Human Evolution Caused by Genetic 'Switches': How Our DNA Diverged from Chimpanzees

Chimpanzees are the closest living relatives to humans, and researchers continue to hunt for clues when it comes to understanding how our evolutionary paths diverged. Now, scientists may have the answer. They've found further proof that the divergence of humans and chimps that occurred between four to six million years ago was profoundly influenced by mutations to DNA sequences that play roles in turning genes on and off.

There is actually little difference between humans and chimps when it comes to the proteins produced by genes. In fact, the proteins in the two species are more than 99 percent identical. Despite these similarities, though, humans are obviously vastly different from chimps. This, in particular, is what sparked scientists' interest in the current study.

The researchers combined recent data that identified transcription factor binding sites, data on human genetic variation and genome comparisons between humans and apes. By using a new computational method called INSIGHT (Inference of Natural Selection from Interspersed Genomically CoHerent elemenTs), the scientists were able to integrate these diverse data types and find evidence of natural selection in the regulatory DNA.

Less than two percent of the human genome contains genes that code for proteins. In cells, these proteins are crucial to biological pathways that affect an organism's health, appearance and behavior. Much less is known about the remaining 98 percent, but scientists have recognized that some of the non-protein coding DNA regulates when and where genes are turned on and off, and how much protein they produce.

With that in mind, the scientists found that when compared with protein coding genes, binding site DNA shows close to three times as many "weakly deleterious mutations." These mutations are ones that may weaken or make an individual susceptible to disease, but are not generally severe.

Yet the scientists also found that transcription factor binding sites seemed to show positive selection. This means that they seemed to be responsible for mutations that led to favorable traits and which could eventually increase across a population.

"The overall picture shows more evolutionary flexibility in the binding sites than in protein coding genes," said Adam Siepel, Cornell associate professor of biological statistics and computational biology, in a news release. "This has important implications for how we think about human evolution, and disease."

The findings reveal that these "switches" were probably what helped trigger human evolution all those years ago. In addition, they reveal a little bit more about the state of humans today.

The findings are published in the journal Nature Genetics.