Ask A Scientist Zoology Archive

name         Kim R.
status       educator
age          40s

Question -
I have been asked by a student, "How did the venomous snakes evolve? Why
did some snakes become venomous and other not for instance, a garter snake
and a rattler." I do know that some are constrictors and did not have the
need for a toxic venom, but that does not account for the differences
between vipers and a non-poisonous snake.
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I hope you get a more specific reply from someone who knows more about
snakes than I do, but my stock reply to questions of "why" things happen in
nature is, "because it works." Evolution is a somewhat random process of
mutation and adaptation, and if something happens that works it will then be
selected for and enhanced. If a mutation improves survival chances then it
will be selected for in future generations, if not, it will disappear.

J. Elliott
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Venomous snakes are predators seeking fast moving prey, usually mammals.
They have evolved because their niche includes chasing their food.  Snakes can not 
move very fast so the ambush and strike will allow the snake to eventually catch up 
to the previously faster moving but now dead prey.  These snakes use their tongues 
to sense the heat trail produced by the warm blooded mammal.  
Garter snakes and the like have 
it easier in that their prey are slow to move in the first place, such as 
insects, etc.  It would be a waste to be posionous when you don't need it.  
Evolution has fine tuned all existing organisms, so snakes are the way they 
are because it works.  Natural selection is a powerful force, but effective 
in developing the best species.

Steve Sample
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