gilmour (gilmour at interlynx.net) wrote:
:: One of the reasons often quoted for the limit on human brain size, is the
: restriction placed on head size due to childbirth. In bipedal humans,
: childbirth poses a serious risk for both mother and child (mortality rates
: increasing for both), because the newborn must now pass out of a narrow
: birth canal between the narrower pelvis hips (which have evolved for an
The risk is not determined by a simplisitc "narrowness of the
hips". The problem is due to the largeness of the ischial
tuberosities, FYI.
: larger brains must now be explained as being very significant in order to
Is a larger brain an evolitionary trait?
Larger brains do not correlate with higher IQ.
eg. Neanderthals had huge brains.
: overcome this reverse trend which would have been expected.
:: I would now like to suggest an alternate hypothesis, which is, that larger
: brains are a direct result of bipedalism and difficult child birth rather
: than the opposite.
:: Let me explain.
: Because of bipedalism and its associated difficult childbirth, evolution
You fail to mention the accomodations the mother's body makes
though. What about the softening and separation of the pubic symphysis?
: has come up with a partial solution for the big head problem, (neoteny
: being one), and also a softer, (less rigid) more plastic or malleable skull
: during childbirth.
Yeah. There is a rubbery consistency. this is why bones in
children are difficult to break.
Humans at birth have not only a hole in the top of the
: skull
It's not a "hole", it is a fontanel.
but also the skull cap is extremely soft with radial unhealed
: fractures running in all directions.
Fractures?
Um, why are they called sutures then?
Cheers,
emma
:)