What If (Almost) Every Gene Affects (Almost) Everything?

Three Stanford scientists have proposed a provocative new way of thinking about genetic variants, and how they affect people’s bodies and health.

In 1999, a group of scientists scoured the genomes of around 150 pairs of siblings in an attempt to find genes that are involved in autism. They came up empty. They reasoned that this was because the risk of autism is not governed by a small number of powerful genes, which their study would have uncovered. Instead, it’s likely affected by a large number of genes that each have a small effect. Perhaps, they wrote, there might be 15 such genes or more.

Two decades later, that figure seems absurdly and naively low. If you told a modern geneticist that a complex trait—whether a physical characteristic like height or weight, or the risk of a disease like cancer or schizophrenia—was the work of just 15 genes, they’d probably laugh. It’s now thought that such traits are the work of thousands of genetic variants, working in concert. The vast majority of them have only tiny effects, but together...