The Context of Human Genetic Evolution

Abstract

The debate on modern human origins has often focused on the relationship between genes and fossils. Although more and more genetic evidence has been accumulating in favor of a recent African origin for modern humans, it has been assumed by many that the fossil evidence remains ambiguous. On the contrary, it has been clear for some time that the fossil evidence does not support the multiregional model: Fossils and archeology indicate a pattern of multiple dispersals from and beyond Africa, against which the genetic data can be compared. The continuing value of paleobiology is in complementing genetic information by revealing the context of human evolution: locating the dispersals and extinctions of populations in time and space, correlating these events with the environmental forces that shaped them, and providing an increasingly detailed understanding of the morphology and technology of early humans.Molecular biology has revolutionized the study of human evolution. The importance of fossils as the primary source of information about our past has been steadily undermined as it has become possible to infer detailed aspects of recent human history from the distribution and frequency of genes found around the world today. To some extent, a fusion of paleontological and genetic approaches came about last year with the extraction and sequencing of ancient DNA from an extinct hominid, the Neanderthal type specimen (Krings et al. 1997), but this is likely to remain a rarity. Ancient DNA, however, has been able to confirm that humans and Neanderthals belonged to different populations over the last quarter of a million years and that Neanderthals did become effectively extinct.These results fit in with an increasingly consistent interpretation of human evolutionary genetics. Compared with chimpanzees and other apes, the human population is relatively lacking in genetic diversity (Ruvolo et al. 1993); such genetic variation as does exist occurs primarily within populations rather than between (Relethford and Harpending 1994); African populations are more diverse genetically than those found anywhere else in the world (Vigilant et al. 1991;Cavalli-Sforza et al. 1994;Watson et al. 1997); and for the most part, non-African patterns of genetic variation can be treated as a subset of African ones. The chronological and demographic context of the processes of diversification has been strongly disputed, but several genetic systems indicate that living populations derive from a relatively small population (effective population size between 5000 and 50,000 individuals) (Rogers and

The phylogeography of Y chromosome binary haplotypes and the origins of modern human populations

“…The uniparentally inherited non-recombining haploid mtDNA and the Y chromosome loci are particularly sensitive to the influences of drift, especially founder effect. Consequently these loci are ideal for assessing the origins of contemporary population diversity, and provide context for paleontological hypothesis testing (Foley, 1998). The combination of a recent molecular age , and geographical structure, makes the NRY a sensitive genetic index capable of tracing the microevolutionary patterns of novel modern human diversity.…”

Origin and primary dispersal of the Mycobacterium tuberculosis Beijing genotype: Clues from human phylogeography

“…The uniparentally inherited nonrecombining haploid mtDNA and the Y chromosome loci are particularly sensitive to the influences of drift, especially founder effect. Consequently these loci are suitable for assessing the origins of contemporary population diversity and provide context for paleontological hypothesis testing (Foley 1998). The mutation rate of the maternally transmitted mitochondrial genome is ∼10 times higher than that of nuclear DNA, which provides abundance of polymorphic sites but creates difficulties in reconstructing genealogies owing to repeated and reverse mutations.…”

Genomic Evidence for an African Expansion of Anatomically Modern Humans by a Southern Route

“…Under the out-of-Africa, or Replacement, model (Foley 1998;Tattersall 2009) the expanding Africans replaced all the archaic human forms encountered in the process. Conversely, in the initial formulations of the multiregional model (Wolpoff et al 1988), populations of anatomically archaic humans were regarded as directly ancestral to the modern populations of the same regions (Wolpoff et al 1988).…”