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Male chimpanzees signal their aggression when they display their big canines, in contrast with humans, who show small canines when they smile.
Humans are the ultimate social animals, with the ability to bond with mates, communicate through language, and make small talk with strangers on a packed bus. (Put chimpanzees in the same situation and most wouldn’t make it off the bus alive.) A new study suggests that the evolution of our unique social intelligence may have initially begun as a simple matter of brain chemistry.
Neuroanatomists - Decades - Differences - Brains - Humans
Neuroanatomists have been trying for decades to find major differences between the brains of humans and other primates, aside from the obvious brain size. The human brain must have reorganized its chemistry and wiring as early human ancestors began to walk upright, use tools, and develop more complex social networks 6 million to 2 million years ago—well before the brain began to enlarge 1.8 million years ago, according to a hypothesis proposed in the 1960s by physical anthropologist Ralph Holloway of Columbia University. But neurotransmitters aren’t preserved in ancient skulls, so how to spot those changes?
One way is to search for key differences in neurochemistry between humans and other primates living today. Mary Ann Raghanti, a biological anthropologist at Kent State University in Ohio, and colleagues got tissue samples from brain banks and zoos of 38 individuals from six species who had died of natural causes: humans, tufted capuchins, pig-tailed macaques, olive baboons, gorillas, and chimpanzees. They sliced sections of basal ganglia—clusters of nerve cells and fibers in a region at the base of the brain known as the striatum, which is a sort of clearinghouse that relays signals from different parts of the brain for movement, learning, and social behavior. They stained these slices with chemicals that react to different types of neurotransmitters, including dopamine,...
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