Hypotheses: one out, one in

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November 20, 2020

The "Cradle of Humankind" Northwest of Johannesburg, South Africa comprises a number of limestone cave localities named Kromdraai, Sterkfontein and Swartkrans. (To this has been added another locality, named Rising Star.) A separate fossiliferous site, approximately 5 km from the famous fossil sites of Sterkfontein and Swartkrans, is Drimolen.  Drimolen and Sterkfontein come together in the November issue of the journal Nature Ecology & Evolution in an article entitled “Drimolen cranium DNH 155 documents microevolution in an early hominin species”.

The abstract of this paper states clearly what is to be demonstrated: Paranthropus robustus is a small-brained extinct hominin from South Africa characterized by derived, robust craniodental morphology. The most complete known skull of this species is DNH 7 from Drimolen Main Quarry, which differs from P. robustus specimens recovered elsewhere in ways attributed to sexual dimorphism. Here, we describe a new fossil specimen from Drimolen Main Quarry, dated from approximately 2.04–1.95?million years ago, that challenges this view. DNH 155 is a well-preserved adult male cranium that shares with DNH 7 a suite of primitive and derived features unlike those seen in adult P. robustus specimens from other chronologically younger deposits. This refutes existing hypotheses linking sexual dimorphism, ontogeny and social behaviour within this taxon, and clarifies hypotheses concerning hominin phylogeny. We document small-scale morphological changes in P. robustus associated with ecological change within a short time frame and restricted geography. This represents the most highly resolved evidence yet of microevolutionary change within an early hominin species.

Differences between DNH7 and other specimens of P. robustus have been attributed to sexual dimorphism. The findings described in this paper challenge this hypothesis. The authors of this paper reinforce their hypothesis rapid evolution took place between Drimolen,  dated between 2.04 and 1.95mya and the 200,000 year younger specimens of P. robustus found that Staerkfonteim.

Read theNature Ecology and Evolution paper.