“So brain size cannot be the single explanation for what we can do with our neural machinery,” he says. Having a bigger brain doesn’t mean that you’re better at the aspects of cognition that we consider uniquely human, like language and understanding others’ mental states, Sherwood says. “There must have been some adaptive value to brain size increase.” Evolution is frugal and cost-effective, and brain tissue has extraordinary metabolic expense,” he says. “Brains don’t just do that for no reason in evolution. This work has revealed that, over the last three million years, brain size roughly tripled in the human lineage, from about 450 grams (or about the size of a large orange) in our ancestor Australopithecus afarensis (the same species as the famous Lucy fossil) to between 1,300 and 1,400 grams in modern humans.Īll of this happened, Sherwood says, without much of a change in body size. The skulls can be filled with a casting material like latex to create a rough model of the brain called an endocast, or, more commonly, scientists use computerized tomography (CT) to scan the skull and create a digital representation of the brain. By studying the fossilized skulls of human ancestors, scientists have been able to estimate the size of the brains the skulls once housed. Scientists have learned that a tremendous amount of brain growth took place in the human lineage. Modern humans have brains that are three times bigger than those of our closest living relatives, chimpanzees, suggesting that something special occurred in our evolution. “Brain size expansion is one of the most extraordinary features of human brain evolution,” says Chet Sherwood, an anthropologist at George Washington University who studies primate brain evolution. What is it about the human brain that enables us to do these things? What unique features can account for our cognitive abilities? In many ways, the study of human brain evolution is the search for these features and how they came about. These baby steps would have been critical for the long childhood that is now often regarded as a keystone of human uniqueness.Courtesy, with permission: Aida Gómez-Robles and José Manuel De La Cuétara.Īs humans, we do things that no other animal does. Extended brain growth in Lucy’s species may have provided a basis for the subsequent evolution of the brain and social behaviour in our ancestors. Lengthening the period of brain growth also stretches out a species’ highly impressionable learning period. And this can be linked to a long reliance on caregivers. Slowing brain development is a way to spread the energetic needs of highly dependent offspring over many years. Thus, this species may bridge the gap between the long childhoods humans enjoy today, and the shorter ones of our ape-like ancestors.Īmong primates in general, different rates of growth and maturation are associated with varied strategies of caring for infants. Our estimates suggest that by 2.4 years old, australopithecine children had brains that were only about 70% as big as adults, while average chimpanzees of the same age would have completed more than 85% of their brain growth. Virtual models of australopithecine brain cases reveal members of Lucy’s species had a chimpanzee-like brain organisation, but grew for a longer period of time. Surprisingly, however, its rate of brain development seemed to have shifted from the fast lane to the slow lane. This means the infant grew its molar teeth rapidly – similar to chimpanzees, and faster than humans. Our team’s dental experts calculated an age of 861 days, about 2.4 years. Having access to precise records of the Dikika child’s teeth, we were able to determine how old the child was when it died. The lengthy childhood of endangered orangutans is written in their teeth Similar to the growth rings of a tree, cross sections of teeth also reveal daily growth lines reflecting the body’s internal rhythms during childhood. The truth is in the toothĪ seldom recognised fact about humans and other primates is that our milk (baby) teeth and first molars are marked with a line formed at birth. Synchrotron imaging can also provide powerful insights into dental development. By forcing electrons to travel in a circular direction with magnetic fields, extremely bright light is produced that can be filtered and adjusted for research purposes.Ī benefit of this approach is that permanent impressions of brain folds on the bone can provide clues about key aspects of the brain’s organisation. This 3D animation shows the skull of the Dikika child.Ī synchrotron is a machine that accelerates electrons close to the speed of light and directs them around a large ring.
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