Different environmental variables predict body and brain size evolution in Homo

Abstract

Increasing body and brain size constitutes a key macro-evolutionary pattern in the hominin lineage, yet the mechanisms behind these changes remain debated. Hypothesized drivers include environmental, demographic, social, dietary, and technological factors. Here we test the influence of environmental factors on the evolution of body and brain size in the genus Homo over the last one million years using a large fossil dataset combined with global paleoclimatic reconstructions and formalized hypotheses tested in a quantitative statistical framework. We identify temperature as a major predictor of body size variation within Homo, in accordance with Bergmann’s rule. In contrast, net primary productivity of environments and long-term variability in precipitation correlate with brain size but explain low amounts of the observed variation. These associations are likely due to an indirect environmental influence on cognitive abilities and extinction probabilities. Most environmental factors that we test do not correspond with body and brain size evolution, pointing towards complex scenarios which underlie the evolution of key biological characteristics in later Homo.

A spatiotemporally explicit paleoenvironmental framework for the Middle Stone Age of eastern Africa

“…Our application of high-resolution paleoenvironmental reconstructions has enabled a previously impossible characterisation of the ecosystems inhabited by early human populations at this scale, with existing site-based paleoenvironmental reconstructions being very useful but difficult to integrate and translate into a comprehensive framework for the region. Whilst the application of high-resolution climatic simulations to archaeological data is inherently limited by the uncertainty surrounding radiometric dates – indeed, future work should focus on developing methods that address the effects of dating error on conclusions derived from climatic models (see 51 ) – our results are important for demonstrating the environmental conditions inhabited throughout the eastern African MSA, with levels of diversity far beyond that typically assumed by classic habitat-specific hypotheses for human evolution 52 – 55 . By establishing the role of shifting environmental conditions and ecological boundaries on the distribution and variability of dated MSA assemblages, our work also helps illuminate some of the processes that shaped behavioural diversity during this key period, such as that MSA toolkits likely facilitated expansions into diverse environments, adding further complexity to within-region migration than environment tracking 56 .…”

Alternative Metabolic Strategies are Employed by Endurance Runners of Different Body Sizes; Implications for Human Evolution

“…Instead, the challenge was to be able to run well enough to enhance survival by scavenging and/or hunting to access nutrition. They did so using bodies of variable mass and proportions, shaped by environmental stress such as temperature, with larger body sizes typically found in colder, more open environments with greater frequencies of large game (Will et al, 2021). Individuals with good RE and lower body mass, common in warmer environments, could likely glide economically as they ran.…”

“…Considering climate, Bergmann's rule describes patterns of variation both within and across species relative to the temperature of their environment, with endotherms expected to be larger in colder environments (Bergmann, 1847). Recent research combining comprehensive palaeontological data with climate models demonstrates that temperature is the only environmental variable to correspond with variation in body size across the last one million years of hominin evolution (Will et al, 2021). While earlier Plio-Pleistocene increases in body size may have been driven by early hominin migrations into more variable environments and through changes in the hominin dietary niche (Will et al, 2017;, the recent analyses suggest that that thermal stress was the primary driver of variation in hominin body size within the genus Homo (Will et al, 2021).…”

“…Recent research combining comprehensive palaeontological data with climate models demonstrates that temperature is the only environmental variable to correspond with variation in body size across the last one million years of hominin evolution (Will et al, 2021). While earlier Plio-Pleistocene increases in body size may have been driven by early hominin migrations into more variable environments and through changes in the hominin dietary niche (Will et al, 2017;, the recent analyses suggest that that thermal stress was the primary driver of variation in hominin body size within the genus Homo (Will et al, 2021). Modern humans also show patterns of phenotypic variation consistent with Bergmann's rule Crognier 1981;Foster & Collard, 2013;Hiernaux, 1968;Hiernaux & Fromont, 1976;Holliday, 1997a, b;Holliday & Trinkaus, 1991;Ruff, 1994;Stinson, 1990;Tilkens et al, 2007;Trinkaus, 1981).…”

pastclim: an R package to easily access and use paleoclimatic reconstructions

“…e . ecology (Miller et al 2021a, b), paleoecology (Leonardi et al 2018, 2020, Somveille et al 2020, Chen et al 2021, Schap et al 2021, Thorup et al 2021), conservation (Beyer and Manica 2021), population genetics (Maisano Delser et al 2021), archaeology (Racimo et al 2020, Betti et al 2020, Beyer et al 2021, Krzyzanska et al 2021, Park and Marwick 2022, Cerasoni et al 2022, Timbrell et al 2022), the evolution of the genus Homo (Will et al 2021, Timmermann et al 2022), anthropology (Leonardi et al 2017, Padilla-Iglesias et al 2021) and linguistics (Beyer et al 2019).…”