Genetic History of the Human Species

Abstract

A major and continuing issue in anthropology is the recent evolutionary history of the human species. One question is the relationship of early humans ( Homo erectus ) to later larger‐brained hominids often referred to as ‘archaic humans’ and ‘anatomically modern humans’. The major debate is between the recent African origin model and the multiregional model. The recent African origin model proposes that Homo sapiens arose as a separate species in Africa within the past 200 000 years, and then dispersed across the Old World replacing non‐African archaic populations. The multiregional model suggests that human evolution over the past 2 million years has been within a single evolving polytypic species. Genetic data have been used increasingly to address these different models (and different variants of each). Several different approaches have been used: gene trees, genetic diversity within populations, genetic distances between populations, and reconstructions of ancient demography. Much of the genetic data is consistent with a replacement model. However, these data are also compatible with a general multiregional model that postulates genetic input from at least two geographic regions. To date, neither model is supported unequivocally by the genetic evidence. Genetic estimates of ancient population size favor an African origin model, but it is still not clear whether this rules out non‐African archaic genetic input. One possibility is that our species is mostly, but not exclusively, out of Africa.

Genetic Structure Analysis of Three Hispanic Populations from Costa Rica, Mexico, and the Southwestern United States Using Y-Chromosome STR Markers and mtDNA Sequences

“…Mutations sometimes can either make haplotypes identical not due to ancestry, or, conversely, lead to differences between individuals with the same ancestral mtDNA (Relethford 2001). This may influence the distribution of the haplotypes (Cavalli-Sforza 1998).…”

“…Also, we estimated genetic distances for the three populations according to the method of Tamura and Nei (1993) for mtDNA and according to the method of Nei (1972) for Y-chromosome STRs. These methods analyze the average genetic differences between local, regional, and continental populations by computing distances between pairs of populations and then analyzing them to determine how past evolutionary events could explain the patterns of genetic distance observed in presentday populations (Relethford 2001).…”

Human Genetic Diversity and its History

“…Under the Out of Africa (OOA), or Recent African Origin (Howells, 1976;Stringer and Andrews, 1988;Stringer, 1989) or Replacement (e.g. Relethford, 2003) model, present-day populations are regarded as deriving from a major spatial and demographic expansion of African populations of H. sapiens, starting less than 200 KY ago. These populations colonised the whole planet, replacing, essentially with no admixture, previously settled H. erectus and H. neandertalensis populations.…”

“…On the other hand, the Multi-Regional (MR) model posits that Eurasian populations of H. erectus or H. neandertalensis are part of the genealogy of present-day humans (Wolpoff et al, 1988). This means that only one human species existed in the last MY or so, encompassing all these different morphologies, which should then be simply classified as archaic and modern forms of a polytypic H. sapiens species (Relethford, 2003). These basic models really represent the extremes of a range of possible models, whose classification, in turn, is not completely clear (but see Aiello, 1993).…”

Recent developments in genetic data analysis: what can they tell us about human demographic history?

“…Given this perspective, it does not aim to be an exhaustive treatment of the genetic evidence for past human demographic history, which has been well covered recently (Harpending and Rogers, 2000;Relethford, 2001;Goldstein and Chikhi, 2002;CavalliSforza and Feldman, 2003). The motivation behind this review is that the connection between genetic data and demographic history appears rather more complicated than hitherto appreciated, and, as evidence of the widespread effects of selection in the human genome continues to mount Nachman, 2001;Payseur and Nachman, 2002; but see Hellmann et al, 2003), and with increasing concerns of the subtle effects of ascertainment and population structure (Wakeley, 1999;Wakeley et al, 2001;Ptak and Przeworski, 2002), it is from a rigorous model-based perspective that progress may be best made.…”