PATTERN AND TIMING OF EVOLUTIONARY DIVERGENCES AMONG HOMINOIDS BASED ON ANALYSES OF COMPLETE MTDNAS

We have examined and dated primate divergences by applying a newly est ablished molecular/paleontological reference, the evolutionary separat ion between artiodactyls and cetaceans anchored at 60 million years be fore present (MYBP). Owing to the morphological transformations coinci ding with the transition from terrestrial to aquatic (marine) life and the large body size of the animals (which makes their fossils easier to fmd), this reference can be defined, paleontologically, within much narrower time limits compared to any local primate calibration marker hitherto applied for dating hominoid divergences. Application of the artiodactyl/cetacean reference (A/C-60) suggests that hominoid diverge nces took place much earlier than has been concluded previously. Accor ding to a homogenous-rate model of sequence evolution, the primary hom inoid divergence, i.e., that between the families Hylobatidae (gibbons ) and Hominidae, was dated at approximate to 36 MYBP. The correspondin g dating for the divergence between Pongo (orangutan) and Gorilla-Pan (chimpanzee) -Homo is approximate to 24.5 MYBP, that for Gorilla vs Ho me-Pan is approximate to 18 MYBP, and that for Homo vs Pan approximate to 13.5 MYBP. The split between Sumatran and Bornean orangutans was d ated at approximate to 10.5 MYBP and that between the common and pygmy chimpanzees at approximate to 7 MYBP. Analyses of a single gene (cyto chrome b) suggest that the divergence within the Catarrhini, i.e., bet ween Hominoidea and Old World monkeys (Cercopithecoidea), took place > 40 MYBP; that within the Anthropoidea, i.e., between Catarrhini and Pl atyrrhini (New World monkeys), >60 MYBP; and that between Anthropoidea and Prosimii (lemur), approximate to 80 MYBP. These separation times are about two times more ancient than those applied previously as refe rences for the dating of hominoid divergences. The present findings au tomatically imply a much slower evolution in hominoid DNA (both mitoch ondrial and nuclear) than commonly recognized.