On Mon, 21 Jul 2003 23:37:20 +0000 (UTC), Jan Philips
 wrote:

>On Sun, 20 Jul 2003 22:24:09 +0000 (UTC), wkutrent{at}yahoo.com (Trent
>Smith) wrote:
>
>>Well, think of it this way.  I teach in genetics that there is a
>>stabilizing selection that keeps human head sizes at birth in check. 
>>Head too small--child is at an obvious disadvantage.  Head is too
>>big--he or she can't pass through the birth canal...but wait, haven't
>>we all but eliminated that second selective pressure by the widespread
>>use of C-sections?  I predict that head sizes at birth will increase
>>(if in fact the initial statement about the reasons for the stability
>>were true.)
>
>Could we get to the point were every baby's head is too large to be
>born vaginally?
>

How many babies are born all around the world each year?
What percentage are delivered by C-section?

I don't think that this type of medical intervention (or high-tech
genetic engineering or whatever) is likely to make any significant
impact on human evolution for a long time to come.   When significant
numbers of people are impacted, as by massive public health measures,
then that is another story.
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