The investigation of intelligence in humans may have taken a step forward, thanks to a study done on chimpanzees.

Human intelligence is difficult to quantify. Much of what is considered intelligent in humans is determined by society. Although genes play a role in the development of intelligence in humans, external forces can also greatly influence mental capacity. Childhood events and upbringing can also become a major factor in determining results on such tests.

Therefore, investigators wishing to examine human intelligence often examine chimpanzees to study our own species. These animals are similar to humans on a genetic level, and are highly-intelligent. Tests of intelligence quotient (IQ) can often be influenced by the social and economic status of human participants, but is eliminated in studies of the primate.

Earlier studies tended to classify all members of a species as having similar levels of intellect. Only in the last few decades have researchers started to seriously investigate differences among the animals, as well as social factors in animal studies. Environmental factors were believed to play a small part in shaping behavior, while genetic influence was maximized. This new study shows genes may play a larger role than once believed in chimpanzee, and perhaps human, behavior.

Georgia State University scientists, along with researchers from the Yerkes National Primate Center, conducted a study of chimpanzees. They studied a group of 99 individuals, ranging in age from 9 to 54, for whom they had family records.

The group administered the Primate Cognition Test Battery to the animals. This set of simple tests measure mathematical reasoning, spatial cognition, social skills and understanding of cause-and-effect.

Results from the tests were then compared to those of relatives. The team found roughly half of chimpanzee intelligence was carried by genes, while the remainder was due to environmental forces. Spatial and social communication skills were shown to be most-influenced by heredity.

Researchers discovered that chimpanzees raised by humans were not any more, or less, intelligent than those brought up in the wild.

"Chimps offer a really simple way of thinking about how genes might influence intelligence without, in essence, the baggage of these other mechanisms that are confounded with genes in research on human intelligence," William Hopkins of Georgia State University, said.

Of the 99 animals studied, 86 were given a second round of tests. The results of this follow-up research confirmed the initial findings. It also revealed that intelligence of chimps, like humans, does not seem to change over time.

Study of chimpanzee intelligence and what it can tell us about the development of our own species is detailed in the journal Current Biology.

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