This article was published in Scientific American’s former blog network and reflects the views of the author, not necessarily those of Scientific American
Back in the 1970s, nurture ruled the intellectual world and sex, not just gender, was thought to be entirely socially constructed. Oh, to be back in an era when everything was so malleable. Just imagine the possibilities of how we could mold our children (and society). As recently as 2000, the year the Human Genome Project draft sequence was completed, the late Harvard biologist Stephen J. Gould wrote, “There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain”
Today, however, we now know that much of human behavior and social life is genetically influenced and not entirely programmable by social inputs. Further, we now know that natural selection has continued apace and perhaps even sped up over the last 10,000 years since we settled down as farmers. Counterintuitively, this does not mean we have no influence on the future of the human race. Rather, now that we have mapped the genetic architecture behind a wide range of outcomes—from height to cognitive ability—a brave new world has opened up whereby we can select our mates, and, yes, even our children, by and for their genotypes.
Heritability—the proportion of variation in a trait within a population that is explained by genetic differences—ranges from about one-third for religiousness to about three-quarters for IQ, with personality, education level and even income falling somewhere in the middle. Genetic influence on human behavior is so pervasive that it has led the psychologist Eric Turkheimer to coin the “first law of behavior genetics”: All human behavioral traits are heritable. (His second law goes further in arguing that: The effect of being raised in the same family is smaller than the effect of genes.)
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For most of the history of research on human behavior, the influence of nature and nurture has been assessed by studying twins or adoptees or other kin. These approaches have proved to converge on results that are robust to the assumptions of particular models. But their big limitation has been that they can only infer the relative contributions of genes and environment as if they were measuring the mass of elephants by measuring the shadows they cast.
The recent mapping of the human genome has changed all that. Since the day in 2000 when President Clinton announced that the book of life had been decoded, the price of genotyping a person’s DNA has been plummeting. Today, for about $100, anyone can receive a million bits of information about their own genetic makeup from a company like 23andme or Ancestry.com. Free online apps allow one to augment these data up to about 3 million markers. These data have changed the game for social and behavioral scientists and will soon affect how we all live our lives.
Most social scientists avoid genetics like it’s a communicable disease, but a growing number of us have dived into this new and growing pool of data. We have found genetic markers for depression, for fertility and for educational performance. Most importantly, by summing the results across all twenty-three pairs of chromosomes, we can calculate for each individual a unique number that represents his/her genetic potential for that trait.
To take educational attainment as an example: Someone who is at the 10th percentile in his genetic score is predicted to graduate high school and stop there. But someone at the 90th percentile is likely to get more than two whole years of additional schooling—independent of environment. Today these polygenic scores—as they are called—are noisy predictors. But rapid progress is being made such that soon a bit of saliva or blood from a newborn will be able to capture her full genetic potential for educational attainment—along with her genetically predicted height, body mass index and cardiovascular risk.
For social scientists, policy makers, educators and even medical professionals, the promise is to use these polygenic scores to factor out genes when we want to study the environment—say, the impact of good versus bad teachers, parental divorce, family income, and so on. A bonus is that we can see how environmental influences differentially ripple through the population producing individual differences based on genotype. For example, why do some soldiers get PTSD when exposed to combat while others are not affected? Why do some children wilt in the face of poverty and social disorganization while others are relatively unaffected by their family’s economic circumstances? The intuition is that nature and nurture interact to produce the variegated field of wildflowers we call the human population.
This interplay between nature and nurture is part of the reason why—despite the fact that genetically endowed people (i.e. who have high PGSs) tend to marry each other—we have not yet emerged into a “genotocracy,” that is, a genetically-based caste-like hierarchical society. A second factor is that while there is a modest tendency for the genetically endowed to reproduce with similarly lucky people, there’s lots of error in our attempts to sort. Additionally, genetic differences tend to have outsized effects within families, acting as an engine of social mobility.
What I mean by this is that if we compare the education levels of two random people in the population who differ by, say 30 percent, on their polygenic scores, the high scorer is, on average, likely to have completed a half a grade more schooling. But if we compare two brothers or sisters with the same absolute difference in their genetic scores, the difference in their schooling is likely to be more than a half a grade. The family as a cauldron of invidious comparisons and labelling accentuates rather than mitigates genetic differences. Finally, of course, environment matters at least as much as genes do. But we should not take solace in the fact that the effects of family environment on economic success are significant. A situation where a child with the genetic potential to be a mathematician is thwarted due to being born into a socially disadvantaged family is no fairer than the genetically-determined world and less efficient for society as a whole, to boot.
We still have a long way to go to understand the road from DNA to complex outcomes—be that IQ or even height or diabetes. To take the case of intelligence, there is no doubt that much of the genetic variation that contributes to measurable outcomes works via central nervous system development. But it is just as probable that some of the genetic effect works through, say, physical attractiveness, given the psychological studies that show kids rated as attractive get more positive, verbal attention than their less visually appealing counterparts. That is to say: Just because something is genetic does not mean that it is legitimate or efficient for society.
Even if we eliminated the nefarious influence of unequal environments altogether, we would still need social scientists to unpack the ways that our genes affect our success in life to make sure the mechanisms by which genes determined success were fair—i.e. worked through factors that contributed to the common good and not, say, through discrimination based on physical features like skin tone. Equally important is the recognition that just because we find that a given outcome is largely genetic in origin, it does not mean we cannot do anything about it. Take the case of myopia, a trait that is highly influenced by our genetic makeup. Last time I checked, glasses worked for almost everyone who has suffered from it.
The fact that we don’t know the biological or social pathways by which our polygenic scores influence us does not mean that many folks will wait to act on the torrent of genetic information and findings that are pouring in. With consumer genomics growing year by year—at last count the service 23andme had over one and a quarter million subscribers—the data are already there for enterprising Americans to say, calculate their genetic scores on a variety of outcomes from dementia risk to verbal ability and upload them to their online dating profiles. We might not care about the genomes of those we hook up with, but when we get serious, privileged people who have access to these sorts of data might want to screen out genetically disadvantaged suitors who might pass on bad alleles to their offspring.
And given ongoing trends toward later and later ages at which women in the US and Europe are giving birth, and the corresponding adoption of IVF among those who can afford it, soon parents who can afford to will not only be testing their embryos for single gene diseases like Huntington’s or Tay-Sachs, but may also be choosing which embryo to implant based on the predicted IQ, height, or athletic ability of their little frozen blastulae. “It’s still you,” to quote the genetic counselor in the prescient 1997 movie, GATTACA, “It’s just the best of you.”
Much recent attention has been given to novel gene editing technology, CRISPR, which may soon eliminate single-gene diseases. But since traits like math ability and impulse control that most parents care about are spread across thousands of little effects in the genome, selective mating and embryo screening is likely to play a much larger role in how we artificially select future generations. We will have human Genetically Selected Organisms before we have GMO humans.
This revolution is coming, whether bioethicists like it or not. In China, for example, where there is much less squeamishness about “playing God” than there is in the Judeo-Christian West, there are already large scale efforts underway to find the genetic code for high IQ. And if we ban selective screening here, potential parents with the means will merely fly to Singapore. The social consequences of such developments are enormous. We may not be living in a genotocracy in the present day—despite what Charles Murray and Richard Herrnstein tried to claim two decades ago in The Bell Curve—but before long the wall between social and natural inequality may totally collapse. Who knows what kind of world will follow?