Determining genetic relationships among the various kinds of advanced snakes is a most difficult and challenging problem. The greatly simplified body plan of snakes offers few anatomical characters that can be used to distinguish among them, and in many cases two or more species have developed the same sets of anatomical characteristics independently. The past reliance on anatomical characteristics has, therefore, provided little in the way of reliable information about snake relationships. To rectify this, it is proposed that the DNA sequences of two mitochondrial genes be obtained from representatives of the eight largest presumptive groups of advanced snakes and, for comparative purposes, from two primitive snake groups. DNA sequence comparisons offer two huge advantages over anatomical comparisons for these studies. One is that the reduction in anatomical complexity is not reflected at the DNA level; the full range of DNA sequence complexity is present for use in determining relationships. The other is that, unlike the case with many anatomical changes, there is almost no possibility that the same sequence changes will occur independently in two different species; thus, with functional convergences from those due to genealogical inheritance. An accurate knowledge of the genetic relationships among advanced snakes is required for understanding the ways in which suites of characteristics develop. For example, knowing exactly how non-poisonous and poisonous snakes are related will resolve some of the controversies that presently surround the development of venom glands and the anatomical components for delivering venom. This knowledge will also provide the foundation for future studies of relationships among snake groups not examined here.
