Human Genetic Diversity and its History

Abstract

Aspects of the evolutionary and historical processes that shaped present-day human diversity can be inferred from patterns of genetic variation within and between populations. The main questions currently being addressed include the evolutionary relationships among contemporary humans and the different human forms documented in the fossil record, the extent and causes of the genetic differences among modern populations, and the implications of such differences for applied research in fields such as medical genetics, pharmacogenetics, and forensic science. In this chapter, we outline the main current models of human evolution and review the available ancient and modern DNA evidence in the light of these models. We suggest that, despite ongoing controversy, most data are easier to reconcile with a model in which the ancestors of modern populations dispersed recently (<200 000 years ago) from Africa and essentially or completely replaced previously settled human forms. However, it has become increasingly evident that models assuming the expansion of a small African group are oversimplified, and more complex scenarios need be envisaged, including genetic substructuring in the expanding population. How much substructure is needed to explain existing data is unclear, and whether this apparent substructure could be partly due to admixture between modern and archaic humans is debated. The available studies among modern populations show that the differences tend to be patterned in geographical space, but that variation tends to be continuous and strong genetic boundaries rarely occur, suggesting a major role of isolation by distance in shaping human diversity. As a consequence, global human diversity is not well described by a small set of well-defined races. The extent to which racial classifications might be useful in some applications remains to be demonstrated. Throughout the chapter, we emphasise the large amount of uncertainty surrounding the interpretation of genetic data, when they are used either to make inferences on our origins or to predict disease risk.

STR-based genetic structure of the Berber population of Bejaia (Northern Algeria) and its relationships to various ethnic groups

“…They cannot be seen as a reliable representation of the relationships between populations due to the fact that such trees ignore the existence of gene flow, which is a crucial feature of human populations (Barbujani and Chikhi, 2007).…”

KLFDAPC: A Supervised Machine Learning Approach for Spatial Genetic Structure Analysis

“…The genetic differentiation and substructure of human populations are impacted by spatially heterogeneous landscapes (Barbujani and Excoffier 1999; Manica, et al 2005), social stratification (Parsons 1966; Labonte, et al 2005), as well as culture (Root 2000). For a long time, an interesting debate in population genetics is whether continuous clines or discrete clusters can better characterize human genetic variation (Serre and Pääbo 2004; Rosenberg, et al 2005; Frantz, et al 2009; Perez, et al 2018).…”

“…The genetic differentiation and substructure of human populations are impacted by spatially heterogeneous landscapes [1, 2], social stratification [3, 4], as well as culture [5]. For a long time, an interesting debate in population genetics is whether continuous clines or discrete clusters can better characterize human genetic variation [6–9].…”