The Ape That Understood the Universe, Steve Stewart-Williams, Cambridge University Press, 387 pages

Blueprint: How DNA Makes Us Who We Are, Robert Plomin, The MIT Press, 280 pages

It’s possible for humans to change. In recent centuries we’ve lived as hunter-gatherers, as farmers, as factory workers, and as screen-absorbed technology drones—among much else. Different cultures do things in radically different ways even with the same technology. Specific individuals, too, change over the course of their lives and act differently in different environments.

And yet there are limits. Radical efforts at social engineering have resulted in starvation and mass killings. While we don’t like to think about it, some people seem naturally capable of things that others simply are not. As a result, one of the biggest questions in politics is how greatly we can reorganize and equalize society without bashing our heads into the limits of nature.

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Two new books lay out the current science on human nature and human variation. In The Ape That Understood the Universe, psychology professor Steve Stewart-Williams explains the evolutionary roots that underlie many of our most fundamental instincts and behaviors. And in Blueprint, behavioral geneticist Robert Plomin lays out the wealth of evidence we have that differences among individuals often boil down to differences in their DNA. Together, they challenge major strains of liberal and conservative thought alike.

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Stewart-Williams begins with the very basics of evolution, paying special attention to the “selfish gene” theory most famously articulated by Richard Dawkins. Essentially, genes exist to replicate themselves, and those that do so most efficiently are the ones that spread. They do this primarily by helping their host—living things—survive, reproduce, and help their relatives reproduce, by any means necessary. The life around us is the result of this process playing out over millions of years, with changes introduced through random genetic mutations and shaped by natural selection in each unique environment.

That’s the part that annoys some conservatives. Here’s the part of Stewart-Williams’s thinking that offends the Left: our brains, no less than our arms and our legs, are the result of evolutionary processes. We are programmed with a suite of instincts and urges that impel us to behave in ways that have been successful for humans in the past. This includes not just the basic drives like hunger, but also a lot of preferences and behavioral patterns that many would prefer to see as mere outgrowths of culture, malleable as clothing styles. Perhaps most controversially, it includes biological differences between the sexes.

Stewart-Williams’s field, evolutionary psychology, has its share of critics—those who point out that one can come up with an evolutionary “just-so story” to explain just about anything humans do. But as Stewart-Williams shows, the essential findings of evolutionary psychology have far stronger support than mere conjecture.

How could we possibly know if a behavior is part of our very nature, instead of springing from culture? One powerful indicator is whether it is a human universal; if, in all the world, there is no society where something is different, that suggests it may be hardwired. (This is especially true if it persists despite cultural efforts against it.) Another is whether our behaviors echo those found in other species facing similar situations. And yet another is whether they have a clear connection to evolutionary fitness—in other words, whether it’s the kind of thing that would evolve.

These are the lenses through which Stewart-Williams looks at an astonishing variety of human tendencies, carefully evaluating the theories and evidence as to how they came about and sorting through the inevitable evolutionary riddles and controversies—ranging from altruism to group selection to nepotism to sexual attraction and jealousy. He also catalogues ways in which our evolved desires, including our insatiable taste for sugar, can be an awkward and unfortunate fit for the modern world.

And of course, he spends some time on sex differences too, starting with a handy list of 10 commonly found in nature and noting that many are found among humans too. For instance, men are physically larger than women, have more interest in casual sex, are more likely to “pay” for it (literally and figuratively), do less child care, grow up more slowly, and don’t live as long. His thorough exploration of these phenomena leaves little doubt that biology plays a role in them.

But all this focus on evolution doesn’t lead Stewart-Williams to neglect the power of culture—quite the opposite, in fact. He notes that our sexual nature leaves plenty of flexibility for different mating systems, from monogamy to polygamy to casual flings. And the end of the book is dedicated to the concept of “memes,” the ideas and practices that spread from person to person, from songs to cooking techniques to scientific theories. These work similarly to genes in a key way—if they don’t succeed in replicating themselves and spreading, they die out—and yet their power reveals how much of the human experience is not hardwired, but instead depends on what one’s fellow humans have been up to. And it turns out that memes are the subject of a scientific literature considerably deeper than one might expect.

This is not a perfect book; in particular, some of the writing is a bit hokey, including a lengthy exercise near the beginning in which we imagine aliens coming to Earth to study the human species. But it’s worth getting over that. Simply put, The Ape That Understood the Universe is a thorough, readable, and indispensable guide to the human species and how it operates.

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That’s human nature, the basic configuration of our species as a whole. What about human variation—the ways we differ from each other as individuals? Robert Plomin is the guy to ask, as he’s a giant in the field of behavioral genetics. He began his work in the 1970s, when the adoption- and twin-based studies that form the field’s foundation were just taking off.

The basic insights behind these studies are simple. Kids who are raised together share much of their environment; they generally are raised by the same adults, experience the same child care arrangements, enjoy the same material and health benefits from the household’s income, go to the same schools, and so on. Adopted siblings and twins, though, are unusual in how much of their genetic material they have in common. While traditional siblings and fraternal twins share about 50 percent of their genes, identical twins share virtually 100 percent and adopted siblings share none.

By looking to see how much these siblings resemble each other, we can suss out the relative contributions of genes, the “shared environment,” and other factors (including random chance, parts of the environment that kids raised together do not share, and simple measurement error). If adopted siblings were just as similar as biological siblings, or if identical twins were no more similar than fraternal twins, that would suggest that genes don’t matter. But if adopted siblings were no more similar than strangers, or if identical twins were exactly twice as similar as fraternal twins—mirroring the fact that they share twice as much DNA—that would suggest that genes are the only thing that make siblings alike.

When it comes to psychological traits such as intelligence, personality, and schizophrenia, the upshot is that the latter is closer to the truth: typically, about half of the “variance” is explained by genes, while far less of it, sometimes none, is explained by the shared environment. (The rest of it goes into that catch-all third bin.) This implies that the things we put so much effort into—parenting, schools, etc.—have relatively little impact, at least within the normal range. (No one is saying that severe abuse or deprivation won’t matter.) This has been known for decades, and formed the bedrock of Judith Rich Harris’s 1998 classic The Nurture Assumption.

Also long-established, if less widely discussed, is that even one’s environment is actually partly genetic: we actively shape our surroundings in ways that suit us. In one study, for instance, Plomin found that how much TV kids watch is partly genetic. In others, researchers have found a genetic component to the kinds of parenting that children receive. So research that, say, ties TV-watching and parenting styles to academic outcomes may in part be measuring kids’ genetics, not the effect of a bad family environment.

Over the last couple of decades, Plomin and other researchers have started to shift this research into the realm of DNA. The early results were not encouraging: even though the twin and adoption studies said that psychological traits were half-genetic or so, it was virtually impossible to find any genes that actually made a difference. It turns out that these traits are controlled by thousands of different genetic variants, each of which has only a minuscule effect. This means you need a huge study, with thousands and thousands of participants, to identify them statistically.

That’s expensive, but it’s happening, and it’s showing results. Plomin and others are finding boatloads of genes that affect important traits ranging from educational attainment to depression, with each variant explaining, on average, about 0.01 percent of the variance in the trait under study. And if you group a bunch of these genes together you can calculate a “polygenic score” for an individual—a number estimating his genetic endowment for that trait.

Since these traits are about half-genetic, such a score could in theory explain half the variance in them. So far, though, even the best ones top out around 10 percent. But that’s far from useless, so long as the scores are interpreted with care: they’re not prophecies, but they do highlight risks, including for mental illness. Someone with a bottom-tenth score for educational attainment, for example, has a 32 percent chance of going to college, versus 70 percent for someone in the top tenth. Plomin walks through some of his own polygenic scores, which help to explain how he became an eminent scientist despite growing up in a home with no books (he’s at the 94th percentile for educational attainment) and why he has to work to control his weight (he’s also at the 94th percentile for body mass index).

To learn all this at the hands of a man who helped to jumpstart this field, and who has pushed it forward into the modern era, ought to be a treat. To be blunt, however, Blueprint is not nearly as good as it could or should be. The writing gets just technical and clumsy enough that members of the general public may often have a hard time following it. Those better informed about the science, meanwhile, will learn little that’s new—and may notice a number of troubling errors in Plomin’s descriptions of basic statistical concepts, which I assume were the result of poor editing. (See especially the butchering of p-values, regression to the mean, and confidence intervals.)

At fewer than 200 pages (excluding the notes), it also doesn’t have room to address some highly relevant topics. These include epigenetics, the process by which genes are “expressed,” which some critics have presented as evidence of the environment’s power (as environmental factors can turn genes on or off). Also, a growing number of well-designed studies suggest that fairly normal changes to a child’s social environment—say, going to preschool, receiving food stamps, or moving to a different neighborhood—can have a sizable effect on his outcomes years later, a finding hard to square with decades’ worth of behavioral genetics claims that the “shared environment” is nearly toothless. It would have been nice to see these angles addressed.

So, this fascinating line of research still awaits a definitive explainer for the average reader.

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These two books are doubtlessly depressing to an extent. They suggest that in important ways, humanity’s efforts to change itself are doomed to fail. We’re simply not as malleable as we’d like. Neither the Left’s fantasies of extreme social engineering nor the Right’s prized equal opportunity will give everyone a fair shot at success.

But there are encouraging signs as well. Stewart-Williams’s writing on memes shows the power of ideas to change lives. And as Plomin notes, it’s not really clear why we should find the power of DNA any more problematic than we’d find an all-powerful environment.

One fascinating study showed that when the USSR ended and Estonia became a freer society, educational attainment and occupational status became more genetically heritable—because people were newly able to follow their own desires and reach their genetic potential. Would you rather be constrained by the situation you grew up in, or by your own abilities?  

Robert VerBruggen is a deputy managing editor of National Review.