"Lane Lewis"  wrote in
message news:bmn9q0$kg4$1{at}darwin.ediacara.org...
>
> "Wirt Atmar"  wrote in message
> news:bmilro$2e88$1{at}darwin.ediacara.org...
> > Trantis asks:
> >
> > >Why did animals develop two Kidneys and two
testicles/ovaries?
> >
> > Once evolution has settled on a bilaterally symmetric
design plan during
> > embryogenesis, duplicating any structure simultaneously
on each side of
> the
> > midline is probably the simplest design possible. The
same question could
> be
> > asked of why do we have two eyes, two ears, two arms,
two lungs, two brain
> > lobes or two nares?
> >
> > The more difficult question to answer is why do we have
only one heart,
> one
> > liver, one pancreas, one stomach, one gut, each
asymmetrically placed
> against
> > the midline?
> >
> > Wirt Atmar
> >
>
> Perhaps those organs that were close to the center did not
need to have a
> double but those out side the center needed two to be
symmetrical. The
> doubling of organs might not be needed for survival just
symmetry. It may be
> just easier to produce. The one organ that might bring
this down is the
> brain which even though is along the center has two
complete sides.
>
> Lane

Perhaps an even deeper question that might be asked is, why
are all larger animals bilaterally symetric, rather than
symetric from front to back, or even "tetra-symetric?" The
latter should have even greater survival value (other things
being equal. :))   ...tonyC
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