14 Aug 1995 18:18:31 GMT wrote:

: NE>You say "Humans have children that are less developed than our
: NE>relatives because our brains are so much bigger than our closest
: NE>relatives", but the actual fact is quite different, to whit:
: NE>"Humans can have brains are so much bigger than our closest relatives
: NE>because our have children are born less developed than our relatives".

: NE>You see, the difference in wording is fairly subtle, but the
: NE>difference in meaning is enormous. Your wording says the cause
: NE>of the change is something that the change itself allows; this
: NE>would mean that the cause is something from the future, which you
: NE>can easily see is impossible.

: NE>Jim Moore (

: Let me see if I can state this the way I understand, albeit not in
: technical language:

: The female in the group with the slightly larger head and the slightly
: larger brain is presumably slightly more intelligent and thus more
: successful in rearing offspring, and she passes those genetic traits on
: to her numerous daughters and granddaughters, and to her male progeny
: also. The problem is that the greatgranddaughters have a problem
: birthing the babies with the increasingly bigger heads. The female in
: that generation with the slightly larger and more flexible pelvis will
: be more successful, as will the female who tends to deliver just
: slightly more premature or immature infants (but has the intelligence to
: care for them well). So there are (at least) three tendencies
: cooperating in this particular process of natural selection, and the
: female with the tendency for the best combination of all three will be
: the most successful in producing and rearing viable progeny. Larger
: brain cases, wider and more flexible pelvic girdles, and immature
: infants all advance together as evolutionary trends.

: Does this make sense to y'all?

Correct, which means the three characteristics are correlated. No more
than one of the three characteristics can be used to induct phylogeny.
The large brain probably reflects entry into the treeless savannah.
Adaption to living in that environment also probably led to reduced sexual
dimorphism, loss of tree-climbing features, the initial appearence of the
pair bond, secondaru sexual characteristics rudimentary speech (originally
developed as representational behavior similar to bee dancing) and
increased complexity of social behavior.

Harry Erwin
Home Page: (try a couple of times)
PhD student in comp neurosci: "Glitches happen" & "Meaning is emotional"