The type of maturation that occurs in the human brain in the first
nine months post-natal is of the same variety that is occuring late
pre-natal in other parts of the human. Humans develop locomotion and
social signalling (language) post-natal. Their visual system, though
fed with an essentially mature data stream from the eyes, is incapable
at birth of sifting through the jumble of visual data except for the
crudest identification tasks. These are all areas where other
mammalian species are born with refined capabilities at birth: a foal,
for example, is able within an hour or so post-natal to run and
respond to signals from others of its species, and recognize and
respond to danger.
Nutritional or toxic interruption of in utero development results in a
variety of non-reversible abnormalities. In the same way, the
"environmental diet" of the newborn is critical, and impoverishment in
various ways can result in the mental equivalent of truncated limbs.
Of course, post-natal nutrition and hygiene are also important!
The industrialized world follows an admirable set of accepted
procedures for pre- and post-natal nutrition, and post-natal hygiene.
Unfortunately, the environmental diet most children in the modern
industrialized world are offered is not so admirable, and in fact the
supposed dictate of hygiene are often at odds with a healthy
environmental diet. There are many exceptions to each of these
generalizations, of course.