Phylogenetic Relationships (Biomolecules)

Abstract

Biomolecules, in particular DNA, assist us in generating and testing hypotheses about human evolutionary history. Molecular analyses testing for and then utilizing a local molecular clock can inform us as to the timing of the split between different lineages or populations. When applied to the split between hominins and chimpanzees, for instance, the molecular clock estimates of their divergence date place constraints on interpretations of the growing fossil record from the Late Miocene and Early Pliocene. The pattern and distribution of modern human variation can be used to extrapolate back in time to infer when and where the modern human gene pool arose. Mitochondrial DNA and Y chromosome sequences and markers have been extensively surveyed in populations from around the world. Numerous nuclear loci and other markers, such as microsatellites and Alu insertions, have similarly been sampled and analyzed. More recently, high-throughput massively parallel sequencing technologies have allowed for the characterization of hundreds of human and nonhuman primate complete genomes. The majority of such analyses point toward a relatively recent origin for modern human diversity from a small population in Africa within the last 200 Ka, with a subsequent dispersal into Eurasia less than 100 Ka though there is some debate as to the timing of these events. While analyses of ancient mitochondrial sequences from archaic hominins strongly suggest that archaic females did not contribute to the modern human mitochondrial gene pool, whole-genome sequences of two archaic populations suggest limited interbreeding with modern humans in Eurasia but not Africa. Analyses of modern African genomes suggest that some populations also interbred with an as yet unknown archaic population or populations. Thus, while a complete replacement of archaic populations by African-derived modern humans is no longer fully tenable, only a limited amount interbreeding between anatomically modern human populations and archaic forebears is likely to have taken place.