Venom variations
The venom of the Malaya pitviper Calloselasma rhodostoma , collected from Vietnam, Thailand, Malaysia and Java, shows considerable variations in its chemical composition. The pattern of variation is due to the changes in the diet of the snakes in these regions. Since the function of the venom is to immobilise and digest its preys, such diet-dependent variation in the venom's chemical composition appears to be the handiwork of natural selection. Since the changes in the venom may have variable immunological properties, antivenom serums produced by using a mixture of venom from different localities may be more effective.