It's another one of those questions that pops up, unbidden, just before sleep or while free-associating during interminable election seasons: Why do human babies take so long to learn to walk? Baby giraffes are up and walking within an hour of birth -- and that's after absorbing a six-foot drop.
As Julian Huguet explains in today's DNews dispatch, it's all about brain development.
The human brain, it turns out, is nowhere near fully formed at birth, which goes a long way toward explaining why babies suck at chess. Human babies have underdeveloped brains for a reason, however: We need big skulls to house our oversized brains, and those skulls -- if fully formed -- could not squeeze out of the birth canal.
Our very predilection for walking upright also comes into play here. When human first came down from the trees and getting off all fours, our upright stance caused our hips to change. Our new evolved hips caused a narrowing of the birth canal.
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Thus we have the evolutionary catch-22: Walking upright requires a big brain, but we can't get those big brains out of the birth canal to walk upright in the first place. To get around this dilemma, nature has arranged things so that we're born with underdeveloped brains. The bones in our skull have not yet fused at birth, and in fact the brain nearly doubles in size in our first few years out of the womb.
This necessarily delays our ambulatory development -- we get nine months of brain growth in the womb, but the real heavy lifting starts after we're swaddled up and staring up at that mobile Aunt Carol bought for the crib. Giraffes, by comparison, have a 13-15 gestation period. By the time a baby giraffe drops into the world, all the walking-around components of the brain are ready for action.
In fact, an interesting study out of the University of Sweden in 2009 shed some light on all this. The researchers tracked the brain size of 24 different species of mammal when they first start walking, then compared those dimensions to the species final adult brain size. Taking conception itself as the starting line, humans actually begin walking at the same developmental milestone as other animals.
It's just that animals do their brain development in the womb. We like to work things out on the living room carpet, scaring the cat.
-- Glenn McDonald
National Library Of Medicine: A Unifying Model For Timing Of Walking Onset In Humans And Other Mammals
Scientific American: Are Our Big Brains The Reason Newborns Can't Walk?
Smithsonian Magazine: Becoming Human: The Evolution Of Walking Upright