A practical method for calculating evolutionary trees from sequence data.

In a previous paper (Klotz et a1., 1979) we described a method for determining evolutionary trees from sequence data when rates of evolution of the sequences might differ greatly. It was shown theoretically that the method always gave the correct topology and root when the exact number of mutation differences between sequences and from their common ancestor was known. However, the method is impractical to use in most situations because it requires some knowledge of the ancestor. In this present paper we describe another method, related to the previous one, in which a present-day sequence can serve temporarily as an ancestor for purposes of determining the evolutionary tree regardless of the rates of evolution of the sequences involved. This new method can be carried out with high precision without the aid of a computer, and it does not increase in difficulty rapidly as the number of sequences involved in the study increases, unlike other methods.