Chimps are about 96 percent genetically identical to humans, and like us they are self-aware enough to recognize themselves in a mirror.
But physically, we show some remarkable differences. They don't get the same kind of heart disease humans get. They develop some of the brain abnormalities associated with Alzheimer's disease, but not others. And despite being more sexually promiscuous than humans, they don't get the same sexually transmitted diseases.
They heal better than we do and don't get sleep apnea, hemorrhoids, varicose veins, or acne. They aren't vulnerable to cancers of the breast, lung, stomach, pancreas, colon, ovaries, or prostate.
Physician-scientist Ajit Varki says these differences can be as informative as the similarities. With new restrictions expected soon on the use of chimpanzees in research, he and other scientists spoke about some types of research not mentioned in a new report, which they hope will continue or even increase.
The changes are expected to follow an Institute of Medicine report, released earlier this month, that stressed that biomedical research should be necessary, behavioral studies should be noninvasive, and animals should be housed and cared for appropriately. It was hailed as a positive step by animal-welfare advocates, such as the American Anti-Vivisection Society in Jenkintown. (According to the society's Sue Leary, there are currently no research chimpanzees in Philadelphia.)
The report said that most current research on chimpanzees is unnecessary. In response, the National Institutes of Health has called for a moratorium on new grants for chimp research until the agency can implement IOM's recommendations. But the new guidelines are not specific enough for scientists to predict which research projects will get the ax.
Some types of research should actually increase, said Varki, including studies that monitor the health of chimpanzees in research centers and sanctuaries. These, he said, can be conducted as part of the chimps' health care and can potentially benefit chimps, since they suffer their own unique set of health problems.
His bottom line is that scientists shouldn't do anything to a chimp they wouldn't be able to do ethically to a human. Researchers, he said, should consider invasiveness as well as any potential benefit to the chimps. Those criteria were not mentioned with regard to biomedical studies.
Varki said there is also a great deal we can learn through autopsy, and yet many sanctuary-housed chimps are incinerated when they die. Sanctuaries are not funded for autopsies or providing samples taken during routine medical care. "It's a lost opportunity to learn about them and us," he said.
Our opportunity to study chimps is also winding down. They are no longer imported for government-funded research. Research chimps are not bred in captivity, and, according to one estimate, will die out by 2037. Chimps in the wild are endangered, and may disappear as well.
Until that time, there is much that can be learned about ourselves from studying chimp behavior, said Emory University psychobiologist William Hopkins. Our evolutionary cousins are helping us understand the nature of our own language, culture, self-awareness, and social relationships. Studying chimps is helping us understand what makes us human.
"They exhibit abilities that other animals don't, so they occupy this unique niche in terms of information about how the brain works and how cognition evolved," Hopkins said.
He also sees no ethical problems with the behavioral work he is involved in at Yerkes National Primate Center, near Atlanta. Some of the studies involve brain scanning, but chimps can't sit still in a scanner without sedation. While darts are sometimes used to anesthetize dangerous animals, Hopkins said workers at Yerkes have trained chimps to accept getting a shot. That limits stress, which improves the accuracy of the scanning.
He is now investigating a form of nonverbal communication called joint attention, which happens when an individual looks at something and others follow his gaze. About 75 percent of chimps do this readily and the remaining 25 percent do not, he said. Genetic studies show those failing to follow another's gaze tend to have an altered form of a gene that codes for a hormone called vasopressin, implicated in bonding and social behaviors.
He also has found that chimps have varied and complex personalities. Some are more extroverted than others, some are more conscientious, and some are more neurotic, said Hopkins. "There are Woody Allens of the chimp world," he said.
He said he believed that the new guidelines might have little effect on behavioral research, and that they were more likely to restrict invasive biomedical studies.
Whether such studies will continue may hinge more on the potential benefit to human health. The IOM panelists were divided over the use of chimps to study Hepatitis C vaccines. The disease kills people, and chimp research may advance the search for a vaccine. But the process - infecting healthy chimps and subjecting them to liver biopsies - is not something any scientist would do to humans.
Regardless of how NIH decides to go on this, there's an unmistakable trend away from invasive research. "Seventy years ago chimps were sent off into space, given lethal doses of radiation, or infected with leprosy or TB," Varki said. "That kind of thing is fading away."
Some of this change comes from our understanding of evolution. "Chimpanzees are our closest relatives in the animal kingdom," said NIH Director Francis Collins. The connection between evolution and animal rights was an underlying theme in the film Planet of the Apes, in which two chimp scientists became enlightened about human rights as they recognized an evolutionary relationship between themselves and human beings. Now we seem to be moving in the same direction.