M. Adam Davis wrote:
> Our eyes converge because they can

You have absolutely no way of knowing that, and in fact it's highly
unlikely.  So very many species, some quite distantly related, have pivoting
eyes.  There clearly was significant selection pressure to maintain this
complex system.  This in turn says that being able to swivel the eyes is a
competitive advantage.  In other words, it's useful.

So let's say it correctly: "Our eyes move because that has survival value".

> the primary reason for eye
> movement to to avoid head movement.  Convergence is simply "icing on
> the cake" - a free tool we can use.

More wild speculation.  You can not say why a feature evolved.  At best you
can say that it appears to have certain advantages currently.  These may be
rather different from those that caused the feature to originally evolve.

It's likely that stereo vision and the resulting better 3D comprehension of
one's surroundings is a survival advantage.  Allowing the eyes to converge
reduces the processing power required for 3D perception and applies the high
resolution area of the image sensor to the subject being observed.

While there is no way to prove that's what caused the selection pressure for
this mechanisms, it is at least a plausible hypothesis.  It is quite
unlikely this is merely a "free tool" that is "icing on the cake".  If it
were, it would very unlikely have been selected for so many different times.
Just about all 2-eyed predators on this planet have significant convergence
between the two images, from animals as distantly related as eagles and
jaguars.  Interestingly, 2-eyed non-predators generally have widely
divergent gazes.  Apparently, 3D perception is important when you're
hunting, but a wide field of view is more important when you're being
hunted.  That kindof makes sense, but again, you can't say for sure that's
why these systems evolved and were maintained.


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