Department of Archaeology, University of Cambridge
April 17, 2020 21, Platinum Ballroom
The hominin lineage is exceptionally speciose. What remains unknown is whether the increased diversification this speciosity hints at also occurred below the species level, as Darwin predicted in his “Manufactory Hypothesis”. That is, should we expect hominin species to have comprised more subspecies than other apes? And what evolutionary “role” might subspecies have played in the generation of hominin diversity?
We first establish the general trends in the relationship between subspecies richness and species richness in all mammals. Species range is the most significant predictor of subspecies richness in all clades (p<0.001). Ecological substrate, further, mediates the strength of the correlation between generic speciosity and average subspecies per species: it is stronger in non-terrestrial mammals (Kendall’s tau=0.27, p<0.001 in non-terrestrial groups and 0.11, p<0.001 in terrestrial groups). Primates are an exception to this, with a tau of 0.24. We then simulate three models of diversification to predict, based on known species richness, how many subspecies per species a clade should comprise.
We then tested whether subspecies richness correlates with intrinsic traits (age at female maturity, body mass, and dietary diversity) regardless of extrinsic context in 386 species from four mammalian higher taxa (Primates, Carnivora, and Cetartiodactyla). In Primates, slower life histories are associated with higher subspecies richness.
Based on these results, we predict likely numbers of subspecies key hominin taxa will have comprised. We conclude by discussing whether or not hominin subspecies can be considered incipient species, and how we might detect them in the fossil record.
This work is funded by a St. John's College Benefactor's Scholarship and Cambridge University Vice-Chancellor's Scholarship.