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Why Do Humans Grow Up So Slowly? Blame the Brain
sciencehabit (1205606) writes Humans are late bloomers when compared with other primates — they spend almost twice as long in childhood and adolescence as chimps, gibbons, or macaques do. But why? One widely accepted but hard-to-test theory is that children's brains consume so much energy that they divert glucose from the rest of the body, slowing growth. Now, a clever study of glucose uptake and body growth in children confirms this 'expensive tissue' hypothesis.
That there is an inverse correlation between brain glucose use and body growth does not imply that the brain's use of glucose stymies the growth until later.
If that were the case, kids who are overfed carbohydrates would be smarter and taller, not fatter and dumber.
My guess is that slow growth is selected for because children who look like children enjoy special care and protection by adults. Growing to adult size by age 7 might be detrimental to survival.
I would speculate that it's simply that, for humans in their eusocial foraging societies, brain development was the priority and there was no point in reaching sexual maturity and adulthood before the brain had developed and the individual had learned enough to be a full member of the community. The brain and the rest of the body are not competing for glucose, the brain is simply the critical path and the rest of the body has no need to develop faster.
You have to clean out the pipes every once in a while before the sperm, well, mature.
For most species, childhood is all risk, no benefit (where benefit = breeding), and so it is to be got through as fast as possible (or at least in time for next breeding season). If glucose shortage was the only reason for doubling the length of our childhood, there would be a huge evolutionary pressure towards kids who could metabolize much more food and reach adulthood in half the time.
There is an obvious reason why humans have such a long childhood - it is because we have so very much to learn. Little bodies can learn as well as big bodies, and cost less to maintain.
Quattuor res in hoc mundo sanctae sunt: libri, liberi, libertas et liberalitas.
If it is the brain stealing calories that slows development, how come when you feed a child a high-calorie diet he becomes a fat child rather than a young adult?
How about this: if we took only three years (or less!) to reach adulthood like some animals, you'd have toddler with an adult body. I'm pretty sure it's actually an advantage that our young are easily restrained. It's actually rather common for more intelligent creatures to take longer to mature. Taking longer to prune the excess synaptic connections seems to allow for greater learning at the cost of slower development. In the case of humans, we're also born with an especially undeveloped brain and a squishy skull, for which your mother is probably grateful.
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humans are not an eusocial species.
I decided to fact check this claim. Eusociality, according to Wikipedia and the references it cites, is defined as three aspects of the behavior of a species:
I agree that humans are not as close to the eusocial ideal as bees and mole rats, but we're closer than a lot of other species.
WE have some wierd fetish with letting kids be kids for as long as possible. Sorry but at 13 you are biologically an adult so you need to have adult responsibilities and adult expectations. these teenagers need to get off their asses and work, build, etc.. Instead we extend this out to age 20 before we expect them to get a job and start being responsible.
Less than 100 years ago it was not uncommon for marriage at age 16 and that young couple working hard to build their family Average age of a woman getting married was around 21 years of age. Today it is far higher at 26 years of age and insanely uncommon for a 16 year old marriage, Although outside the USA it is far lower. Mexico has a median for women at around 18 years old. Many states in the USA still have the age of consent at age 16. This means that 16 year olds can make decisions as an adult, yet for some reason we think they cant today and are still children.
Note on marriage ages, some of this is economics, back 100 years ago it was a lot easier to make a living as you made about $35.00 a month working at a foundry or smelter and typically renting a house is $5.00 a month less that 20% of your income was your rent. today most of the young pay 60% of their income as rent and have to split that rent with room mates because they can not even hope to even meet rent with their meager income. So 100 years ago it was easier for young and uneducated to make it in the world with the sweat of their brow.
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