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Australian Eastern tiger snake Source: Wikipedia |
Venomous snakes make interesting subjects for study in that they represent an example of a complex evolutionary arms race which can be traced in their venom. This is often a complex mixture of related but subtly different chemicals, often coded for by genes which are themselves subtly different versions of one another.
The arms race is due to snakes usually preying on a range of prey species, each of which has selection pressure to evolve resistance to the snakes venom. But, if the snake merely responded to one prey's resistance by changing it's venom, this might be less effective against another of its prey species, so there is evolutionary pressure on the snake to retain it's 'older' venom but supplement it with a newer version as well. This occurs by gene duplication, then mutation of the 'spare' copy.