Only a few wild gorilla groups are habituated to human presence, and those that are tend to linger where their behavior remains out of view, Breuer said. The observation of gorilla tool use came after more than 10 years of continuous monitoring at Mbeli Bai.
Though tool use is likely infrequent among gorillas, the new evidence provides insight to how gorillas see the world and interact with their environment, Breuer said.
"The most fascinating thing about this observation is the similarity [to humans] with which the gorillas solve the problems in this particular habitat," he said. "If you or me want to cross a swamp, we use the same solutions as gorillas."
Like humans, the gorillas in the swampy clearing jump from one dry patch to another, walk over branches, swing from trees, andas the observations and photographs now showuse tools.
Evidence that all great ape species use tools also adds insight to human evolution, Breuer added. It suggests that tool useonce thought a distinguishing characteristic of humansemerged in primates before humans split from the great apes.
Most observed instances of tool use in great apes are directly related to processing food, such as chimpanzees using sticks to fish for termites and rocks to crack nuts.
The use of sticks by gorillas for postural support suggests tool use can be triggered by other environmental factors. It also fits with the argument that tool use reflects ecological needs, Breuer and his colleagues conclude in PLoS: Biology.
Stanford, the University of Southern California anthropologist, said the tool use of gorillas is "lower order," in the sense that their tools are not modified like the sticks chimpanzees use to fish for termites. Nevertheless, he added, the finding is "very cool."
According to de Waal of Emory University, the observation is "a major step in our knowledge of the gorilla, who has now joined the technology crowd among our close relatives."
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