The bewildering, complex picture presented by human evolution in the Middle to Late Pleistocene should be seen as a feature, not a bug, reflecting evolutionary processes in all their messy glory

Evolution of Homo in the Middle and Late Pleistocene. Katerina Harvati, HugoReyes-Centeno. Journal of Human Evolution, Volume 173, December 2022, 103279. https://doi.org/10.1016/j.jhevol.2022.103279

Abstract: The Middle and Late Pleistocene is arguably the most interesting period in human evolution. This broad period witnessed the evolution of our own lineage, as well as that of our sister taxon, the Neanderthals, and related Denisovans. It is exceptionally rich in both fossil and archaeological remains, and uniquely benefits from insights gained through molecular approaches, such as paleogenetics and paleoproteomics, that are currently not widely applicable in earlier contexts. This wealth of information paints a highly complex picture, often described as ‘the Muddle in the Middle,’ defying the common adage that ‘more evidence is needed’ to resolve it. Here we review competing phylogenetic scenarios and the historical and theoretical developments that shaped our approaches to the fossil record, as well as some of the many remaining open questions associated with this period. We propose that advancing our understanding of this critical time requires more than the addition of data and will necessitate a major shift in our conceptual and theoretical framework.

Keywords: Homo heidelbergensisNeanderthalsModern human originsSpeciationHybridization

5. Conclusions

While the issues presented and discussed here do not represent the full extent of questions related to human evolution in the Middle to Late Pleistocene, this brief review has shown that, although the human fossil record of Middle Pleistocene Homo is significantly more abundant than it was half a century ago and innovative methodologies have greatly expanded our ability to study it, the greatest gains in our understanding are likely to result from a theoretical and conceptual shift toward more complex and nuanced evolutionary concepts for both species and speciation. Additional challenges include a better understanding of the chronological and paleoenvironmental framework of the Middle to Late Pleistocene, as well as the lack of integrative, synthetic study of the fossil record in its entirety. We expect new fieldwork and fossil discoveries to continue to bring novel insights, and for genomic and paleoproteomic approaches to play a central role in deciphering the record, especially if they can be developed to be applicable in lower latitude and earlier contexts. Gene annotation methods that link genotypes and phenotypes and their modularity in diverse environmental contexts (Gokhman et al., 2017; Brand et al., 2022), as well as evolutionary modeling approaches, will be particularly useful in the absence of a more complete fossil record. However, the envisioned integrative approach will only be possible through broad sharing of fossil data, something which is still rare in paleoanthropology, even after the development and widespread use of scan data, which can be shared digitally much more efficiently among researchers, more than two decades ago (Weber, 2001; Gibbons, 2002; Tattersall and Schwartz, 2002).

In closing, we emphasize that the bewildering, complex picture presented by human evolution in the Middle to Late Pleistocene should be seen as a feature, not a bug, reflecting evolutionary processes in all their messy glory. We look forward to the next unexpected discovery!