“When we discuss life history of animals, we discuss them as altricial or precocial. Altricial animals produce large number of offspring with a relatively small energetic investment in each one; therefore, the offspring are born pretty weak and many will probably die. Cats, mice, dogs – any animal that produces a litter is probably altricial. Other animals are precocial. That means a large energetic investment goes into each offspring; they usually reproduce one at a time and their offspring are born pretty ready to handle a lot on their own. Think of elephants, horses, whales, and so forth: long gestation periods, and offspring born capable of pretty full locomotion. Humans are the odd case. We are secondarily altricial. Our reproductive strategy looks like that of a precocial species – one progeny at a time and a substantial resource investment in each – but our infants resemble altricial infants much more than precocial ones.
Human life history only make sense if you look at human infants as fetuses that are continuing to develop outside the womb, and happen to have been born prematurely. In fact, up until it reaches eight months to a year of age, it is much more consistent with developmental understandings to see any baby as a prematurely born infant. Therefore, most of the development that you see in an infant is that which would “normally” take place in the womb. This is because, quite frankly, our large brain size prohibits birth at full brain weight. Most precocial mammals are born with brains fairly close to adult brain size; we do most brain development outside the womb that other precocial species do inside.”
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