’d never met before, and whom I haven’t seen since. But most of us shared ancestors, often four or five or even six generations back.

And we all shared ancestors at some point, even the people who’d married in. From the beginning of life on Earth until 150,000 years ago, you could draw a single lineage – _____ begat ______ who begat ______ – that leads up to every single human alive today. We have an ancestor in common who lived 150,000 years ago, and so every lineage that leads to her will be shared by us all.

There’s also an ancestor that all humans alive today share with all octopuses alive today. So we could host a family reunion for all of her descendants – we humans would be invited, and blanket octopuses would be, too.

I would love to meet a blanket octopus. They’re brilliant creatures. If we could find a way to communicate, I’m sure there’d be lots to talk about.

But there’s a problem. You see, not everyone invited to this family reunion would be a scintillating conversationalist.

That ancestor we share? Here’s a drawing of her from Jian Han et al.’s Nature article.

She was about the size of a grain of rice.

And, yes, some of her descendants are brilliant. Octopuses. Dolphins. Crows. Chimpanzees. Us.

But this family reunion would also include a bunch of worms, moles, snails, and bugs. A lot of bugs. Almost every animals would’ve been invited, excluding only jellyfish and sponges. Many of the guests would want to lay eggs in the potato salad.

So, sure, it’d be cool to get to meet up with the octopuses, our long-lost undersea cousins. But we might end up seated next to an earthworm instead.

I’m sure that worms are very nice. Charles Darwin was fascinated by the intelligence of earthworms. Still, it’s hard to have a conversation with somebody when you don’t have a lot of common interests.

On empathy and the color red.

On empathy and the color red.

I can’t fly.

I try to feed my children every night, but I never vomit blood into their mouths.

When I try to hang upside down – like from monkey bars at a playground – I have to clench my muscles, and pretty soon I get dizzy. I couldn’t spend a whole day like that.

And, yes, sometimes I shout. Too often during the pandemic, I’ve shouted at my kids. But when I shout, I’m trying to make them stop hitting each other – I’m not trying to figure out where they are.

It’s pretty clear that I’m not a bat.

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Photograph by Anne Brooke, USFWS

Because I haven’t had these experiences, philosopher Thomas Nagel would argue that I can’t know how it feels to be a bat.

In so far as I can imagine [flitting through the dark, catching moths in my mouth], it tells me only what it would be like for me to behave as a bat behaves.

But that is not the question. I want to know what it is like for a bat to be a bat.

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Perhaps I can’t know what it feels like for a bat to be a bat. And yet, I can empathize with a bat. I can imagine how it might feel to be trapped in a small room while a gamboling, wiry-limbed orc-thing tried to swat me with a broom.

It would be terrifying!

And that act of imagination – of empathy – is enough for me to want to protect bats’ habitats. To make space for them in our world. Sure, you could argue that bats are helpful for us – they’re pollinators, they eat pesky bugs – but empathy lets us care about the well-being of bats for their own sake.

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Literature exercises our minds: when we read, invent, and share stories, we build our capacity for empathy, becoming more generally aware of the world outside our own skulls.

Writing can be a radical act of love. Especially when we write from a perspective that differs from our own. The poet Ai said that “Whoever wants to speak in my poems is allowed to speak, regardless of sex, race, creed, or color.” Her poems often unfurl from the perspective of violent men, and yet she treats her protagonists with respect and kindness. Ai gives them more than they deserve: “I don’t know if I embrace them, but I love them.”

Ai

That capacity for love, for empathy, will let us save the world. Although many of us haven’t personally experienced a lifetime of racist microaggressions or conflict with systemic oppression, we all need to understand how rotten it would feel. We need to understand that the pervasive stress seeps into a person’s bones, causing all manner of health problems. We need understand the urgency of building a world where all children feel safe.

And if we don’t understand – yet – maybe we need to read more.

Experiments suggest that reading any engaging literary fiction boosts our ability to empathize with others. Practice makes better: get outside your head for a while, it’ll be easier to do it again next time.

Of course, we’ll still need to make an effort to learn what others are going through. Thomas Nagel was able to ruminate so extensively about what it would feel like to live as a bat because we’ve learned about echolocation, about their feeding habits, about their family lives. If we want to be effective anti-racists, we need to learn about Black experiences in addition to developing our empathy more generally.

Luckily, there’s great literature with protagonists facing these struggles – maybe you could try How We Fight for Our Lives, Americanah, or The Sellout.

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As a bookish White person, it’s easy for me to empathize with the experiences of other bookish White people. In Search of Lost Time doesn’t tax my brain. Nor does White Noise. The characters in these books are a lot like me.

The cognitive distance between me and the protagonists of Americanah is bigger. Which is sad in and of itself – as high schoolers, these characters were playful, bookish, and trusting, no different from my friends or me. But then they were forced to endure hard times that I was sufficiently privileged to avoid. And so when I read about their lives, perched as I was atop my mountain of privilege, it was painful to watch Ifemelu and Obinze develop their self-protective emotional carapaces, armoring themselves against the injustice that ceaselessly buffets them.

Another reader might nod and think, I’ve been there. I had to exercise my imagination.

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In Being a Beast, Charles Foster describes his attempts to understand the lives of other animals. He spent time mimicking their behaviors – crawling naked across the dirt, eating worms, sleeping in an earthen burrow. He wanted a badger’s-eye view of the world.

Foster concluded that his project was a failure – other animals’ lives are just so different from ours.

And yet, as a direct consequence of his attempt at understanding, Foster changed his life. He began treating other animals with more kindness and respect. To me, this makes his project a success.

White people might never understand exactly how it feels to be Black in America. I’m sure I don’t. But we can all change the way we live. We can, for instance, resolve to spend more money on Black communities, and spend it on more services than just policing.

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Empathy is working when it forces us to act. After all, what we do matters more than what we purport to think.

It’s interesting to speculate what it would feel like to share another’s thoughts – in Robert Jackson Bennett’s Shorefall, the protagonists find a way to temporarily join minds. This overwhelming rush of empathy and love transforms them: “Every human being should feel obliged to try this once.”

In the real world, we might never know exactly how the world feels to someone else. But Nagel wants to prove, with words, that he has understood another’s experience.

One might try, for example, to develop concepts that could be used to explain to a person blind from birth what it was like to see. One would reach a blank wall eventually, but it should be possible to devise a method of expressing in objective terms much more than we can at present, and with much greater precision.

The loose intermodal analogies – for example, “Red is like the sound of a trumpet” – which crop up in discussions of this subject are of little use. That should be clear to anyone who has both heard a trumpet and seen red.

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We associate red with many of our strongest emotions: anger, violence, love.

And we could tell many different “just so” stories to explain why we have these associations.

Like:

Red is an angry color because people’s faces flush red when they’re mad. Red blood flows when we’re hurt, or when we hurt another.

Or:

Red represents love because a red glow spreads over our partners’ necks and chests and earlobes as we kiss and caress and fumble together.

Or:

Red is mysterious because a red hue fills the sky at dawn and dusk, the liminal hours when we are closest to the spirit world.

These are all emergent associations – they’re unrelated to the original evolutionary incentive that let us see red. Each contributes to how we see red now, but none explains the underlying why.

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We humans are blue-green-red trichromatic – we can distinguish thousands of colors, but our brains do this by comparing the relative intensities of just three.

And we use the phrase “color blind” to describe the people and other animals who can’t distinguish red from green. But all humans are color blind – there are colors we can’t see. To us, a warm body looks identical to a cold wax replica. But their colors are different, as any bullfrog could tell you.

Photograph by Tim Mosenfelder, Getty Images

Our eyes lack the receptors – cone cells with a particular fold of opsin – that could distinguish infrared light from other wavelengths. We mistakenly assume these two singers have the same color skin.

When we look at flowers, we often fail to see the beautiful patterns that decorate their petals. These decorations are obvious to any bee, but we’re oblivious. Again, we’re missing the type of cone cells that would let us see. To fully appreciate flowers, we’d need receptors that distinguish ultraviolet light from blue.

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Most humans can see the color red because we’re descended from fruit eaters. To our bellies, a red berry is very different from a green berry. And so, over many generations, our ancestors who could see the difference were able to gather more nutritious berries than their neighbors. Because they had genes that let them see red, they were better able to survive, have children, and keep their children fed.

The genes for seeing red spread.

Now, several hundred thousand years later, this wavelength of light blares at us like a trumpet. Even though the our ancestors learned to cook food with fire, and switched from fruit gathering to hunting, and then built big grocery stores where the bright flashes of color are just advertisements for a new type of high-fructose-corn-syrup-flavored cereal, red still blares at us.

Once upon a time, we really needed to see ripe fruit. The color red became striking to us, wherever we saw it. And so we invented new associations – rage, or love – even though these are totally unrelated to the evolutionary pressures that gave us our red vision.

Similarly, empathy wasn’t “supposed” to let us build a better world. Evolution doesn’t care about fairness.

And yet. Even though I might never know exactly how it feels when you see the color red, I can still care how you’re treated. Maybe that’s enough.

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Header image: a greater short-nosed fruit bat, photograph by Anton 17.