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In the Light of Evolution Volume IV: The Human Condition
changes (in expression profiles as well as protein-coding sequences) that might mechanistically underlie the evolution of such distinctive human features as expanded cognitive ability, sociality, and language. The authors illustrate this phylogenomic approach by recent work that implicates particular loci in the adaptive evolution of high levels of aerobic energy metabolism that a large mammalian brain necessitates.
In Chapter 4, Angela Hancock and several other authors associated with the laboratory of Anna Di Rienzo extend this general phylogenomic perspective to analyze genome-wide scans of SNPs (single-nucleotide polymorphisms) in numerous human populations representing distinct ecoregions on planet Earth, or that differ in fundamental subsistence mode with respect to diet. In principle, genetic variation among geographic populations might register adaptive differences promoted by environmental selection, or historical population-demographic effects that are mostly independent of the ecological selective regime per se. Hancock and her coauthors attempt to distinguish these two classes of historical causation by searching for consistent distributions of SNPs vis-à-vis human diet and ecoregion, after applying analytical methods designed to control for gene-environment associations that might be due to historical population demography. The authors conclude that strong signals of natural selection related to diet and climate exist for SNPs at particular genes that are centrally involved in carbohydrate utilization and energy metabolism. The authors also compare their phylogenomic approach and findings to those of previous genome-wide association studies in humans.
Africa is humanity’s evolutionary cradle, and its contemporary populations retain extraordinary genetic and linguistic diversity that offers anthropologists a wellspring of biological and cultural information about human history on that continent over the past 200 millennia. For example, with respect to languages, researchers recognize more than 2,000 ethnolinguistic groups that can be classified into four major African language families; and with respect to genetic lineages, mitochondrial (mt) DNA (which is inherited maternally) and the Y chromosome (which is transmitted paternally) both display higher genealogical diversity and evolutionary depth in Africa than in many other regions of the planet combined (as might be expected under a model of African ancestry for all modern humans). In Chapter 5, Laura Scheinfeldt, Sameer Soi, and Sarah Tishkoff address the demographic history of human populations in Africa by compiling and comparing scientific information from archaeology (including cultural artifacts), comparative linguistics, and molecular genetics. Their synthesis reveals various signatures of past population movements on the continent, sometimes registered in particular genetic markers (either neutral or under selection), sometimes registered in cultural practices (such as agriculture and pastoralism), sometimes relatable to geophysical changes