Abstract
The evolution of modern humans was a complex process, involving major changes in levels of diversity through time. The fossils and stone tools that record the spatial distribution of our species in the past form the backbone of our evolutionary history, and one that allows us to explore the different processes—cultural and biological—that acted to shape the evolution of different populations in the face of major climate change. Those processes created a complex palimpsest of similarities and differences, with outcomes that were at times accelerated by sharp demographic and geographical fluctuations. The result is that the population ancestral to all modern humans did not look or behave like people alive today. This has generated questions regarding the evolution of human universal characters, as well as the nature and timing of major evolutionary events in the history of Homo sapiens. The paucity of African fossils remains a serious stumbling block for exploring some of these issues. However, fossil and archaeological discoveries increasingly clarify important aspects of our past, while breakthroughs from genomics and palaeogenomics have revealed aspects of the demography of Late Quaternary Eurasian hominin groups and their interactions, as well as those between foragers and farmers. This paper explores the nature and timing of key moments in the evolution of human diversity, moments in which population collapse followed by differential expansion of groups set the conditions for transitional periods. Five transitions are identified (i) at the origins of the species, 240–200 ka; (ii) at the time of the first major expansions, 130–100 ka; (iii) during a period of dispersals, 70–50 ka; (iv) across a phase of local/regional structuring of diversity, 45–25 ka; and (v) during a phase of significant extinction of hunter–gatherer diversity and expansion of particular groups, such as farmers and later societies (the Holocene Filter), 15–0 ka.This article is part of the themed issue ‘Major transitions in human evolution’.
Highlights
Questions about the origins of modern human diversity, the diversity observed among living people and their unique ancestors, are as old as the discipline of Anthropology
Evolutionary models sought answers in the regional differences in Pleistocene hominin morphology to account for contemporary differences among human groups [1,2]
Morphological and genetic research since the late 1980s established that all humans are more closely related to each other than to any Late Quaternary hominin group
Summary
Questions about the origins of modern human diversity, the diversity observed among living people and their unique ancestors, are as old as the discipline of Anthropology. The 200 000-year-old history of the species remains only patchily known, with a poorly mapped African origin, and shaped by major geographical and demographic expansions after 130 ka, when modern human populations began to disperse first across Africa and later into Eurasia [16,17]. This critical change in population dynamics from a demographically small and geographically localized lineage to an expansive migratory one is one of the keys to understanding the mechanisms that underpin the evolution of human diversity. This paper proposes five periods of transition in the evolutionary history of our species, and explores their consequences on levels of diversity
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