Happiness in chimps, as in humans, is strongly influenced by their genetic makeup, according to researchers at the University of Arizona, Tucson. Scientists say such findings demonstrate the usefulness of nonhuman primates as models for human behavior.
To probe chimp contentment, psychologist James King asked volunteers at 13 zoos in the United States and Australia to fill out a questionnaire measuring the "subjective well-being" of 135 chimps. They assessed four factors: the amount of time a chimp was in a "positive" mood; whether the chimp found social encounters "enjoyable" or distressing; how well the chimp met its goals (such as social interactions or obtaining food); and finally, how happy the rater would be to actually be the chimp in question. Happy chimps, says King, are "more self-confident, dominant, protective, and inquisitive," while unhappy ones are "more emotional, timid, and depressed."
Researchers computed the genetic contribution to well-being based on every chimp's relatedness to every other chimp--a total of 9045 pairs in which relatedness ranged from 0 to 75% (for siblings whose parents were also related). They found that genes contributed about 40% to chimp happiness, putting them in the same ballpark as humans, reported grad student Alexander Weiss earlier this month at the meeting of the Behavior Genetics Association in Vancouver. "Most physical effects that cattle breeders breed for tend to be heritable at lower levels than that," says Weiss.
The researchers were able to establish that--as with humans--differences in shared environments (in this case, different zoos) did not influence the happiness differences. Rather, the operative environmental influences are those, such as diet and relationships, that are unique to each chimp.
Psychologist David Lykken of the University of Minnesota, Twin Cities, says the finding is plausible because "there must certainly be some genetic effect [on well-being] in all of us primates due to heritable differences in neurochemical activity." Such studies, he adds, may also "help advance our understanding of human evolution." Weiss says there's a practical payoff, too: High happiness heritability means "that we can breed a happier ape."