Climate Change Predictive of Body Size and Proportionality in Humans

Abstract The effects of climate change on plants and animals have been examined across numerous species, yet little evidence has been produced to demonstrate an influence on human evolution. Here the impact of climate change on human body size and scaling is examined over a period of 700,000 years using five independent paleoclimate records. Across 247 Homo specimens, body mass averaged significantly smaller during periods of climatic warming as compared to cooler cycles. Body proportions also changed significantly, appearing more ectomorphic during warmer periods and more endomorphic during periods of cooling across a sample of 87 specimens. The results indicate a relationship between climate change and body size and shape in humans that is driven by natural selection in response to thermoregulatory demands. The findings suggest that body size adaptations in response to climate change occurred early and potentially implicated cultural adaptations in later periods, muting the morphological response to extreme climates. Because morphological variation has been used as a factor for classification within the genus Homo , taxonomic and phylogenic decisions may need to be reconsidered in the context of temporal climate differences.