Strydom, D. J. (National Chemical Research Laboratory, Council for Scientific and Industrial Research, P. O. Box 395, Pretoria, South Africa) 1974. Snake Venom Toxins: The Evolution of some of the Toxins found in Snake Venoms. Syst. Zool. 22:596–608.—A computer program, ALIGN, was developed to test for homology of proteins. This program was used in conjunction with programs previously developed, to set up phylogenetic relationships and ancestral amino acid sequences for 43 snake venom toxins. From these and other studies emerged two mutually exclusive postulates for the evolution of snake venom toxins from digestive tract enzymes. Internal repitition in the sequence of toxins and homology of toxins with various enzymes were found. Evidence seems to favour one of the above postulates to a slight extent above the other. According to this it seems as if the short neurotoxins evolved from digestive tract enzymes like, for example, ribonuclease and that the cytotoxins and long neurotoxins evolved from the short neurotoxins. Other toxins have developed from, for example, trypsin inhibitors. The concepts of Darwinian and non-Darwinian evolution are both used to explain the evolution of the protein-toxins in snake venoms.