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Jonathan Pritchard, fascinated by evolution since childhood and gifted in math, combines computation and population genetics
to learn how natural selection has influenced our genomes.
This “struggle for life” tends to perpetuate favorable traits, enabling populations of organisms to adapt to their environments. Yet the struggle reveals an amoral ruthlessness at the heart of nature. When Darwin reflected, late in life, on his loss of faith, one consideration he cited was “the sufferings of the millions of lower animals throughout almost endless time.”
Humans are not exempt from this competition for reproductive success. The miscarriage of a fetus, the death of a child from disease, a young couple's inability to have children—all are more than human tragedies; they also prevent particular versions of genes from passing into future generations. As Darwin said of his theory, “the vigorous, the healthy, and the happy survive and multiply.”
Jonathan Pritchard, an HHMI investigator at the University of Chicago, has been fascinated by evolution and natural selection ever since he began collecting insects and watching birds near his childhood home outside London. “Understanding the role of selection in any species is one of the fundamental questions in biology,” he says.
It's also a problem with many practical applications. Selection modifies genes that influence our phenotypes—our biological forms and functions—including susceptibility to disease and responses to environmental toxins. If geneticists like Pritchard can identify places in our genomes shaped by selection, they might shine a spotlight on genetic regions implicated in some of the major scourges of humanity. “Selection could influence common diseases—like diabetes, hypertension, and stroke—that fill up hospital beds,” says his University of Chicago colleague Anna Di Rienzo.
More controversial issues are at stake. Some biologists claim that the biological differences between human populations are largely the product of selection. They say that skin color, body shape, and even certain dispositions such as aggressiveness and intelligence are the product of people with particular heritable traits having more successful offspring.
Other biologists scoff at these claims. They insist that complex characteristics like intelligence depend much more on a person's experiences than on the genetic differences between individuals or groups of people. And they claim that, for most traits, factors like the movement and growth of human populations are more likely than selection to determine genetic inheritance.
Pritchard, a lanky ex-athlete who exudes the calm of a serious runner, has been at the forefront of these controversies throughout his research career. But he has served more in the role of mediator than combatant. Pritchard is an expert at the mathematical techniques needed to determine how natural selection has influenced our genomes. While others argue in the abstract about how genes might affect human traits, Pritchard focuses on facts: what historical processes could have produced the sequences of genetic letters in our DNA?
Photo: Kevin J. Miyazaki