Ninety-six percent of a chimpanzee's genome is the same as a human's. It's the other 4 percent, and the vast differences, that pique the interest of Georgia Tech's Soojin Yi. For instance, why do humans have a high risk of cancer, even though chimps rarely develop the disease? In research published in September's American Journal of Human Genetics, Yi looked at brain samples of each species. She found that differences in certain DNA modifications, called methylation, may contribute to phenotypic changes.