Did Our Species Evolve in Subdivided Populations across Africa, and Why Does It Matter?

Abstract

We challenge the view that our species, Homo sapiens, evolved within a single population and/or region of Africa. The chronology and physical diversity of Pleistocene human fossils suggest that morphologically varied populations pertaining to the H. sapiens clade lived throughout Africa. Similarly, the African archaeological record demonstrates the polycentric origin and persistence of regionally distinct Pleistocene material culture in a variety of paleoecological settings. Genetic studies also indicate that present-day population structure within Africa extends to deep times, paralleling a paleoenvironmental record of shifting and fractured habitable zones. We argue that these fields support an emerging view of a highly structured African prehistory that should be considered in human evolutionary inferences, prompting new interpretations, questions, and interdisciplinary research directions.

Keywords: African origins; Middle Stone Age; evolutionary genetics; human evolution; paleoanthropology; paleoecology.

Figure 1

Evolutionary Changes of Braincase Shape from an Elongated to a Globular Shape. The latter evolves within the H. sapiens lineage via an expansion of the cerebellum and bulging of the parietal. (Left) Micro-computerized tomography scan of Jebel Irhoud 1 (∼300 ka, North Africa). (Right) Qafzeh 9 (∼95 ka, the Levant).

Figure 2

Middle Stone Age Cultural Artefacts. (A–D) Bifacial foliates from northern Africa (A, Mugharet el Aliya; B–D, Adrar Bous). (E–G) Bifacial foliates from southern Africa (Blombos Cave). (H,I) Tanged tools from northern Africa. (J) Segmented piece bearing mastic residue from southern Africa (Sibudu). (K) Engraved ochre fragment (Blombos Cave). (L–N) Engraved ostrich eggshell fragments from southern Africa (Diepkloof). (O,P) Bone points from southern Africa (Sibudu and Blombos Cave, respectively). (Q) Bone point from northern Africa (El Mnasra). (R–V) Perforated Trivia gibbosula shells from northern Africa (R,S, Grotte de Pigeons; T–V, Rhafas, Ifri n’Ammar, and Oued Djebbana, respectively). (W–Aa) Perforated Nassarius kraussianus shells from Blombos Cave. (Ab) Conus ebraeus shell bead (Conus 2) from southern Africa (Border Cave). (Ac) Ochre fragment shaped by grinding from southern Africa (Blombos Cave). All scales are 1 cm. Boxed items indicate rescaled artefacts. Images reproduced, with permission, from (A–D, H, I) The Stone Age Institute; (E–G, J–P, Ac) from ; (Q) from ; and (R–Ab) from , , .

Figure I

Simple IBD Model with Cultural Data. Note that similarity can increase with distance under some circumstances, for example when similar habitats are separated by considerable distances, with areas of different habitat types being located between them.

Figure 3

Inferring Population Size Change in Unstructured and Structured Populations For a Figure360 author presentation of Figure 3, see the figure legend at https://doi.org/10.1016/j.tree.2018.05.005 The probability, or expected rate, of coalescence of lineages in a single panmictic population is inversely proportional to the population size at the time. Different panmictic population size histories (A) therefore shape the temporal distribution of coalescent events (B). When estimated for many regions of the genome, the temporal distribution of these nodes can be used to estimate the instantaneous inverse coalescence rate (IICR), which in a single panmictic population is a direct proxy for the population size (C). Software such as the pairwise sequentially Markovian coalescent (PSMC) or the multiple sequentially Markovian coalescent (MSMC) can be used to estimate the IICR/population size change in the past. However, when data are sampled from a structured meta-population consisting of subpopulations connected by migration (D), changes in migration through time, and/or in sampling, can generate any IICR-inferred population size history without any actual change in the meta-population size (N_e).

Figure 4

Middle and Late Pleistocene African Environmental Variability in Space and Time. (Left) Map of Africa with key archaeological and fossil sites discussed in the text. Colored boxes indicate averaged regions for simulated precipitation changes from the transient glacial/interglacial LOVECLIM climate model experiment . (Right) Precipitation changes (%) relative to the long-term 784 thousand year mean in the key regions highlighted in left panel, as simulated by transient 784 thousand year-long LOVECLIM climate model simulation . From top to bottom the regions are eastern equatorial Africa, southern Africa, northwestern Africa, and the central Sahara region.