From Science:
Humans and chimpanzees share at least 98% of their DNA, yet chimps are an endangered species while people have used their superior cognition to transform the face of the Earth. What makes the difference? A new study suggests that evolutionary changes in the regulation of a gene implicated in perception, behavior, and memory may be partly responsible.
Thirty years ago, geneticist Mary-Claire King and biochemist Allan Wilson proposed that changes in how genes are regulated, rather than in the proteins they code for, could explain important differences between chimps and humans (Science, 11 April 1975, p. 107). To test this hypothesis, an international team led by evolutionary biologist Gregory Wray of Duke University in Durham, North Carolina, focused on the gene that codes for the protein prodynorphin (PDYN), a precursor to a number of endorphins, opiatelike molecules involved in learning, the experience of pain, and social attachment and bonding. Humans carry one to four copies of a region of DNA that controls the expression of this gene. Human copies had five DNA mutations not seen in the other primates. The team concludes that the pattern is a solid example of natural selection acting on the human lineage after it split from the chimp line from 5 million to 7 million years ago.
More here.