Human evolution tied to a small fraction of the genome

Only about 7.5 percent of the human genetic instruction book shaped the evolution of human traits, a new study suggests. And it’s often not genes, but the how-to instructions for using those genes that are most important, researchers report January 19 in Nature Genetics.

Those findings emerged from a new method of analyzing how natural selection has tinkered with the genome since humans split from chimpanzees.

“Remarkably we use nearly the same building blocks as chimpanzees, but we end up with very different results,” says Brad Gulko, a computer scientist at Cornell University.

Previously, researchers have mostly looked for evolutionary clues in protein-producing genes because proteins do much of the important work in cells and organisms. Altering a protein may change the way an organism looks or acts. But mutations that alter proteins often are devastating to an organism and therefore aren’t passed on to offspring.

Gulko and colleagues found that only 9 percent of the DNA that got evolution’s attention resides in protein-coding parts of the genome that are shared with other species. About 52 percent of the places showing signs of natural selection were in intergenic regions, the stretches of DNA between genes. Another 35 percent were in introns — spacer DNA found within genes but not involved in encoding proteins. Both intergenic regions and introns often contain DNA responsible for controlling gene activity.

These findings suggest that human evolution works mostly through changes in how genes are used, rather than by altering genes and the proteins they encode.