There are two ways of working out the phylogeny (family tree) of living animals. One is by analyzing their genes; the other is to analyze the extent to which they are similar in form. In either case. the results can then be integrated with the fossil record. In principle, the two approaches should be complementary. Both should lead to a consistent account of how snake and lizard families descended from a single stem. More or less a greater number of shared traits would mean they recently diverged from a common ancestor.