IUBio

Big Brains

Emma Chase VanCott 7elc at qlink.queensu.ca
Mon Apr 13 20:17:44 EST 1998


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
:)






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