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.

Comments

not so fast

[arth1]

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.

Re:not so fast

[Dahamma]

The evolutionary reality is even simpler that that (though the achievement of those is clearly not). The three main factors are:

1. be able to reproduce
2. be able to attract/acquire a mate
3. be able to care for/protect offspring long enough for them to reach #1

Clearly if it was just up #1 we would still be living alongside the rest of the primates. #2 can be a fairly complex social interaction - but insects are just as capable of it as humans. #3 is where the whole thing explodes, and is the key to investing all of those resources into the brain (and is what made it more evolutionarily advantageous to extend the time to #1 and #2).

Though of course in modern human society, social and technological advancement in #3 has so outpaced the first two that they barely seem to matter, and is why we are basically blowing past any "natural" population control. Our brains are letting us find clever ways of surviving and stripping the planet of resources, but unless we figure out a way to expand beyond the planet or stop using its finite resources we'll go through the same collapse seen in any other species going through a population explosion...

Re:not so fast

[ShanghaiBill]

growing up fast is what should have been selected.

Not necessarily. The major threat to children in primitive hunter gatherer societies is not predators but hunger. By staying smaller during their formative years, they reduce the amount of calories need to survive. But the selection pressures are different on boys and girls. Girls are generally able to procreate as soon as they reach puberty. But boys need to wait till they are older, and have built up social status. So it makes sense for girls to mature faster, and that is what happens. Look at a group of kids in 4th or 5th grade, and the girls are several inches taller than the boys.

Re:not so fast

[Zuriel]

'Imply' means something different in formal logic. You can use this line instead: "Just because two things happen at almost the same time doesn't prove that the first one caused the second."

The guy who got shot in the brain could have had a heart attack seconds earlier. You still need to do the autopsy to prove that the shot was the cause of death. Yeah, it probably was, but 'probably' isn't proof.

Critical Path

[Livius]

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.

Re:Wrong (but still the brain's fault)

[wonkey_monkey]

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?

Probably because "stealing calories" is just an over-simplified journalistic bit of fluff.

Re:Sperm to frogs

[Anonymous Coward]

I bet diapers are standard gear in space. You cannot shit properly without gravity.

Thank God you both have imagination and speculation to help fill in your gaps in knowledge.

If only someone could invent a vast, searchable information databank that was computer accessible via network where you could answer these inquiries then perhaps you might not be forced to speculate as much. I would call such a thing a CompuNet.

Oh well, we can dream can't we?