The Fear of Bias Is Itself a Bias — And Neither Side Owns the Evidence

The orthodoxy maintains that the average genetic differences among people grouped according to today’s racial terms are so trivial when it comes to any meaningful biological traits that those differences can be ignored. The orthodoxy goes further, holding that we should be anxious about any research into genetic differences among populations. The concern is that such research, no matter how well-intentioned, is located on a slippery slope that leads to the kinds of pseudoscientific arguments about biological difference that were used in the past to try to justify the slave trade, the eugenics movement and the Nazis’ murder of six million Jews. I have deep sympathy for the concern that genetic discoveries could be misused to justify racism. But as a geneticist I also know that it is simply no longer possible to ignore average genetic differences among “races.”

Ancient DNA has transformed our understanding of population history, but its potential to reveal as much about human evolutionary biology has not been realized because of limited sample sizes and the difficulty of distinguishing sustained rises in allele frequency increasing fitness—directional selection—from shifts due to migrations, population structure, or non-adaptive purifying or stabilizing selection. Here we present a method for detecting directional selection in ancient DNA time-series data that tests for consistent trends in allele frequency change over time, and apply it to 15,836 West Eurasians (10,016 with new data). Previous work has shown that classic hard sweeps driving advantageous mutations to fixation have been rare over the broad span of human evolution8,9. By contrast, in the past ten millennia, we find that many hundreds of alleles have been affected by strong directional selection. We also document one-standard-deviation changes on the scale of modern variation in combinations of alleles that today predict complex traits. This includes decreases in predicted body fat and schizophrenia, and increases in measures of cognitive performance. These effects were measured in industrialized societies, and it remains unclear how these relate to phenotypes that were adaptive in the past. We estimate selection coefficients at 9.7 million variants, enabling study of how Darwinian forces couple to allelic effects and shape the genetic architecture of complex traits.

The past 30 years of research in intelligence has produced a wealth of knowledge about the causes and consequences of differences in intelligence between individuals, and today mainstream opinion is that individual differences in intelligence are caused by both genetic and environmental influences. Much more contentious is the discussion over the cause of mean intelligence differences between racial or ethnic groups. In contrast to the general consensus that interindividual differences are both genetic and environmental in origin, some claim that mean intelligence differences between racial groups are completely environmental in origin, whereas others postulate a mix of genetic and environmental causes. In this article I discuss 5 lines of research that provide evidence that mean differences in intelligence between racial and ethnic groups are partially genetic. These lines of evidence are findings in support of Spearman’s hypothesis, consistent results from tests of measurement invariance across American racial groups, the mathematical relationship that exists for between-group and within-group sources of heritability, genomic data derived from genome-wide association studies of intelligence and polygenic scores applied to diverse samples, and admixture studies. I also discuss future potential lines of evidence regarding the causes of average group differences across racial groups. However, the data are not fully conclusive, and the exact degree to which genes influence intergroup mean differences in intelligence is not known. This discussion applies only to native English speakers born in the United States and not necessarily to any other human populations.

Many scholars have criticized The Mismeasure of Man periodically throughout its 38-year history. For example, James T. Sanders stated that Gould’s attempt to link his argument to anti-racism was a ploy to smear intelligence scholars and Gould’s enemies as evil people. Arthur Jensen argued in 1982 that Gould misrepresented Jensen’s ideas and often demolished strawmen that no intelligence scholar believes, including the boogeyman of “biological determinism.” John Carroll showed that Gould understood neither the purpose nor interpretation of factor analysis (a statistical procedure often used to evaluate data from psychological tests) and that Gould’s attacks on factor analysis do nothing to alter the importance of intelligence tests, nor the mass of evidence—impossible to dispute—that they predict real-life outcomes. Most criticism of The Mismeasure of Man was confined to the recherché world of psychologists who study intelligence. However, a new debate opened up in 2011 when a team of anthropologists argued that Gould’s analysis of the data on cranium measurements from 19th century scientist Samuel George Morton was flawed. Gould cast Morton as a racist who fudged his data to match his beliefs about white racial superiority because of a supposed larger skull capacity. Instead, the anthropologists argued, it was Gould who manipulated the data to support his biases. This ignited a series of follow-up articles in the scholarly literature by authors taking a variety of positions regarding Morton’s data and Gould’s interpretations. Weisberg believed that the re-analysis was flawed and Gould was mostly correct. Kaplan and his colleagues claimed that Morton’s interpretations were flawed, but that Gould was incorrect in believing that he could discern Morton’s actions and motivations. Finally, Mitchell believed that Morton’s data were accurate and that the interpretations were colored by the racism of the era, but the claim that Morton subtly manipulated the data was a fiction created by Gould.