In February 2011, a team of scientists led by Peter Walsh at the University of Cambridge injected six captive chimpanzees with an experimental vaccine against the deadly Ebola virus. At first glance, the study looked like a lot of other medical research, in which drugs that are meant for humans are first tested on other animals. But this was different. These scientists were working with chimps to help chimps.

The twin threats of poaching and habitat loss are driving the African apes—chimps, bonobos, and gorillas—towards extinction. Diseases are also a problem. Our ape relatives are vulnerable to infections like anthrax, malaria, and respiratory viruses that spill over from human tourists and researchers.

They can also get Ebola. Under a microscope,