Estimation of hominoid phylogeny from a DNA hybridization data set

Analysis of the expanded data set of Sibley and Ahlquist (1987) on primate phylogeny using a maximum likelihood mixed model analysis of variance method shows that there is significant evidence for resolving the Homo-Pan-Gorilla trifurcation in favor of a Homo-Pan clade. The resulting tree is close to that estimated by Sibley and Ahlquist (1984). The mixed model can be used to test a number of hypotheses about the existence of components of variance and the linearity of the relationship between branch length and expected distance. No evidence is found that there is a variance component for extract, or for the individual from which the extract was taken. A variance component for experiment does seem to exist, presumably arising as a result of error of measurement of the common standard from which all values in the same experiment were subtracted. There is significant evidence that the relationship between total branch length between species and their expected distances is nonlinear, or else that the measurement error on larger distances is greater than on smaller ones. Allowing for the nonlinearity might cause one to infer the time of distant common ancestors as less remote than the measured hybridization values would imply if used directly.