Eli5: why do the vast majority of mammals walk on 4 legs, while humans only walk on 2?
In: 2
Because 4 legged locomotion is just plain easier and more efficient. Pretty much any 4 legged animal can outrun a human, and standing upright doesn’t require as much active effort. The amount of adaptation to our spine and pelvis to allow 2 leggedness is just silly, and it’s causing us back issues and difficulties with birth, compared to other mammals. Notice how other two-legged creatures, like birds, aren’t actually upright. The spine and pelvis just are not meant to do that, ours are a barely-functional evolutionary hack.
But it seems that our ancestors benefited from 2 leggedness in the form of improved tool usage. As in, if you’re already carrying something you’re gimping your four legged locomotion anyway (like a chimp or gorilla), so you might as well get good at the whole bipedal thing instead. At least that’s the most convincing hypothesis for our evolution that I’ve come across. That, or when transitioning from trees to the ground, it was easier to move from knuckle walking to upright walking (and get that sweet free-hands bonus), than it would have been to go full efficient quadrupedal.
Latest Answers