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Interesting how much a child’s growth slows before puberty. 90% of brain volume is present at age 5. So there's a long period in which the brain is mostly developed, where the child doesn’t physically grow that much.
Is there a known explanation of this?
My first thought is that most learning benefits from a big brain but not from a bigger body. E.g. A bigger body is irrelevant for learning language, socialization, and general knowledge. Moreover, it’s probably easier to learn motor skills with a smaller body because you can fall over more times (mass scales cubically) and it’s easier for parents to control kids with smaller bodies while they are still learning impulse control. Brains and bodies both have substantial metabolic costs but the costs of the post-puberty body are not worth it during this period.
Some recent papers claim that adolescent growth spurts are also found in bonobos and other primates. So this growth pattern is not unique to humans — though I assume humans have the longest period in the slow-growth mode.
