The Role of Character Displacement and Ecological Niche Incumbency in Hominin Evolution
Open Access DepositedBroader biogeographical principles have largely been ignored in discussions of eastern African Paranthropus paleoecology. Most of these discussions have not moved beyond the premise that because Paranthropus disappears from the fossil record by c.1 Ma, then its competitive inferiority relative to early Homo led to its demise. However, alternative models of competition (i.e. ecological niche incumbency versus character displacement) have never been tested between these two hominin genera. In this dissertation, I discuss how the current fossil and paleoecological evidence for Paranthropus and Homo is consistent with alternative scenarios in which a non-ancestral lineage can significantly impact the evolution of a surviving lineage. I then verify that early Homo and Paranthropus were not merely in the same place at the same time, but were actively interacting with each other (i.e., ‘functional sympatry’). This is tested quantitatively through Hutchinson’s rule, where the ratio between mastication-related linear measurements can signal whether sympatric species have adequately niche-partitioned along their dietary axes. Lastly, I use 3D geometric morphometrics on over 130 Paranthropus and early Homo fossils scanned at the National Museums of Kenya to differentiate between ecological niche incumbency and character displacement, two potential manifestations of competition that could have occurred between eastern African hominins during the Pleistocene. This dissertation provides a shift in our theoretical frameworks as they apply to competition between hominins in eastern Africa and shows how a non-ancestral, non-surviving lineage can significantly impact the evolutionary lineage of our own genus: Homo.
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