Molecular phylogeny of the hominoids: inferences from multiple independent DNA sequence data sets |
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Authors: | Ruvolo M |
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Institution: | Department of Anthropology, Harvard University, Cambridge, Massachusetts 02138, USA. ruvolo@fas.harvard.edu |
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Abstract: | Consensus on the evolutionary relationships of humans, chimpanzees, and
gorillas has not been reached, despite the existence of a number of DNA
sequence data sets relating to the phylogeny, partly because not all gene
trees from these data sets agree. However, given the well-known phenomenon
of gene tree-species tree mismatch, agreement among gene trees is not
expected. A majority of gene trees from available DNA sequence data support
one hypothesis, but is this evidence sufficient for statistical confidence
in the majority hypothesis? All available DNA sequence data sets showing
phylogenetic resolution among the hominoids are grouped according to
genetic linkage of their corresponding genes to form independent data sets.
Of the 14 independent data sets defined in this way, 11 support a human-
chimpanzee clade, 2 support a chimpanzee-gorilla clade, and one supports a
human-gorilla clade. The hypothesis of a trichotomous speciation event
leading to Homo; Pan, and Gorilla can be firmly rejected on the basis of
this data set distribution. The multiple-locus test (Wu 1991), which
evaluates hypotheses using gene tree-species tree mismatch probabilities in
a likelihood ratio test, favors the phylogeny with a Homo-Pan clade and
rejects the other alternatives with a P value of 0.002. When the
probabilities are modified to reflect effective population size differences
among different types of genetic loci, the observed data set distribution
is even more likely under the Homo-Pan clade hypothesis. Maximum-likelihood
estimates for the time between successive hominoid divergences are in the
range of 300,000-2,800,000 years, based on a reasonable range of estimates
for long-term hominoid effective population size and for generation time.
The implication of the multiple-locus test is that existing DNA sequence
data sets provide overwhelming and sufficient support for a
human-chimpanzee clade: no additional DNA data sets need to be generated
for the purpose of estimating hominoid phylogeny. Because DNA hybridization
evidence (Caccone and Powell 1989) also supports a Homo-Pan clade, the
problem of hominoid phylogeny can be confidently considered solved.
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