Evolution of poisonous vs. non-poisonous snakes

Open question : " I can understand Natural Selection as well as mutation through cosmic ray DNA damage/modification. My problem is both of the above mechanisms seem predominately subtractive ( but certainly not always).Evolution in general is a gradual process of modification right?Can someone explain why some snakes are not poisonous while others have a most elaborate tool box with behavioral procedures for target identification et. al. Although not a philosophical question, I just have trouble surmising a simultaneous evolution of all the subsystems as well as why would some snakes have this capability and lose it. It would always be useful for enhanced species proppagation, would it not?Edited by Adminnemooseus, : Add a couple of blank lines.Edited by Adminnemooseus, : Changed topic title from "mechanisms of evolution" to "Evolution of poisonous vs. non-poisonous snakes"

Thread copied here from the Evolution of poisonous vs. non-poisonous snakes thread in the Proposed New Topics forum.