Fig. 3.

Variability at first, second, and third codon position sites showing nucleotide changes on the human–chimpanzee stem, the chimpanzee-terminal branch, and the human-terminal branch. Such variability is estimated for each of the three branches by the ratio: number of changes throughout the full tree at those sites showing nucleotide changes on that branch/number of nucleotide changes on that branch. The dataset used to construct the MP tree for the six extant taxa consisted of concatenated coding sequences from 45 genes. Chimpanzee- and human-terminal branches were represented by all 45 genes. Each of the remaining taxa had a minimum of missing sequence data.