Hominin population connectivity and isolation across the Mid-Pleistocene Transition: Toward an application of density-based spatial clustering in understanding mechanisms of hominin macroevolution Open Access
Lin, Theodore (Spring 2026)
Abstract
Understanding the processes of speciation, extinction, and diversification has been a key and enduring objective in paleoanthropology. Interest in the role of ecological and climatic factors in these macroevolutionary processes likewise has a history extending back to Darwin, Wallace, and contemporaries, and continuing through Mayr, Vrba, and the Modern Synthesis. However, comparatively little effort has been dedicated to understanding the biogeographical mechanisms underpinning these processes in hominins. Exactly how, and to what exact degree, changes in climate and habitat have mechanistically influenced population-level processes in the course of hominin evolution remain important, yet understudied, questions.
The Mid-Pleistocene Transition (“MPT,” ~1.2–0.8 Ma) marks the onset of the prolonged and extreme glacial cycles characteristic of the later Pleistocene: a fundamental shift in the paleoecological context of hominins, and of Earth’s biota as a whole. The glaciations and deglaciations of the post-Transition Pleistocene have been previously demonstrated to be significant determinants of the extent of hominin habitats, which may have produced alternating periods of high population connectivity followed by extended isolation. Here, I apply density-based spatial clustering algorithms to existing hominin occurrence data in order to (1) quantitatively identify populations of hominins, and (2) compare patterns of population connectivity and isolation pre- and post-MPT, from a fossil-biogeographic approach. More specifically, we ask whether differences exist between these periods in the size and number of hominin occurrence clusters, in the geographical and ecological distance between them, and in the persistence or replacement of populations therein. Changes in patterns of vicariance, ecological diversification, and turnover, as seen through these proxies, may provide novel insights into the mechanisms behind the taxonomic “muddle” of the Mid- to Late Pleistocene.
Table of Contents
Table of Contents
Background & Introduction................................................................................................... 1
The Mid-Pleistocene Transition................................................................................. 1
Hominin Evolution during the Middle Pleistocene................................................... 2
The Metapopulation and Speciation.......................................................................... 6
Cluster Analysis and Biogeography........................................................................... 9
Materials & Methods............................................................................................................. 13
Extant Taxa as Models............................................................................................... 13
Density-based clustering of extant taxa......................................................... 13
Simulation of taphonomic processes using random removals....................... 14
Density-Based Clustering of Fossil Hominins........................................................... 15
Results.................................................................................................................................... 20
Extant Taxa................................................................................................................ 20
Complete datasets.......................................................................................... 20
Random removals.......................................................................................... 23
Fossil Taxa................................................................................................................. 28
Homo neanderthalensis................................................................................. 28
Homo heidelbergensis ................................................................................... 31
Homo erectus (s.l.)......................................................................................... 34
Discussion.............................................................................................................................. 40
Density-Based Clustering and Hominin Biogeography............................................. 40
Homo neanderthalensis................................................................................. 40
Homo heidelbergensis ................................................................................... 43
Homo erectus (s.l.)......................................................................................... 45
Limitations and Future Directions............................................................................. 47
Bibliography.......................................................................................................................... 54
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