If a chimpanzee appears unusually intelligent, it probably had bright parents. That’s the message from the first study to check if chimp brain power is heritable.
The discovery could help to tease apart the genes that affect chimp intelligence and to see whether those genes in humans also influence intelligence. It might also help to identify additional genetic factors that give humans the intellectual edge over their non-human-primate cousins.
The researchers estimate that, similar to humans, genetic differences account for about 54 per cent of the range seen in “general intelligence” – dubbed “g” – which is measured via a series of cognitive tests. “Our results in chimps are quite consistent with data from humans, and the human heritability in g,” says William Hopkins of the Yerkes National Primate Research Center in Atlanta, Georgia, who heads the team reporting its findings in Current Biology.
“The historical view is that non-genetic factors dominate animal intelligence, and our findings challenge that view,” says Hopkins.
Run the gamut
To assess heritability, Hopkins and his colleagues studied 99 captive chimpanzees – 29 males and 70 females – aged from 9 to 54. The team had the chimps do 13 standard tasks to measure their cognitive abilities.
Hopkins teased out ability in four broad categories: spatial memory and ability; tool use; communication skills; and establishing causality. Tests to remember which of three beakers hid food, for example, helped measure spatial memory, while challenging chimps to obtain visible but otherwise inaccessible food by attracting attention from humans helped measure communication skills. By combining results from all the categories, the researchers calculated values for g.
By taking into account the sex of each animal, its family relationships, and what sort of environment and chimp culture it grew up in, the researchers claim they could isolate the impact of heritability on how well the animals scored. They found that genetic background accounted for 52.5 per cent of the variance in overall g scores. Within the tasks, heritability had the strongest impact on spatial memory and ability, and communication skills.
Hopkins speculates that these skills may be more heritable because they are important in foraging and group problem-solving, which strongly affect survival and mating chances. “Smarter chimps might gain access to more food resources and mates,” he says.
Other intelligence researchers said the results seemed broadly sound. “The discovery that spatial skills have a strong genetic component is unsurprising, but the link with communication needs further investigation,” says Josep Call of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. He led a study in 2012 which found that some chimps were unusually intelligent. Call was also surprised that tool use only showed a weak heritability.
The results were consistent with those in people. “They are bang on with human results in showing substantial g and in showing that results in nearly all of the tests are significantly heritable,” says Robert Plomin of King’s College London, who is a veteran researcher on genetic elements of human intelligence. He also says the study suggests the range of cognitive abilities tested in the chimps are influenced by the same suites of genes.
However, Plomin challenges Hopkins’s suggestion that research in chimps will hasten the identification of genes in humans that influence intelligence. “I think the flow will go the other way, and we’ll find genes associated with intelligence in humans, then ask if the same genes impact intelligence in chimps,” he says.
Journal reference: Current Biology (DOI: 10.1016/j.cub.2014.05.076)