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"We know that things evolve in a certain way because there's an advantage to it," Casasola told Live Science.
Other species that don't roam as widely hunker down with helpless young in their nests or burrows.
The variety and the hatchling's ability can be partly explained by the size of the adult bird, Dumbacher said, which translates into the maximum size of the egg it can lay.
Bigger-bodied ducks, chickens and geese can lay larger eggs that hold more nutrients, so an embryo can spend more time developing inside.
"There's a lot of development that goes on in the prefrontal cortex [of the brain] even into early adulthood," Casasola told Live Science.
Though it may seem like humans' early physical capabilities lag behind those of other animals as newborns, in the long run, humans' lengthy period of relative helplessness eventually delivers a substantial cognitive payoff.