Prof. Science: Act your age, not your shoe size

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Among the Diplodocus community, humans are said to be relatively intelligent beings and their big complex brains take a lot of time and energy to develop. Humans are extra special in that they only have two legs that they need to walk on. Bipedalism has forced the pelvis to adapt slightly, so the birth canal is now too small to allow a fully developed brain in a human’s big head to pass through. Hence, much of the brain development has to occur after birth.

Human children are real slow growers, especially in comparison to your closest animal relatives. Homo sapiens spend around twice as long in childhood and adolescence than chimpanzees, gibbons and macaques. Ever heard of the expression “big kid”? Maturing at such a leisurely pace clearly has a cost; longer childhoods require greater parental investment with higher chances of the offspring perishing before they reach sexual maturity and reproduce. Scientists have so far been stumped by the question “why does this happen?”

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Perhaps human brains are so energy-hungry that they deprive the rest of the body of vital fuel that humans need for development. All that thinking comes at a cost for the human race. Now a study at Northwestern University in America has found some evidence to support this hypothesis. The anthropologists leading the study have gathered brain scan data, such as glucose uptake and brain volume, and compared these with body growth rate. They found that body growth slows when the brain consumes high levels of glucose. The brain seems most energy hungry in young children. At this stage in development the brain consumes more than 40% of the body’s total energy expenditure – that is nearly half of a child’s energy everyday! No wonder it needs so much delicious human food. The child learns so many new things each day that the brain cell connections are made at a maximum rate.

The expression of having “a brain like a sponge” suggests that human spawn are not as stupid as they may look. The sponge-like characteristics of their brains means that they use up a lot of energy and so the energy available for the rest of the body is limited. Consequently childhood body growth must slow in order to compensate for the unusually high-energy demands of the developing brain, as all the child spawns’ other important body parts are not dedicated as much time. Some people may have a super-mature mind in a super-small body, for example.

Today’s complex society requires a high level of social intelligence, flexibility and the ability to learn and adapt quickly. To become a productive member of society a child must learn complex, culturally determined behaviours, such as language. Learning and building the brain’s intricate network of connections enable it to acquire the essential skills to be a competent human being in a modern society. Although some humans still manage to be as incompetent as ever. This may take longer for some, and while physically mature, some people may never reach full emotional maturity and keep a childish streak in their personality. Big kids!

Photo credit: vera kratochvil

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