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The shaping of human diversity: filters, boundaries and transitions

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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’.

No MeSH data available.


(a) Cartoon of the complex phylogenetic pattern through time, shaped by repeated expansions, extinctions and assimilations; (b) geographical expression of a complex phylogenetic pattern in the fossil and archaeological records; (c) distribution of key fossil specimens and archaeological sites in Africa between 400 and 130 ka in the context of climate change. In (c), blue lines represent fossils of Homo heidelbergensis, purple lines and circles fossils of Homo helmei and red lines and circles fossils of Homo sapiens. Archaeological sites are represented by black squares, Acheulean industries by a hand-axe, and Middle Stone Age industries by a Levallois point.
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RSTB20150241F2: (a) Cartoon of the complex phylogenetic pattern through time, shaped by repeated expansions, extinctions and assimilations; (b) geographical expression of a complex phylogenetic pattern in the fossil and archaeological records; (c) distribution of key fossil specimens and archaeological sites in Africa between 400 and 130 ka in the context of climate change. In (c), blue lines represent fossils of Homo heidelbergensis, purple lines and circles fossils of Homo helmei and red lines and circles fossils of Homo sapiens. Archaeological sites are represented by black squares, Acheulean industries by a hand-axe, and Middle Stone Age industries by a Levallois point.

Mentions: The archaeological record of modern human origins is complex. All early modern human fossils have been found in association with Middle Stone Age (MSA) lithic traditions, but the MSA pre-dates the earliest known fossils of H. sapiens [53]. Furthermore, the modern human fossils of Herto were found in the context of an archaeological industry that has both MSA and Acheulean elements [54], while at the similarly dated site of Pinnacle Point in South Africa, behavioural innovations interpreted as reflecting the more complex cognition of modern humans are observed [51]. The complexities of the archaeological and (scant) fossil record of the period 300–130 ka in Africa suggest a prolonged phase in which repeated expansions and contractions would have led to the recurrent assimilation within a single lineage of biological and behavioural novelties acquired locally during periods of allopatry (figure 2).Figure 2.


The shaping of human diversity: filters, boundaries and transitions
(a) Cartoon of the complex phylogenetic pattern through time, shaped by repeated expansions, extinctions and assimilations; (b) geographical expression of a complex phylogenetic pattern in the fossil and archaeological records; (c) distribution of key fossil specimens and archaeological sites in Africa between 400 and 130 ka in the context of climate change. In (c), blue lines represent fossils of Homo heidelbergensis, purple lines and circles fossils of Homo helmei and red lines and circles fossils of Homo sapiens. Archaeological sites are represented by black squares, Acheulean industries by a hand-axe, and Middle Stone Age industries by a Levallois point.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4920297&req=5

RSTB20150241F2: (a) Cartoon of the complex phylogenetic pattern through time, shaped by repeated expansions, extinctions and assimilations; (b) geographical expression of a complex phylogenetic pattern in the fossil and archaeological records; (c) distribution of key fossil specimens and archaeological sites in Africa between 400 and 130 ka in the context of climate change. In (c), blue lines represent fossils of Homo heidelbergensis, purple lines and circles fossils of Homo helmei and red lines and circles fossils of Homo sapiens. Archaeological sites are represented by black squares, Acheulean industries by a hand-axe, and Middle Stone Age industries by a Levallois point.
Mentions: The archaeological record of modern human origins is complex. All early modern human fossils have been found in association with Middle Stone Age (MSA) lithic traditions, but the MSA pre-dates the earliest known fossils of H. sapiens [53]. Furthermore, the modern human fossils of Herto were found in the context of an archaeological industry that has both MSA and Acheulean elements [54], while at the similarly dated site of Pinnacle Point in South Africa, behavioural innovations interpreted as reflecting the more complex cognition of modern humans are observed [51]. The complexities of the archaeological and (scant) fossil record of the period 300–130 ka in Africa suggest a prolonged phase in which repeated expansions and contractions would have led to the recurrent assimilation within a single lineage of biological and behavioural novelties acquired locally during periods of allopatry (figure 2).Figure 2.

View Article: PubMed Central - PubMed

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’.

No MeSH data available.