Are some races smarter than others?

            On a smoggy January day I set out from the Indian capital, New Delhi, for the nearby state of Punjab to visit my extended family. It’s a journey I’ve taken many times before, usually napping my way past the lush farmland and fruit sellers flanking the highway, stopping only at a dhaba for a butter-soaked lunch before returning to sleep. But this time I stay awake to study the faces I pass while I’m on the road, to watch the bodies jostling through the traffic.

            I stare and I compare. The word “brown” doesn’t do any of us justice. Every possible skin color is represented: ebony, paper white, yellowish, and countless other shades, along with almost every possible feature. India is unique. The sheer size of the country and its environmental variety, from the sun-drenched beaches of the south to the snowy Himalayas of the north, seem to be paralleled by the physical diversity of its people.

            An encounter the same morning had made me look with fresh eyes at this place I thought I already knew. I’d met Sridhar Sivasubbu, a geneticist, in his scrupulously tidy office at the Institute of Genomics and Integrative Biology on Mathura Road in the heart of the city. Part of Sivasubbu’s work is to investigate human genetic variation within India, with the aim of battling rare diseases. In a nation of more than a billion, he told me, no rare genetic illness is actually all that unusual. With this many people, rarity becomes a relative concept. But what fascinates him more than that is the variety. India is a microcosm, an entire hemisphere represented inside one country.

            “We have something like fifty-five populations, major populations. Then there are minor populations within the country, and five linguistic groups are there,” he explained. Regions overlap genetically with other nations in South Asia and parts of the Middle East. The Andaman Islanders have genetic affinities to Aboriginal Australians. This breadth of difference may be one reason why today India is the only country left in the world to have its own government-funded Anthropological Survey, designed to study the biological and cultural variation of its citizens.

            But there’s also more to all this wondrous human diversity than meets the eye. One of the unsettling reasons that Indians exhibit such physical difference is that it’s partly self-imposed—the culture demands it. Many centuries of marriage within fiercely tight-knit communities and a caste system that stretches back perhaps two millennia to keep privileged and nonprivileged people apart, reinforced by the British under empire, have deliberately maintained the separation of populations.

            Romila Thapar has noted that there was always intermixing between groups in India, that the strict divisions today probably weren’t as strict in the past. But unlike neighboring China, which though larger than India is not quite so ethnically diverse, in India, freedom to marry and move between groups does seem to have been restrained. Millions prefer to marry within their own religion, color, caste, and community, however shallow a pool of potential partners that might leave them with. And their preferences are policed not by authorities enforcing laws but by families: cases of couples being attacked or killed for falling in love inappropriately occur on a regular basis. Intercaste marriage was legalized in 1954, yet a survey in 2016 found that as many as 40 percent of adults in Delhi who didn’t belong to the lowest castes thought there should still be laws preventing intercaste marriage.

            “You can find this in Hindus, you can find this in Christians, you can find this across India,” said Sivasubbu. “So it’s not about religion. It is about customs and marriage practices that have been passed down over generations. Indians tend to marry within the larger community that they live in, and in spite of all the few hundred years of knowledge that we have acquired, we still follow conservative and traditional marriage practices.”

            My mother grew up with these values. Although she ended up married to a man of a different caste, religion, and community, she nevertheless has a romantically fatalistic view of life, steered by a society that has forever told her that everything is circumscribed, that has for hundreds of years kept people in their place. For those raised this way, society’s hierarchies feel knitted into their bodies. Their faith in the power of heredity is so strong that it overwhelms how they think even about themselves. They find nothing odd in a dynasty that runs over multiple generations, be it political, artistic, or commercial. Some extol the virtues of caste as giving everyone a valued place in society, forgetting that for people consigned to a life of cleaning toilets, it’s little solace to be told that this is where they belong in the cosmic scheme of things.

            Parallels have been drawn with the British class system, or race in the United States, but caste has features of both and of neither. It is ugly in its own way. At birth, you inherit your place in this social hierarchy, and few transcend it. An “untouchable” at the bottom will be given society’s dirtiest work, existing in a permanent state of impurity, while those at the top of the ladder are a kind of aristocracy, favored for jobs and education (people I meet as a journalist still like to drop into conversation that they are Brahmins, the highest, priestly caste, expecting this to carry some weight). The distant origins of all this are likely to have been strategic in part, to keep wealth and property within families. Some castes tend to be congruent with certain trades, creating generations of teachers, merchants, or fisherman. Those at the peak are apparently supposed to show benevolence to those below, but in reality there is considerable discrimination and violence.

            Successive governments have brought in reservation policies, setting aside jobs and scholarships for disadvantaged castes. Even so, a report in 2014 by the international advocacy group Human Rights Watch found that teachers in some schools were still forcing lower-caste students to clean toilets and sit apart from everyone else. Top universities and colleges admit almost exclusively students of higher castes.

            When the Nobel Prize–winning geneticist James Watson compared Brahmins to Jews by claiming that both had been bred for academic excellence, he was using the language of both caste and science, seeing the two groups’ behavioral characteristics as genetic qualities passed down over centuries. Their fortune is believed to lie beyond circumstance, to be part of what they are. As a famous Indian economist belonging to a higher caste once told me, this is Indian culture, and it is unrealistic to expect change. It is taken as given that people are fundamentally different, that they are born a certain way. Everyone becomes trapped in the net of their ancestral history.

            So Sivasubbu’s comments overshadowed my thoughts as I traveled to Punjab. In India, skin color doesn’t always faithfully betray someone’s caste, but there’s a lingering view that being fairer is better, that it denotes a higher status. The four main caste groups are sometimes even designated by color—white, red, yellow and black—not unlike the way Europeans classified human races in the nineteenth century. “Somebody very tall or very fair-colored, obviously they would select an individual with similar features,” I had been told matter-of-factly by Indian population geneticist Kumarasamy Thangaraj. “So there is a selection operating, not by natural but by man-made selection.” I recall when I was flat hunting in Delhi before starting my first job there as a reporter, I was asked to list my skin shade on the rental form. Having only thought of myself as “brown” for most of my life, I had no idea what to write. The letting agent took a good look at me, and with a dirty smile scribbled, “Wheatish.” Color takes on a new subtlety when every degree of pigmentation matters.

            In both biological and social terms, then, India has long been a unique case study for scientists. This is why the race scientist and eugenicist Reginald Ruggles Gates was so captivated by the country. Here, systematic discrimination, the notion that groups of people are biologically pure and should be kept separate, that some populations are different from others, isn’t just an ideology. It’s a living practice.

            In the 1950s the Indian geneticist L. D. Sanghvi wrote that people in his country “are almost under an experimental environment . . . broken up into a large number of mutually exclusive groups, whose members are forbidden, by an inexorable social law, to marry outside their own group.”

            When the idea of race research became unpalatable after World War II, Sanghvi was one of the first to turn to population genetics. In India scientists like him could explore what happens when human groups stay “pure”—the kind of purity that nineteenth-century race scientists imagined might be possible, that Hitler wanted to see in Germany for the Nordic “master race,” and that white supremacists still want to see in parts of Europe and the United States. The grand social experiment that had already taken place in Indian society could reveal firsthand how the world would look if people mated only inside their narrow communities, whereby certain qualities and skills were selected for over many generations.

            What is remarkable is just how widely Indians today believe that caste is deeply, biologically meaningful, that it has created exactly what it must have been intended to create: a social order reflected in biology, with the smartest and most gifted at the top, and others in various professions with their own skills below, as warriors and merchants, or cleaners and servants. Even scientists think this way. “The caste system, whatever has been practiced for last several generations, or several thousands of years, has a definite impact on everything,” Thangaraj told me. Character traits and abilities get passed down over generations, he implied. “The offspring that’s coming out of that founder are going to have such character. Usually, then, they become very unique features of that particular population.”

            Sridhar Sivasubbu, too, suggested to me that people are biologically suited to the groups they are born into. By separating themselves for so long they had created genetic enclaves with particular talents, making caste not only a social reality but a biological one, too. “Clearly certain communities have certain biological abilities which they are born with. . . . We all look different and we each have our own strengths and abilities,” he said. For him, the differences are so profound that castes are analogous to separate races, as the population geneticist Luigi Luca Cavalli-Sforza might have defined them. “You could call two groups, two peoples, as completely different races and treat them as two separate entities. Or you could just celebrate both of them and say that they are different and each has the unique strength and weaknesses.”

            By way of an example, Sivasubbu pointed to Haryana, one of the states bordering New Delhi, which happens to be home to a disproportionate number of athletes, particularly wrestlers and runners. “So, clearly they seem to have a better physique in terms of strength,” he suggested. Another example he offered was that of several tribal communities, which he claimed were naturally gifted at archery.

            This casual speculation surprised me, coming as it did from a respectable geneticist. It showed that more than half a century of research into human variation hasn’t eliminated prejudice within science, wherever it’s done. Old stereotypes are still being projected onto people, but perhaps in new ways. In Haryana there is certainly a long cultural tradition of wrestling in some families, for which people train their whole lives. But lifelong training could just as easily explain the prevalence of athletes as any innate ability. And if tribal communities happen to contain more skilled archers, this is most probably because they have traditionally been the ones to use bows and arrows, developing their skills through sheer hours of practice.

            There’s a slippery slope here, assuming that everyone in a particular community should be limited to certain paths in life. Indeed, social categories like these were harnessed and promoted by the British during colonial rule. My father’s family, who were in the military and fought in both World Wars for the British Empire, were designated as one of the “martial races.” They were seen physically and morally as the perfect soldiers. My father became an engineer, his brother a headmaster. Few of his siblings followed the family tradition, and certainly none of the children. We are not all natural warriors.

            Yet I can’t help but ask myself whether Sivasubbu has a point. In 2018 scientists were amazed to discover that the nomadic Bajau people of Southeast Asia, who live almost entirely at sea, surviving by free-diving to hunt fish, had evolved an extraordinary ability to hold their breath underwater for long periods of time. The Bajau tend to have disproportionately larger spleens than nearby populations of farmers, which possibly helps them to keep up their blood oxygen levels when diving. There appears to be a measurable genetic difference between them and others, sharpened over many generations by living in an unusual environment.

            This raises a question we don’t like to ask out loud, but one that goes to the heart of the race debate. It is where race science began, with a belief that neglects history and jumps straight to the conclusion that the human zoo is like an animal zoo, each of us defined deep down by our stripes and spots. And it leads straight from the offensive observation made by James Watson on the preponderance of Jewish intellectuals and Indian Brahmins in academia. Might it be possible, as Watson implied, for a group of people, isolated enough by time, space, or culture, to adapt to their particular environment or circumstances in different ways? That they could evolve certain characteristics or abilities, that they might differ in their innate capacities?

            Wandering down this road may be of some scientific value, but it is also risky, I know, and it’s paved in blood. “Could there be psychological differences between population groups?” I asked Thangaraj, tentatively. I go further. “Differences in cognitive abilities?”

            “That kind of thing is not known yet,” he replied. “But I’m sure that everything has genetic basis.”

            Back in London, I’m on the train on my way to a leafy corner in the south of the city, Denmark Hill.

            The question of whether cognitive abilities, in the same way as skin color and height, have a genetic basis is one of the most controversial in human biology. It’s a grenade. And Robert Plomin is one of the few who has dared to handle it. A professor of behavioral genetics at the southern campus of King’s College London, he has dedicated his career to the search for the roots of intelligence, becoming one of the most divisive researchers in mainstream science. His work has far-reaching implications for how we think about human difference.

            Tall, with a smart white beard and a crisp, pale blue shirt, Plomin is disarmingly charming in person, and rarely says anything to me that doesn’t sound perfectly reasonable. I find him to be ruthlessly careful with his words. But there’s a message in his subtext. He moved to Britain from the United States in 1994, becoming known for brandishing the view that the cognitive differences between individuals can be accounted for largely in some way or another by genetics. The implication is that we are who we are, however we’re raised. But at the sharpest end, a few go so far as to take it to mean that the achievement gaps we see between population groups (or races, as some might call them) may also just lie in their DNA.

            It was in the 1970s, working at the University of Texas at Austin, that Plomin decided to dip his toe into the controversial field of behavioral genetics, eventually asking himself whether individual differences in intelligence might be heritable and to what degree. It was perilous scientific territory with enormous social implications.

            For him as a psychologist, he tells me, “It was still kind of forbidden to study genetics. It was dangerous professionally.” Part of the reason, of course, was the dark history of eugenics in the United States and Germany, which saw people sterilized or killed in the belief that they would pass on their “feeblemindedness” to their children. The handful who doggedly stuck with intelligence research after the war also tended to say inflammatory things. For example, in 1969 the American educational psychologist Arthur Jensen claimed that black Americans had substantially lower IQs than white Americans, and that IQ was also significantly heritable. This in turn suggested that the apparent black-white intelligence gap wasn’t because blacks were socioeconomically worse off or discriminated against. Plomin tells me he both personally knew and defended Jensen against his critics before he died.

            At the time, there was no genetic evidence to support Jensen. But Jensen predicted that scientists would one day discover such things as “intelligence genes,” which he believed would be “found in populations in different proportions, somewhat like the distribution of blood types.” To compare “intelligence genes” to blood types was telling because it was already known that blood types do vary in frequency between population groups. This would lead neatly to his next bit of speculation: that fewer of these “intelligence genes” would be present in the black population than in the white.

            Jensen’s work went on to feature prominently in The Bell Curve, the controversial 1994 book by Herrnstein and Murray. Herrnstein, a psychologist like Jensen, had long insisted that intelligence was heavily heritable, warning in 1971 that America was already slipping into a genetic caste system based on intelligence in which successful people were marrying each other and creating more successful children, while the unemployed languished because of their intellectual disadvantages, which “may run in the genes of a family just as certainly as bad teeth do now.” Parallels with India’s historic caste system were clear, except here it was being framed in purely biological terms. In his vision of the world, class, wealth, and race overlapped because of biology, not because of history.

            In the United States, much heat still surrounds the nation’s apparent black-white IQ gap. In 2006 the Canadian psychologist John Phillippe Rushton, who had been a pivotal figure in the Pioneer Fund and the Mankind Quarterly, published a brief commentary together with Arthur Jensen in the journal Psychological Science in which they repeated what they and Herrnstein had insisted their whole lives: that there was a racial gap of around fifteen IQ points and that the evidence it was innate was unassailable.

            As they knew, proving their hypothesis meant separating the effects of nature and nurture. This is the challenge that has dogged human biology for more than a century. How do we know that differences between people are genetic or innate in some other way, and not just the product of social and cultural factors? Every human being is a unique product of biology and environment, which makes answering this question almost impossible. Without being able to raise human genetic clones in a laboratory to run experiments on, the backbone of the psychological efforts therefore became twin studies. By observing the similarities between identical twins, researchers have for decades thought they might be able to discern whether certain traits might be more heritable than others. But twin studies, too, are tainted by a toxic past. Josef Mengele, the notorious Nazi doctor who trawled concentration camps for involuntary subjects, had picked out young twins to deliberately mutilate (via amputations) and dissect. He carried out on humans the kind of research that, for ethical reasons, is done only on flies. And scientists learned nothing from it except just how far into hell a person would go to get his results.

            For decades after the war, most researchers were wise to leave twins alone. In 1979 a psychologist at the University of Minnesota, Thomas Bouchard, reignited the flame. Studying a hundred pairs of twins who had been separated in infancy and then raised apart, he estimated that genetic factors accounted for approximately 70 percent of their variance in IQ, implying that the bulk of the differences we see between people who are healthy and well cared for are decided at birth. The rest lies in other factors in the environment, such as upbringing and schooling. Bouchard and his colleagues speculated that, at least in middle-class families living in industrialized societies, “although parents may be able to affect their children’s rate of cognitive skill acquisition, they may have relatively little influence on the ultimate level attained.” The implications of Bouchard’s work, which had been financed initially by the Pioneer Fund, were obvious. If some people weren’t doing so well at school—black American children, for example—it was nobody’s fault but their own genes’.

            At the time Bouchard was vilified, picketed, and called a racist. Many decades have passed since then, but in some ways Robert Plomin has inherited this tarnished mantle. He has become part of the push to rehabilitate intelligence research, running his own studies using twin and sibling data to understand inheritance. The key is to see, as Bouchard did, whether twins raised in separate environments end up the same. And he believes that, more or less, they do.

            “Everything is heritable,” Plomin tells me straight out.

            “In fact, I am not aware of anything reliably measured that’s been shown not to be heritable in terms of psychology. . . . Everything is moderately heritable.” Using studies of twins—particularly those who have been adopted into different families—his estimate for the portion of intelligence that is heritable is around 50 percent, which may be far lower than the figure Bouchard came up with, but is still pretty high. If half of our intelligence can be decided by our genes, then a large part of academic achievement may well be innate, immutable.

            There are some important caveats, however. First, measurement of intelligence is itself fraught with pitfalls—nobody is fully satisfied that any IQ test can really do the job. Second, rates of heritability aren’t the same for everyone. They depend critically on the environments of the people you’re studying. Take a packet of seeds and shake half of them into a container filled with nutrient-rich soil, blessed with all the water and sunshine they need. Take the other half and put them in a container of poor soil with little water and light. In both pots, individual plants will grow to various heights, some taller, some smaller. The differences you see within each pot are highly hereditary because their conditions are the same. But in the first pot, each seed has been given the full opportunity to achieve its potential. In the second container, they haven’t been, so the plants in this second pot will inevitably look smaller and scrappier. In this weaker one, even the naturally strongest seed may not reach the same height as many of the plants in the more fortunate container. So the differences between the pots are not attributable to heredity.

            Some traits, such as hair color, are very strongly determined genetically. Hair color doesn’t change depending on the environment, unless perhaps that environment is a hair salon. Even skin color is to some extent affected by how we live. A group of paler-skinned children who play out in the sun all day will temporarily end up with darker pigmentation than paler children who don’t, but this difference is purely due to environmental factors. So when scientists say that a trait such as height or intelligence is partly heritable, the only way they can know how much is by looking at people in the same normal, healthy environments, with few differences in how they are raised or treated by society. If some of the people are deprived, it can obscure the genetic influence.

            For instance, studies have shown that although the two Korean populations were until recently the same, today, North Koreans are on average a little shorter than South Koreans. An alien landing on our planet with no knowledge of their histories might call it a racial difference, but it is purely down to their dramatically different economic circumstances. Height has very high heritability, but South Koreans have been prosperous and well fed and North Koreans haven’t, so the difference in height between them today is not genetic at all.

            The problem with studies of adopted twins, as critics have noted, is that they usually involve children of fairly comfortable socioeconomic means. Even if the children are raised apart, they’re still not at the poorest end of society, where good nutrition and a stable home life can be factors in their upbringing. They tend to go to fairly good schools. There’s a risk, then, that these studies underestimate the role of environment across the true range of how people live.

            But let’s just assume for now that Robert Plomin and his twin studies are reliable, and that IQ tests are a fairly good measure of what we know as intelligence. Even if intelligence is at least half heritable among children raised under normal conditions, scientists like Plomin must also be able to point to the genes responsible for the effects they claim to see. They need to be able to explain, step by step, how they get from this twin correlation to the genes and then to the brain. To date, they haven’t found anywhere near all the genes involved. In 2017 Plomin, along with a battalion of researchers in the Netherlands, Sweden, and the United States, published the results of a study of nearly eighty thousand people, which claimed to have found forty new genes linked to intelligence, bringing the known total to have such an effect to fifty-two. It was announced in the press as a breakthrough, but in reality these genes represented just a drop in the ocean. There are many, many more. “We’re not talking about a handful of genes, we’re talking about thousands of genes of very small effect,” he admits. Half a century and millions of research dollars on, Arthur Jensen’s prediction remains stubbornly unfulfilled.

            Despite being unable to definitively isolate intelligence in human DNA, Plomin is proud of what he’s achieved so far. He believes he is getting closer to an answer. “Do you know, two years ago we could explain 1 percent of the variance in intelligence with DNA? Now we can explain 10 percent! And it’s only getting bigger. I would be amazed if at the end of the year we’re not explaining 15 percent.” Supposing he does, though, he would still be left with the challenge of finding a single mechanism, even one biological pathway, explaining how any of these genetic variations acts on the brain and leads to what we see as someone’s general intelligence. We know, for instance, that X-linked mental retardation is a genetic condition, identifiable in a person’s DNA, reliably leading to certain intellectual disabilities. There’s a quantifiable link between the gene, inheritance, and cognition. But for everyday intelligence, scientists don’t have anything clear like this.

            Eric Turkheimer, a psychologist at the University of Virginia, believes they will never find it. “I’ve been around for a while,” he tells me. “I’ve been in this field thirty years, and every single one of those thirty years, the biology people of one stripe or another have been saying, ‘I know we’re not there yet but in five years, as soon as this next piece of technology is nailed, as soon as we have brain scans, as soon as the genome project is completed . . .’ It’s always right around the corner. And the reason I don’t believe it is because I don’t believe that’s the way genetic causation works.”

            Turkheimer compares intelligence to marriage. Psychologists know that if you have an identical twin who has been divorced, statistically you are more likely to be divorced yourself. There is no suggestion that there’s such a thing as a gene for divorce, because people understand this to be a complex outcome, influenced by countless factors, including social and personality factors. “I think there are limits to how much we can understand something as complicated as divorce looking from the bottom up,” Turkheimer says.

            When it comes to intelligence, like most other complex traits, heritability depends crucially on context. He and his colleagues have seen, for instance, that in studies of people with the lowest socioeconomic status, environment explains almost all the variation researchers see in IQ, with genes accounting for practically nothing. Children who are the most socially and economically disadvantaged have been shown to lose IQ points over their summer holidays, while the most advantaged ones gain knowledge and skills over the same time period.

            So for Turkheimer, it beggars belief that anyone should assume that the cognitive gaps psychologists now claim to see between racial groups in the United States could be biological. The effects of slavery and centuries of racism, in all its forms, are hard to quantify, but black Americans have undoubtedly suffered in ways that have left their marks on generations. “Millions of people were kidnapped and thrown in the bottom of boats and taken across the ocean, and a third of them died on the trip, and then thrown on plantations and enslaved for hundreds of years. And after that, treated with total discrimination. And now, now their IQs are a little lower? And we’re saying it’s in their genes? My feeling about that is, give me a break.”

            We know from the seeds-planted-in-two-pots example that you can’t compare populations that live in different environments because the differences between them could easily be ascribed to nurture rather than nature. And there is no doubt that the social and economic circumstances of most black Americans remain significantly behind those of white Americans. The Institute for Women’s Policy Research in Washington, DC, found that in 2017 the median weekly wage taken home by a white man working full-time was 33 percent higher than that taken home by a black man in a comparable job. It was almost 50 percent higher than that of a black woman. The wealth gap—“wealth” refers to assets accumulated over generations—is even starker. Research in 2017 showed that of lower- and middle-income households, white families have four times as much wealth as black families. According to the most recent data, two-thirds of black children live in single-parent families, compared with a quarter of children in “non-Hispanic” white families. Across the board, black Americans are significantly worse off, from the level of police brutality they suffer to the quality of healthcare and schooling they receive.

            The logical consequence of insisting that IQ gaps between races are biologically determined is that nothing in human society can really be changed. In an age in which some like to believe that we have transcended the old rules of social inequality, when the playing field is supposed to be level, when women have the vote, when black Americans have civil rights, and colonialism is dead, they believe that biology is all that’s left to explain the disparity that remains. Inequality, then, must be natural, the product of the survival of the fittest. Yet we still don’t have the genetic evidence to prove any of this, says Turkheimer. All we have is the belief that the proof will be there somewhere in the genes.

            “I don’t see how we can get from where we are now to that kind of racial speculating that people like to do.”

            Turkheimer lives in Charlottesville, Virginia. In August 2017 the city became the infamous backdrop to a Unite the Right rally that drew together white nationalists, fascists, and neo-Nazis from across the United States, brandishing swastikas and Confederate flags. Their march eventually escalated into violence, culminating in the death of a peaceful antiracism protestor, Heather Heyer, who was struck when a car drove into her and others who had braved the threat of violence to challenge the message of those on the far-right. It was a day that was described by many as a wake-up call to America. The dream of a postracial society seemed more distant than ever.

            “The synagogue we belong to is right next to the park where it all happened,” recalls Turkheimer. A letter from his rabbi told a disturbing story. “It was Saturday morning, so there were services inside. They locked the doors while people marched up and down the street yelling, ‘Burn it down.’”

            In the following days, editors of the scientific journal Nature felt the need to run an editorial reaffirming that science cannot and should not be used to justify prejudice. It was a brief but remarkable statement, proving just how potent scientific racism was seen to have become. “This is not a new phenomenon,” the editors remarked about Charlottesville. “But the recent worldwide rise of populist politics is again empowering disturbing opinions about gender and racial differences that seek to misuse science to reduce the status of both groups and individuals in a systematic way.”

            Turkheimer explains that the problem is not in the data, which is so far either unclear or unsupportive of racist interpretations of intelligence, but in the rampant speculation. If science could conclusively tell us that there was a biological difference in our DNA that made some groups smarter than others, there would be no more need for debate. “But my point is, I don’t think we have that. And so what we’re doing instead is speculating about our intuitions, speculating about people’s dumb intuitions about Jews and blacks and whoever it is people like to speculate about.”

            If bad intuition is the problem, it’s a problem we all have. Intelligence is just as multifaceted a cognitive trait as any other, but there’s a widespread assumption that it is very heavily influenced by inherited natural ability. In reality, parents’ IQ scores can only explain 15 percent of the variance in their own children, admits Plomin. Exceptionally smart parents are likely to have children a little less smart than themselves because of a phenomenon known as regression to the mean, which works to bring everyone in a population back closer to the average. Very bright children are likelier to emerge from parents in the middle of the intelligence range, where most people live. This was precisely the statistical fact that made eugenics impossible.

            As the Nature editorial noted, “Every individual is a potential exception.” Plomin himself is living evidence of just how possible it is for individuals to be unlike the rest of their family members. He was raised in a working-class family in Chicago, and neither of his parents went to college. “My sister is as different from me as you can be, in looks, in personality, and she was never interested in books. I would go to the library and get all these books, and she didn’t go to university,” he tells me.

            Today, there remains little doubt that there is at least some heritable component to what we perceive to be an individual’s ability to reason and solve problems, to process complex ideas and generally figure things out. But it’s the degree of flexibility in there, in this hard-to-pin-down thing we call intelligence, that still eats away at some in the scientific community, not to mention many on the outside who are interested in the politics of it all. The debate is continually reduced to a simple question of nature and nurture, to biology and the environment.

            But it’s not such a simple equation. Even identical twins can sometimes show very different abilities. In Thomas Bouchard’s twin studies, he came across a pair of brothers who were raised in wildly different environments. One grew up to be an uneducated manual laborer and the other was highly educated. An IQ difference of twenty-four points separated them. In the normal course of development, “a ten- or twelve-point difference between identical twins is not unusual,” Turkheimer tells me.

            “So how much flexibility might there be in the system?”

            In 1984 James Flynn, an intelligence researcher based at the University of Otago in New Zealand, raised a collective gasp in the scientific community when he announced that for nearly fifty years, since 1932, American IQs had been rising at a rate of about three points a decade. This finding could have been interpreted as people getting significantly smarter with each passing generation. In reality, as Flynn recognized, people had simply become much more skilled at taking IQ tests. This phenomenon is now known as the “Flynn effect.”

            Test takers were performing better not because they had evolved mental capacities beyond those of their grandparents but because their minds were being nurtured and sharpened now in ways they weren’t before, by better and more education, more intellectually demanding jobs and hobbies. “The period in question shows the radical malleability of IQ during a time of normal environmental change,” Flynn wrote at the end of his paper. Whatever link to intelligence is measured by IQ tests, it saw a benefit from the passage of time, from cultural change.

            Comparing countries, Flynn saw similar effects everywhere. Different versions of IQ tests are used across the world, with varying results. But between 1951 and 1975 Japan saw an IQ gain of more than twenty points. In Britain it was almost eight points between 1938 and 1979. Countries that were fully modern before the testing period began tended to show more modest gains than those that underwent significant social and economic change. Kenya and Caribbean nations made particularly big leaps. Scandinavian countries, on the other hand, showed a peak and then arguably even a little decline. Flynn proved that there must be a great deal of flexibility in intelligence.

            Mankind Quarterly editor Gerhard Meisenberg had told me that some countries are too cognitively challenged to prosper, that essentially they are poor because they are stupid. His only evidence was historical IQ test scores. Should anyone need it, the Flynn effect is some of the best proof yet that he is wrong. It shows that environment matters in IQ test results, even at a population level. In a paper published in American Psychologist in 2012, Flynn, Turkheimer and other experts suggested that, at this rate, the apparent “IQ gap between developing and developed countries could close by the end of the 21st century.” Flynn has shown that the IQ performance of African Americans has risen faster than that of white Americans in the same time period. Between 1972 and 2002 they gained between seven and ten IQ points on “non-Hispanic whites.”

            Another easily overlooked fact in the American black-white IQ gap debate is that very few African Americans are quite as ancestrally African as we might think. In 1976 sociologist Robert Stuckert used US Census data to estimate that as many as a 25 percent of people listed as white might reasonably have some African ancestors, and as many as 80 percent of black Americans were likely to have some non-African ancestors. In 2015 geneticists at Harvard University and researchers from the ancestry-testing company 23andMe investigated the backgrounds of more than five thousand people who self-identified as African Americans, and found that on average almost a quarter of their ancestry was European.

            This should come as little surprise. The sexual exploitation of black women by their white owners was common during slavery. Thomas Jefferson is thought to have fathered children by a slave in his household, Sally Hemings, who was herself of mixed ancestry. And then, in the last century the United States has become ever more interwoven as the barriers between interracial relationships and marriage have been beaten down. Historically the “one-drop rule” meant that anyone with even the smallest degree of African ancestry—one drop of blood—was classified as black. Today, people who look at all “black,” however complicated their heritage, are treated socially as black.

            But if the biological portion of intelligence is rooted in a complex mixture of many thousands of genes, as biologists now agree it is, then it stands to reason that someone of mixed ancestry will have a mix of intelligence-linked genes from most if not all of their recent forebears. They wouldn’t inherit genes from those with just one skin shade and not another. And if that’s the case, and there are indeed innate, genetic racial differences in intelligence, then logic dictates that they should show up in people of mixed ancestry. If, as Rushton and Jensen implied, black people are biologically less smart, then shouldn’t black Americans with higher proportions of white European ancestry have slightly higher IQs?

            As far back as 1936, a study of exactly this kind was published by two American schoolteachers, Paul Witty and Martin Jenkins. They picked sixty-three of the highest-performing black children in the Chicago public school system, and compared their IQs with the proportion of white ancestry they were thought to have, according to information provided by their parents. The results revealed no gap at all. Having more white ancestry didn’t raise a child’s IQ. Indeed, the most remarkable student in the group, a girl with an IQ of 200, was reported to have no white ancestry whatsoever.

            A similar study was carried out much later, in 1986, this time looking at black children who had been adopted into middle-class black and white families. Children who had one white parent and one black had around the same IQs as children with two black parents. What did make a difference in performance, though, was the family they were adopted into. The black and mixed-ancestry children adopted into white families had IQs thirteen points higher than those adopted into black families.

            Andrew Colman, a psychologist originally from South Africa who now works at the University of Leicester in the UK, has interrogated the claims made by scientists who insist that intelligence gaps between races are real. He believes that research like this strongly indicates that environmental factors could well account for the entire black-white IQ gap in the United States. Even for those who claim to show contradictory evidence, he writes, “It is literally impossible to raise Black, White and mixed-race children in identical environments if racism itself is a significant environmental factor.” Being in the same school or even in the same family means little if society as a whole sees you as substandard. Colman accuses researchers who cling to the idea that “negroes show some degree of genetic inferiority,” as one once wrote, of a form of “self abuse.”

            It is interesting how the debate over racial differences in IQ takes on a different flavor in other countries. The United States seems to be a special case. In the United Kingdom, the group of sixteen-year-olds that achieves the lowest grades in IQ tests is white working-class boys, followed by white working-class girls. Yet scientists haven’t leaped up to claim that low intelligence is rooted in whiteness. There’s no evidence that being white in the UK is a socially disadvantaging factor either, so by this logic it must be their socioeconomic status that’s the problem. In the decade to from 2006 to 2016, some of the greatest progress in educational attainment in the UK was seen among Bangladeshi, black African, and Chinese pupils. Girls have also historically tended to outperform boys, even though there is no average intelligence gap between the sexes. According to the founder of the Sutton Trust, which researches social mobility in the UK, it’s clear that culture is at play here. There are social influences where class, ethnicity, and gender intersect, and they all affect achievement.

            This is a point that even Robert Plomin—whose work has been described in Nature as “vintage genetic determinism”—concedes. He acknowledges that studying group differences in intelligence is fraught because it is impossible to control adequately for the environmental effects, adding that he doesn’t see any value in studying racial differences in intelligence. “Based on what we know now, I don’t see how you would do it. Certainly for black-white differences, people have tried for a very long time and I don’t think we’re any further along,” he tells me. “We’ve had forty years of history of this, and it’s just a lot of heat and no light.”

            Heritability does matter, he insists before I leave his office. This position is, after all, his bread and butter. But he surprises me by adding that if you measure individual differences and find some people are a lot better than others, “they all can achieve incredible levels of skill given culture.”

            Sridhar Sivasubbu looked at me from behind his thick brush of a mustache.

            I had asked him about his own community and what it meant to him. He told me that he came from a particular Tamil group in southern India known in ancient times for being warriors, whose members nowadays tend to join the military or the police force. “If you go back and read the history of my own community, largely people have been doing this for ages, so people just keep doing it. That’s what they learned.” As a scientist, he happened to be an outlier. I couldn’t help but detect a hint of shame in his voice, or perhaps it was just regret, for the well-trodden path he chose not to take.

            “People tend to follow what their ancestors did,” he mused. In a country where roots go so far back in time that truth and myth are almost the same thing, connections to the past are not easily severed. They define how people live, forming the rigid framework of a sometimes precarious existence. “Let’s say we go back a few hundred years. You still had a set of beliefs, you still had a set of skills, trades that would be passed in the community. So you learned it, and you used that for livelihood. There will be communities that will end up growing a certain type of crop, in a certain type of region,” he explained. “It helped them survive. You also had the bonding, friends, family, neighbors. So it helped you in times of crisis.”

            But keeping close to a group has its costs. India’s long history of community marriage has certainly left a mark in the genetic profiles of its inhabitants. These marks are most obvious when it comes to health. “A genetic disease tends to remain in the community,” Sivasubbu told me. Studying particularly isolated communities has revealed stagnant pools. For the very smallest populations, reluctance to marry outside the group can be deadly. The Parsis, descended from Persians who moved to India more than a thousand years ago, suffer such high rates of particular forms of breast and prostate cancer, possibly inherited, that there have been fears the group may disappear altogether.

            Sivasubbu has helped identify other Indian families with rare genetic illnesses, including one that left siblings covered in dried skin resembling the scales on a snake, and another that is a neurological disorder so severe that the parents wanted their children euthanized. These illnesses emerged for the simple reason that their communities were too close-knit. People would end up unwittingly married to someone with a common recent ancestor, and if they happened to share the same recessive genes for a rare disease, the disease was more likely to occur in their children. The same dynamic can be seen with Tay-Sachs, a genetic nerve disorder that is more common than average among Ashkenazi Jews and non-Jewish French Canadians living near the Saint Lawrence River. By isolating themselves, populations have formed tight bonds, but the smaller groups have also burdened themselves with higher genetic risks. Racial “purity” comes with a high price.

            I asked Sivasubbu whether he had married within his own community or had chosen to abandon that practice, knowing the risks. He told me that, despite fully understanding the genetic problems, his culture was so important to him that he found a wife from within his group. So long as he followed certain rules around choosing someone not too closely related to him, he believed it was better to stay tight to his community than to leave it. “It was a very conscious decision, very conscious decision. It’s going back to your roots, your beliefs,” he said, smiling.

            For me, as a person of Indian ancestry raised in London, between two cultures but somewhat detached from both, this was something I had never fully understood. In that moment it struck me just how powerful a thing culture can be. It can make us act against our better judgment, but it also anchors us in the world, in time and in place. Culture, and the safety and security it brings, can have such a profound impact on behavior over generations, that to outsiders the cause of the behavior may well appear to be genetic. It can seem to be woven into a person, unshakable, when in fact that same individual under other circumstances and raised in another place may behave completely differently.

            When we see the effects of culture, we can’t help but dream up biological mechanisms to explain it. The newly discovered travel diaries of Albert Einstein, written around 1922, have revealed that even he formed generalizations as he toured the world, despite being an antiracist humanitarian. He described the Chinese as an “industrious, filthy, obtuse people,” adding, “It would be a pity if these Chinese supplant all other races.” Perhaps he imagined, like the builders of the old human zoos, that our differences run all the way from our habits into our bones, that to know one Chinese person is to know them all.

            Biologists Marcus Feldman at Stanford University and Sohini Ramachandran at Brown University have suggested that the “missing heritability” that scientists have for so long struggled to find in our DNA when it comes to intelligence and other complex traits may in fact be explained by the magic ingredient of culture. New scientific tools help us understand our genomes better, but they have only reduced the proportion of intelligence scientists now believe to be heritable. Feldman and Ramachandran ask the obvious: Why do scientists not look elsewhere for explanations?

            In the same way that our parents pass on their genes to us, they also pass on their culture, their habits, their ways of thinking and doing things. And this can happen over generations. It is so sticky and persistent that it may well look biological to an observer. This is why measuring differences between groups, even over long periods of time, is laden with error. We are social beings, not just biological ones.

            “The evolution of the Indian caste system is the perfect example of social determinism,” an Indian biologist, Rama Shankar Singh, wrote in 2001. Studying the biological differences between castes, Singh started to understand it as a system defined not by evolved differences that made people better at different things, but as a set of barriers maintained by society for so long that they felt like they were in the blood. Lives and choices were constrained by the invisible forces of culture, and so everything remained stratified. Everyone kept their position for fear of stepping out. We don’t change easily.

            But we can change. As societies do shift and inequalities finally flatten, then we start to see our assumptions overturned. Stepping out of a rigid, unjust system can prove just how flexible we really are, just how far outside our genes our differences really may lie. In April 2018 a study was published that looked into the performance of Indian bureaucrats hired as result of affirmative action policies. The Indian Administrative Service, one of the largest and most powerful bureaucracies in the world, is also one of the toughest places to land a job. Of the 400,000 people who apply, 7,500 are invited to take a grueling exam, of which as few as 100 or so will be offered a position. Controversially, half of these vacancies are then reserved for marginalized castes, whose slightly lower scores would usually disqualify them.

            A common assumption has been that, even though they help redress social inequality, these quotas must have an impact on standards. If people have to be given a leg up to get in, then they surely can’t be as good? Some believe that those born into lower castes are innately incapable of doing these high-status jobs well anyway, regardless of their actual socioeconomic position. But when they investigated one particularly large sample project, American scholars Rikhil Bhavnani and Alexander Lee found no statistically significant difference in performance at all. “Improvements in diversity can be obtained without efficiency losses,” they concluded. Caste made no impact.

            Indeed, the lower-caste applicants who got through the usual way, without the quota, tended to perform somewhat better than average.