You remember what neoteny is—I talked about here: the retention, by adults in a species, of traits normally seen only in juveniles, though a slowing of somatic development.
Obviously, the only way to study this is by comparing it to other individuals, either earlier in the evolution of the species, or in closely related species.
The idea that humans are a neotenous species is somewhat controversial, but there are good arguments in favor of it. A famous proponent of the idea was Stephen Jay Gould, to whom I haven’t been particularly kind.
Comparison to other primates especially seems to support the hypothesis. The picture to the right is a juvenile chimpanzee, probably our closest relative. The similarities in bone structure are uncanny. Another thing we seem to have in common with young chimps is our ability to learn. This is something older chimpanzees mostly lose, but humans retain it throughout their life. I’ve heard that until they’re about two years old, mental development of humans and chimpanzees is about equal. I can’t seem to find a source for this now, though.
Other physical features that speak for our neoteny: our flat-faced orthognathy, reduction of lack of body hair, the form of the external ear, the epicanthic (or Mongolian) eyefold, the central position of the foramen magnum (they hole at the base of the skull; it migrates backward during the ontogeny of primates), high relative brain weight, persistence of the cranial sutures to an advanced age (joints between bones of the skull), the labia majora of women, the structure of the hand and foot, the form of the pelvis, the ventrally directed position of the sexual canal in women, certain variations of the tooth row and cranial sutures, absence of brow ridges and cranial crests (the picture to the left compares adult and juvenile human skulls to capuchin monkey skulls; I couldn’t find a chimp picture, but apparently it’s even more obvious there), thinness of skull bones, position of orbits under cranial cavity, small teeth, late eruption of teeth, lack of rotation of the big toe, prolonged period of infantile dependency, prolonged period of growth, our long life span, and our large body size (related to retardation of ossification and retention of fetal growth rates).
Okay, so I didn’t come up with that.
It’s well-documented that men are attracted to paedomorphic characteristics in women, for which there are several possible explanations. Given the level of investment by males in their children, it’s obviously a good idea to make sure your kids are your own. One way to do this is by being the first to mate with your mate, and one way to be sure you’re first is by mating young. Perhaps this caused a positive feedback loop of some sort.
Since this holds for most mammals, it’s obviously not the whole story, but it’ll do for now.
Incidentally, there is some evidence for psychological neoteny as well. I could take some cheap shots at the immaturity and mental developmental retardation of Western culture (as Bruce Charlton did—he thought it was a recent phenomenon and blamed education, though; actually, that article tries to equate a midlife crisis with neoteny, though its causes are well-understood and quite different), but the most obvious argument must surely be religion.
A yearning for a heavenly parent figure, who is in firm control of things that are beyond our influence or understanding? This may not describe every religion out there, but it describes the dominant ones, and every religion tends to at least have a comforting element at its core; something to say that, yes, the world makes sense, you just don’t understand it, but “I” (be it the priests or just God himself) have the answer.
This is probably the only thing I agree with Freud on. I’m sure you’ll remember he called religion at its base neurotic and infantile.
It’s all very interesting, and requires more study.