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From: krista@ihuxe.UUCP (K.J.Anderson)
Newsgroups: net.bio
Subject: Re: Bipedalism
Message-ID: <1287@ihuxe.UUCP>
Date: Tue, 22-Apr-86 14:28:50 EST
Article-I.D.: ihuxe.1287
Posted: Tue Apr 22 14:28:50 1986
Date-Received: Wed, 23-Apr-86 23:43:04 EST
Distribution: net
Organization: AT&T Bell Laboratories
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<>
   There is another good reason why more mammals have not developed
bipedalism.  Pregnancy is more difficult for the biped.  She
has only 2, not 4, legs to support the extra weight.  Also there is
a horizontal component of force on her spine as well as the vertical
component.  The strain on the biped's back while pregnant is
significant; ask any human mother!  And finally, miscarriage is more
likely since gravity is pulling the fetus against the cervix.
   These factors are irrelevant to reptiles and birds since they lay
eggs.  So now I'm wondering about marsupials, particularly the
kangaroo.  Her joey is born while still an embryo and completes its
development in the pouch.  This would alleviate the miscarriage
problem, but it seems that the mother would still have the leg and
back problems.
   As far as nature is concerned, our lives need not be perfect or
even pleasant - just survivable. 
  This is all musings and conjecture, of course.
              ihnp4!ihuxe!krista
-- 
ihnp4!iham1!krista  oh,i'llgetflamedtheni'llcryoh,dear