A Missing Genetic Link in Human Evolution

 Humans have multiple copies of a gene known as SRGAP2, which is thought to be involved in brain development. Chimps and orangutans have only one copy. Dennis et al., Cell 2012

 

About 8 million to 12 million years ago, the ancestor of great apes, including humans, underwent a dramatic genetic change. Small pieces of DNA replicated and spread across their resident chromosomes like dandelions across a lawn. But as these “dandelion seeds” dispersed, they carried some grass and daisy seeds — additional segments of DNA — along for the ride. This unusual pattern, repeated in different parts of the genome, is found only in great apes — bonobos, chimpanzees, gorillas and humans.

“I think it’s a missing piece of human evolution,” said Evan Eichler, a geneticist at the University of Washington, in Seattle. “My feeling is that these duplication blocks have been the substrate for the birth of new genes.”

Over the past few years, scientists have begun to uncover the function of a handful of genes that reside in these regions; they seem to play an important role in the brain, linked to the growth of new cells, as well as brain size and development. In September, Eichler’s team published a new technique for analyzing how these genes vary from person to person, which could shed more light on their function. [...] simonsfoundation.org