Tag: Out of Africa

Our article on how a huge expansion of the human niche in Africa around 70,000 years ago likely equipped later out-of-Africa dispersals with unique ecological flexibility is now published in Nature.

Emily Y. Hallett, Michela Leonardi, Jacopo Niccolò Cerasoni, Manuel Will, Robert Beyer, Mario Krapp, Andrew W. Kandel, Andrea Manica & Eleanor M. L. Scerri
Major expansion in the human niche preceded out of Africa dispersal
Nature

Homo sapiens evolved in Africa starting around 300,000 or 250,000 years ago. Despite having attempted dispersals out of Africa several times during this period, all non-Africans today descend from a single dispersal that happened around 50,000 years ago.

In this article, we reconstruct human ecological dynamics in Africa between 120,000 and 15,000 years ago, using the method we developed for our study on ungulates. We found that humans began to occupy new environments around 70,000 years ago. Because this occurred in quite different habitats at the same time, it is unlikely to be due to a single technological innovation (e.g., for storing and transporting water).

The most likely explanation is that during this period, positive feedback occurred between larger geographical ranges, increased contacts between populations (as also suggested by morphological data), facilitated cultural exchanges, and a higher likelihood of developing and maintaining innovations.

This increased ecological flexibility would have later helped humans successfully disperse out of Africa.

Article

Abstract

All contemporary Eurasians trace most of their ancestry to a small population that dispersed out of Africa about 50,000 years ago (ka)^{1,2,3,4,5,6,7,8,9}. By contrast, fossil evidence attests to earlier migrations out of Africa^{10,11,12,13,14,15}. These lines of evidence can only be reconciled if early dispersals made little to no genetic contribution to the later, major wave. A key question therefore concerns what factors facilitated the successful later dispersal that led to long-term settlement beyond Africa. Here we show that a notable expansion in human niche breadth within Africa precedes this later dispersal. We assembled a pan-African database of chronometrically dated archaeological sites and used species distribution models (SDMs) to quantify changes in the bioclimatic niche over the past 120,000 years. We found that the human niche began to expand substantially from 70 ka and that this expansion was driven by humans increasing their use of diverse habitat types, from forests to arid deserts. Thus, humans dispersing out of Africa after 50 ka were equipped with a distinctive ecological flexibility among hominins as they encountered climatically challenging habitats, providing a key mechanism for their adaptive success.

Media coverage

New York Times: “When Humans Learned to Live Everywhere” by Carl Zimmer
The Independent: “Early humans adapted to extreme habitats. Researchers say it set the stage for global migration“
New Scientist: “70,000 years ago humans underwent a major shift – that’s why we exist” by Michael Marshall
Nature News and Views: “Homo sapiens adapted to diverse habitats before successfully populating Eurasia” by William Banks
Natural History Museum: “Sharing ideas might have helped Homo sapiens adapt for life outside Africa” by James Ashworth
University of Cambridge: “Learning to thrive in diverse African habitats allowed early humans to spread across the world“
IFLScience: “Why Homo Sapiens Failed To Migrate Out Of Africa Until 60,000 Years Ago“
Naked Scientist: “Humanity’s road to dominance began earlier than expected“

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So excited to have contributed to this amazing new preprint!

In this study, we quantified the role of climate and mountains in shaping modern and ancient human genetic diversity.

Genomics shows that contemporary human populations result from the mixing of ancestral groups that are genetically distinct (ancestral genetic lineages) with unknown origins. In theory, ancient DNA could help disentangling their origin, but not in this case because we don’t have enough samples of the right age.

For this reason, we used a different strategy. We explicitly simulated the genetic history of humans in their spread out of Africa testing different values for demographic parameters and physiological responses to the changing climate. By doing so we could see if we can reconstruct the observed genetic diversity (spoiler alert: yes) and which parameters and climate variables shaped it.

For example, we find that aridity is the key factor controlling the timing for the out of Africa and mountains can be huge genetic barriers but only in some areas (e.g. Caucasus and Himalayas, not the Urals).

Thanks to this study, not only we could reconstruct such an important part of our genetic history, but we could also quantify the differential role of climate and topography through space and time in our spread out of Africa.

Preprint

Pierpaolo Maisano Delser, Mario Krapp, Robert Beyer, Eppie R Jones, Eleanor F Miller, Anahit Hovhannisyan, Michelle Parker, Veronika Siska, Maria Teresa Vizzari, Elizabeth J. Pearmain, Ivan Imaz-Rosshandler, Michela Leonardi, Gian Luigi Somma, Jason Hodgson, Eirlys Tysall, Zhe Xue, Lara Cassidy, Daniel G Bradley, Anders Eriksson, Andrea Manica
Climate and mountains shaped human ancestral genetic lineages
bioRxiv 2021.07.13.452067; doi: https://doi.org/10.1101/2021.07.13.452067

Abstract

Extensive sequencing of modern and ancient human genomes has revealed that contemporary populations can be explained as the result of recent mixing of a few distinct ancestral genetic lineages. But the small number of aDNA samples that predate the Last Glacial Maximum means that the origins of these lineages are not well understood. Here, we circumvent the limited sampling by modelling explicitly the effect of climatic changes and terrain on population demography and migrations through time and space, and show that these factors are sufficient to explain the divergence among ancestral lineages. Our reconstructions show that the sharp separation between African and Eurasian lineages is a consequence of only a few limited periods of connectivity through the arid Arabian peninsula, which acted as the gate out of the African continent. The subsequent spread across Eurasia was then mostly shaped by mountain ranges, and to a lesser extent deserts, leading to the split of Europeans and Asians, and the further diversification of these two groups. A high tolerance to cold climates allowed the persistence at high latitudes even during the Last Glacial Maximum, maintaining a pocket in Beringia that led to the later, rapid colonisation of the Americas. The advent of food production was associated with an increase in movement, but mountains and climate have been shown to still play a major role even in this latter period, affecting the mixing of the ancestral lineages that we have shown to be shaped by those two factors in the first place.