Evaluating refugia in recent human evolution in Africa

Abstract

Homo sapiens have adapted to an incredible diversity of habitats around the globe. This capacity to adapt to different landscapes is clearly expressed within Africa, with Late Pleistocene Homo sapiens populations occupying savannahs, woodlands, coastlines and mountainous terrain. As the only area of the world where Homo sapiens have clearly persisted through multiple glacial-interglacial cycles, Africa is the only continent where classic refugia models can be formulated and tested to examine and describe changing patterns of past distributions and human phylogeographies. The potential role of refugia has frequently been acknowledged in the Late Pleistocene palaeoanthropological literature, yet explicit identification of potential refugia has been limited by the patchy nature of palaeoenvironmental and archaeological records, and the low temporal resolution of climate or ecological models. Here, we apply potential climatic thresholds on human habitation, rooted in ethnographic studies, in combination with high-resolution model datasets for precipitation and biome distributions to identify persistent refugia spanning the Late Pleistocene (130–10 ka). We present two alternate models suggesting that between 27% and 66% of Africa may have provided refugia to Late Pleistocene human populations, and examine variability in precipitation, biome and ecotone distributions within these refugial zones. This article is part of the theme issue ‘Tropical forests in the deep human past’.

Tropical forests in the deep human past

“…These results complement the work from Blinkhorn et al . [ 54 ] on the availability of refugia in tropical Africa. Refugia are places that remained stable and habitable through various cycles of climate change (see [ 55 ]).…”

“…As the only continent where H. sapiens have clearly persisted through multiple glacial-interglacial cycles, Africa is a key area where classic refugia models can be formulated and tested. Blinkhorn et al [54] apply climatic thresholds on human habitation, rooted in ethnographic studies, in combination with highresolution model datasets for precipitation and biome distributions to identify persistent refugia spanning the Late Pleistocene (130-10 ka). Remarkably, Blinkhorn and colleagues find that refugia were unlikely to be rare phenomena during the Late Pleistocene, even using conservative estimates.…”

Longstanding behavioural stability in West Africa extends to the Middle Pleistocene at Bargny, coastal Senegal

“…4 ), suggesting local constraints on the scope of climate change. A recent study of human refugia in Africa has highlighted the potential suitability of habitats in Senegal, Gambia and western Mali (referred to hereafter as the Senegambian refugia; Supplementary Information 3 ) to enable persistent occupation throughout the Late Pleistocene based on precipitation thresholds of 248–1403 mm, based on ethnographic analogies 68 and corroborated by recent examination of the eastern African MSA record 69 . The distribution of this proposed refugia is consistent with the distribution and chronology of previously known MSA occupations in western Africa.…”

“…3.1 ). This refugia appears to be dominated by tropical xerophytic shrubland habitats with limited connectivity to other, more ecologically diverse refugia (such as in northern, eastern or southern Africa 68 . The lack of longstanding connectivity across the region is consistent with genetic studies of contemporary populations in western Africa 70 , which emphasizes extended phases of isolation from other populations and notable archaic introgression.…”

A spatiotemporally explicit paleoenvironmental framework for the Middle Stone Age of eastern Africa

“…Moreover, Lake Victoria, which is relatively young but estimated to exist by 500–400 kya 45 , is the source of the White Nile, and therefore its refugial position could also have interesting implications for dispersals from the region out of the continent 46 . Together, this highlights the potential role of refugia in structuring MSA cultural and biological diversity 3 , 4 , laying the critical foundations for later human evolution, with microhabitat variability in refugial zones likely being a key component in creating resource-rich landscapes 32 , 47 .…”