On the ever-shrinking list of behaviors unique to humans, one stands out: selfless altruism.
Or so scientists thought. Even as they dismiss many of the kindnesses we do for others as selfish rather than selfless (that is, we help someone because we expect, even subconsciously, a favor in return one day, or because it makes us feel good), they concede that humans have the capacity to act on behalf of others even when there is no prospect of personal gain and even if it comes at a cost. In that, supposedly, we are unique.
Just as tool use and weaponry and culture and symbolic communication were once thought to be unique to humans but have now been found in chimps and other species, however, so has altruism. In a study in the open-access (that is, free) journal PLoS Biology, biologists led by Felix Warneken of the Max Planck Institute for Evolutionary Anthropology found that chimpanzees act altruistically toward unrelated and unfamiliar chimps, with no expectation of reward and even when some effort is required.
That was supposed to be the sole province of Homo sapiens. Chimps do nice things for each other—they share food, groom their friends, console troop-mates and form alliances against opponents—but in every case the action can be explained by increasing the chance that the do-gooder will either be on the receiving end of such a kindness in the future (you groom me, I’ll groom you) or will increase the chance that his relatives will survive and reproduce.
Still, there had been hints of pure altruism. In a 2006 study, for instance, scientists reported that chimpanzees helped their human caregiver fetch objects she was unable to reach. This was the first experimental evidence that chimps are capable of altruistic helping, but even it came with an asterisk: maybe the chimps hoped to eventually be rewarded for their kindness, which would make it less-than-pure altruism.
To see just how selfless chimps can be, Warneken’s team tested 36 of them, as well as 36 human toddlers (18-month-olds). The basic idea was that a person neither the chimps nor the toddlers had seen before would look at a wooden stick or a pen that had been placed just out of reach. The chimps were able to reach the stick, and the babies the pen. Sometimes the stranger reached for the stick or pen, unsuccessfully, and sometimes they just looked at; sometimes the stranger had a banana (for the chimps) or a little toy (for the toddlers) that he or she would give out as a reward for being helped.
There were several permutations of reaching/not-reaching, reward/no-reward. The rationale was this: if toddlers and chimps “are responsive to the [stranger’s] goal, they should hand the object more often in reaching than in no-reaching conditions. If they are primarily interested in their own immediate benefit, they should help more often in reward than in no-reward conditions.”
When all was said and done the answer was clear. Twelve of 18 chimpanzees and 16 of 18 toddlers helped when the stranger reached for the stick or pen. For both toddlers and chimps, what determined whether or not they helped was whether the stranger tried to retrieve the object, not the prospect of a reward.
“This indicates that subjects were motivated to help the experimenter with his/her unachieved goal . . . but did not aim at retrieving a material reward for themselves,” write the scientists. “Rewarding their helping was unnecessary and did not even raise the rate of helping in either case.” The altruism held up even when it got harder to help—when the scientists placed the stick in such a way that the chimps had to run along an elevated “raceway" to retrieve it, and when they blocked the way to the pen with barriers the kids had to scramble over and around.
But would chimps help other chimps? Earlier research had said no, but in those experiments the animals were preoccupied with getting food for themselves and didn’t stop to offer help to another chimp. So the German scientists set up something simpler. They placed food in a room and chained the door shut. The chimps could see all of this. They could also see a second chimp, a stranger, try to get into the room.
The chimps came through again. When they saw the second chimp needed help to get into the dining room, they helped up to 89 percent of the time—even though there was nothing obviously in it for them.
The finding that chimps can act selflessly suggests that the evolutionary roots of human altruism run deep, to at least the last common ancestor of humans and chimps.