The 82nd Annual Meeting of the American Association of Physical Anthropologists (2013)

Reconstructing phylogenetic relationships and evolutionary processes in early Homo evolution: genetic drift or selection?


Department of Archaeology, University of Cape Town

Friday 9:30-9:45, Ballroom B Add to calendar

The discovery of the somewhat Homo-like Au. sediba has fuelled a growing number of debates surrounding the phylogenetic relationships in the Homo lineage. These discussions are complicated by our partial understanding of the underlying evolutionary processes acting to produce the diverse morphology characterizing this time period, fundamental in determining and understanding different potential evolutionary scenarios.

Here we apply statistical tests developed from quantitative evolutionary theory to estimate the causal factors (genetic drift vs. selection) behind morphological divergence during the early evolution of our genus. Analyses are performed on 3-D scan data collected from cranial and mandibular specimens of early Homo from eastern and southern Africa, Au. sediba and Au. africanus. If drift is rejected, selection vectors are then reconstructed to understand the magnitude and direction of selection.

Results from all analyses reject drift when investigating morphological divergence between southern and eastern early Homo, Au. sediba and Au. africanus. Estimated selection vectors and morphological responses for each analysis show that the selection required to produce east and South African early Homo from Au. sediba is straightforward in direction and magnitude, whereas Au. africanus to early Homo is more complex. However, genetic drift may explain the divergence between the earliest Homo specimens and later early Homo. Overall, these results suggest that the selection needed to change from Au. sediba to Homo is a more likely adaptive scenario than one including Au. africanus. However, a transition from the earliest Homo specimens (Hadar, Uraha) to later Homo is arguably a simpler evolutionary pathway.

This study was funded by the L.S.B. Leakey Foundation (Franklin Mosher Baldwin Fellowship), Palaeontological Scientific Trust (PAST), and South African National Research Foundation (NRF).

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