Justin’s Notes

The Same Caveat That Loads the Gun Also Jams It

2026-07-20 · AI-generated insight

Filed together under "Forbidden Inquiry," these three read as a bold heresy against a timid orthodoxy. But read for their actual claims rather than their framing, something odd emerges: the science is far more modest than the transgressive packaging implies, and its modesty comes from a single shared crux.

The ancient DNA paper is the natural engine for everything Reich and Warne want to argue. If "many hundreds of alleles" underwent strong directional selection in just the past ten millennia—including alleles that today predict cognitive performance—then population differences in trait-linked genetics are not only conceivable but expected. This is the mechanism that would make Reich's "we can no longer ignore average genetic differences" bite, and it supplies the deep-time backdrop for Warne's converging lines.

Yet the same paper disarms the inference in its own sentence: those cognitive effects "were measured in industrialized societies, and it remains unclear how these relate to phenotypes that were adaptive in the past." The polygenic scores that detect the selection are validated only where they were built. That is precisely the fault line Warne is forced to honor when he quarantines his entire argument to "native English speakers born in the United States and not necessarily to any other human populations," and reduces the conclusion to a bare ">0%" with the true magnitude "not known."

So the portability of polygenic scores across populations is simultaneously what makes the group-difference hypothesis biologically plausible and what prevents it from being cashed out. The provocative "forbidden" framing obscures how radically the researchers hedge. The interesting question these notes jointly raise is not whether inquiry is suppressed, but whether the honest version of the claim is exciting enough to be forbidden.

Woven from these notes

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.”
— David Reich How Genetics Is Changing Our Understanding of 'Race'
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.
Ancient DNA reveals pervasive directional selection across West Eurasia
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.
— Russell Warne Between-Group Mean Differences in Intelligence in the United States Are >0% Genetically Caused: Five Converging Lines of Evidence