From the Niger river to Congo, in the central portion of the range, P. Pan troglodytes verus occurs in the western portions of the range, from Gambia to the Niger river. There are three recognized subspecies of common chimpanzee. They are found from Gambia in the west to Uganda in the east, excluding the region bordered by the Congo and Lualaba rivers in central Zaire (Congo) where their sister species, bonobos ( Pan paniscus), are found. They are distributed from about 10 degrees N to 8 degrees S, and from 15 degrees W to 32 degrees E. "The particular vulnerability of the human brain to Alzheimer's disease suggests that there's something unusual about our brain chemistry.Chimpanzees ( Pan troglodytes) inhabit the tropical forests of central Africa.
"There is the opportunity here for much more microscopic and biochemical work," Preuss told LiveScience. Preuss and his colleagues are studying the subtler differences between human and chimp brains, trying to understand how molecular and cellular variations separate us from our nearest living relatives. In fact, humans outlive their reproductive usefulness for so long that it's amazing their brains don't degrade faster, said Todd Preuss, a neuroscientist at Yerkes National Primate Research Center who was not involved in the current study. "If you're going to take on another 40 years of life span and these neurons have to function, that ultimately seems like it's going to be hard to keep up with," Sherwood said. The cost of having grandma and grandpa around as nannies is that the brain's repair mechanisms may not have evolved to pick up the slack. This longevity may have evolved so that grandparents could help their own children with childrearing, thus ensuring that their offspring's offspring would survive to spread their genes. But human women can expect to live 40 years past menopause. In most mammals, females die once they can't reproduce anymore. Sherwood suspects that as natural selection began to favor the large human brain, humans had to deal with the associated costs, including relatively helpless infants and an extended childhood as that brain develops. That's not to say that chimps' brains don't change with age - other studies show cellular changes and subtle structural changes in animals as they get older - but the direct comparison makes it clear that "whatever is going on is certainly more extreme in humans," Sherwood said. But the chimps' brains showed no size change at all.
CHIMPANZEE AGE SPAN FULL
Thus, the study captured more than the full range of life spans and brain aging that you would expect to see in the evolutionary past of chimps and humans.įocusing on the frontal lobe and hippocampus, the most shrink-prone regions of the human brain, the researchers found the expected loss of brain size with age in the human volunteers. Likewise, studies of foraging communities suggest that the mid-80s is the typical life span for pre-industrial humans. In the wild, Sherwood said, chimps are usually dead by 45. The researchers also examined the brains of deceased chimps as old as 51. The chimps ranged from 10 to 45 years old. Sherwood and his colleagues compared magnetic resonance imaging (MRI) scans of the brains of 87 humans ages 22 to 88 with MRI scans of 69 chimpanzees from the Yerkes National Primate Research Center in Atlanta. In chimps of equivalently old age, the new study finds, there is no shrinkage at all.
In old age, the human brain shrinks in overall size by 10 to 15 percent. The two species have clearly diverged quite a bit during that time period, with one of the less-visible differences occurring in the brain. Chimps and humans are separated by between 6 million and 8 million years of evolution, dating back to the last common ancestor we shared with our ape cousins.
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