Chimp brains don’t shrink

Unlike humans, chimpanzees’ brains don’t shrink as they get older. That means that, so far, people seem to be the only lucky species whose brains wither with age, researchers report online July 25 in the Proceedings of the National Academy of Sciences.

“Chimp aging seems to be on a different trajectory than humans’,” says aging and Alzheimer’s expert Caleb Finch of the University of Southern California in Los Angeles, who was not involved in the study.

So far, the small number of great ape brains that have been studied show mild changes with age, Finch says, but nothing that approaches the damage seen in the brains of people with Alzheimer’s disease. Understanding differences in aging between humans and other primates may help scientists figure out why human brains are susceptible to age-related dementias.

In the new study, anthropologist Chet Sherwood of George Washington University in Washington, D.C., and colleagues focused on chimpanzees, which have some of the most developed brains and longest life spans among primates. The researchers wondered if chimps experience brain decline in old age similar to that seen in humans.

The researchers scanned the brains of 99 chimpanzees with ages representing the entire adult life span, from 10 to 51 years. For comparison, the team imaged the brains of 87 humans from 22 to 88 years old. 

The human scans confirmed what other studies had found: All brain regions measured showed shrinkage with age. But chimp brains didn’t get smaller with age.

Sherwood points out that the results don’t answer a fundamental question for human evolution: “Why would we be built in such a faulty way that leads to this degeneration in our brains?” he asks. Perhaps a long life span is worth the drawback. Big brains and long life spans may free up older members of the population to look after the youngsters, he speculates.