"Representative Trantis"  wrote in
news:blf5do$1sk1$1{at}darwin.ediacara.org: 

> 
> "TomHendricks474"  wrote in message
> news:blad18$l4s$1{at}darwin.ediacara.org...
>> << This something (I finally get to the point) is that it seems clear
>> that bipedalism evolved first, and that the intelligence developed
>> later, 
> having
>> to simply make do with what it has, ie, an inadequatly narrow pelvis
>> for such a large brain/skull.
>>
>> For me this seems to stare you in the face. Why wasn't this picked up
>> upon much earlier? (Or am I missing something about the specifics of
>> the anatomical requirements of bipedalism in apes/humans? )

>> I think the helplessness of the newborn is a selected advantage,
>> because 
> it
>> allows brain development under the tutelage and support of the mother
>> and social group.
>> Thus a genetic set plan, is replaced by a genetic + cultural
>> evolution 
> plan
>> which is an improvement for building intelligence.

 
> Well, yes, but you can't escape the fact tat humans are
> underdeveloped. It seems a very dangerous thing to evolve a system
> which leaves a newborn human helpless, unless it's unavoidable.
 
> According to Richard Leakey, in his book 'The Origin Of Humankind',
> Chapter 3, states.
 
> "The helplessness of newborn human infants is, however, less a
> cultural adaption than a biological necessity. Human infants come into
> the world too early, a consequence of our large brain and the
> engineering constraints of the human pelvis...... A simple calculation
> besed on comparisons with other primates reveals the gestation length
> in Homo sapiens, whose averagebrain capacity is 1350 cubic
> centimeters, should be twenty-one months, not the nine months it
> actually is. Human infants therefore have a year's growth to catch up
> on when they are born, hence their helplessness." 

While increase in brain size may well have exceeded the ability of the 
pelvis to adapt, I think Tom has a good point. Development of the myelin 
sheath on neurons takes over a year in human infants, during which period 
considerable changes take place in neuronal connections in the brain, 
probably in response to environmental stimuli, especially exposure to 
language (note the specialized nature of "baby talk"). So even with 
larger hips the gestation period might not be lengthened all that much, 
and babies would still be helpless at birth.


In fact it may be that walking upright allowed, rather than required, 
babies to be born helpless, as the mother could then carry them rather 
than the infants having to have some ability to hang on to the mother.

Yours,

Bill Morse
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