A short paper in PLoS Biology by Thomas Breuer and colleagues describes the first two observed instances of tool use in wild gorillas. Reuters has reported on the research as well.
From the Reuters report:
They describe the two instances in the northern rain forests of the Republic of Congo.
"We first observed an adult female gorilla using a branch as a walking stick to test water deepness and to aid in her attempt to cross a pool of water at Mbeli Bai, a swampy forest clearing in northern Congo," Breuer and his international colleagues wrote.
In the second case, they saw another pull up a dead shrub.
"She forcefully pushed it into the ground with both hands and held the tool for support with her left hand over her head for two minutes while dredging food with the other hand," they wrote. "Efi then took the trunk with both hands and placed it on the swampy ground in front of her, crossed bipedally on this self-made bridge, and walked quadrupedally towards the middle of the clearing."
Since gorillas use tools in captivity, they have long been known to have the cognitive capacity to do so; not unexpected since chimpanzees and orangutans both use tools in the wild and captivity. It seems clear that at least the basic cognitive potential for tool use is very ancient in hominoids, dating at least to the last common great ape ancestor, and quite possibly much earlier.
So the evolutionary question is what causes some lineages to develop this potential in practice, and what causes other lineages to retain more latent abilities. How active a role does ecology have, versus social dynamics? And how much tool use is facilitated by dedicated brain circuitry, versus more generalized cognitive processes that may be adapted to other behaviors?
Observing anything in wild gorillas helps to answer these questions. If gorillas use tools with good facility in captivity, but never, ever, used them in the wild, then it would be a good reason to think that their "cognitive adaptations" for tool use were not particularly adaptations to tool use at all. In this case, the cognitive underpinnings of tool use in great apes would likely reflect adaptations involving other behaviors.
More observations of tool use in wild gorillas reopens the question. Perhaps hominoid brains do have adaptations specific to tool use (or seeing external objects as possible tools), and those come into adaptive importance from time to time.
