Did a changing climate cause the extinction of an evolutionary branch of Homo sapiens?

The catch­ment area of the Limpopo River. Here lived an an­cestor of man, Par­anthropus ro­bus­tus about two mil­lion years ago (photo: MARUM – Cen­ter for Mar­ine En­vir­on­mental Sci­ences at the Uni­versity of Bre­men).

So far only little is known about the climate history of the eastern part of the African continent. It is in this region that scientists assume the origins of human evolution took place, which is why it is worth a closer look. The past climate of this region is of vital interest, since it is an important factor in the struggle for life of species.

Between about two million and 900 000 years before present Paranthropus robustus lived in South Africa. It is an extinct evolutionary branch of Homo sapiens. An international team of scientists including James Collins of GFZ Section Geomorphology, and led by the University of Bordeaux, now reconstructed the climate history of Southeast Africa to identify possible reasons for the extinction of this species. The results are now published in Nature.

Climatic change causes environmental change that organisms must adapt to over the generations. If populations do not manage to adapt, their individuals die and occasionally a whole species becomes extinct. Based on a sediment core that was retrieved off the coast of Southeast Africa the team tracked down past changes. Here, the river Limpopo flows into the Indian Ocean. It transports sediment including microfossils like pollen from the land into the ocean that deposits on the sea floor. Like this, the composition of the sediment serves as a witness of the climate and environments of the past.

Amongst other things the team investigated hydrogen and carbon isotopes of plant waxes as well as the occurrence of pollen. Together with data from previous studies the scientists were able to make statements on the climate history of East Africa over the past 2,14 million years, covering the time period during which Paranthropus robustus lived in and went extinct.

Accordingly, about one million years ago a trend towards dryer conditions initiated in eastern Africa that lasted until about 600 000 years ago. The scientists assume that this may have caused a contraction and fragmentation of humid and wooden habitats in favour of hominids. Like this, the whole population of Paranthropus robustus was probably split up and diminished what may have served as an important factor in the final extinction of the species. In conclusion, changes in climate were probably an important factor for the demise of Paranthropus robustus. (ak)

Original study: Caley, T., Extier, T., Collins, J.A., et al., 2018. A two-million-year-long hydroclimatic context for hominin evolution in southeastern Africa. Nature. DOI: 10.1038/s41586-018-0309-6

Press Release, MARUM - Center for Marine Envirunmental Sciences at the University of Bremen

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