Abstract
To understand human evolution it is critical to clarify which adaptations enabled our colonisation of novel ecological niches. For any species climate is a fundamental source of environmental stress during range expansion. Mammalian climatic adaptations include changes in size and shape reflected in skeletal dimensions and humans fit general primate ecogeographic patterns. It remains unclear however, whether there are also comparable amounts of adaptation in humans, which has implications for understanding the relative importance of biological/behavioural mechanisms in human evolution. We compare cranial variation between prehistoric human populations from throughout Japan and ecologically comparable groups of macaques. We compare amounts of intraspecific variation and covariation between cranial shape and ecological variables. Given equal rates and sufficient time for adaptation for both groups, human conservation of non-human primate adaptation should result in comparable variation and patterns of covariation in both species. In fact, we find similar amounts of intraspecific variation in both species, but no covariation between shape and climate in humans, contrasting with strong covariation in macaques. The lack of covariation in humans may suggest a disconnect in climatic adaptation strategies from other primates. We suggest this is due to the importance of human behavioural adaptations, which act as a buffer from climatic stress and were likely key to our evolutionary success.
Highlights
Understanding the nature of the adaptations that enabled Homo sapiens to become such a successful species, colonising the vast majority of ecological niches globally, is a key question in the study of human evolution
In a recent paper[12], we showed that Japanese macaques from different latitudes throughout the Japanese Archipelago show craniofacial and postcranial differences in morphology which correspond with neither dietary differences nor phylogenetic patterns
Does comparable climatic stress lead to comparable cranial adaptation in humans and in non-human primates, or do similarities between northern Japanese macaques and humans from much higher latitudes imply that more severe cold stress is required to impact the human phenotype? To address this question, we compare differences in craniofacial morphology between groups of Japanese macaques from sites throughout Japan with ecologically comparable groups of Japanese prehistoric foragers (Jomon)
Summary
Understanding the nature of the adaptations that enabled Homo sapiens to become such a successful species, colonising the vast majority of ecological niches globally, is a key question in the study of human evolution. Www.nature.com/scientificreports macaques resembles the characteristic differences between very high latitude people and those from lower latitudes[16,18,19] This suggests that humans do not diverge from a non-human primate pattern of adaptation in this respect. Compared to the cranial data, there is a greater degree of consensus that Jomon postcrania conform to ecological expectations of size, obeying Bergmann’s rule, limb proportions do not seem to obey Allen’s rule[32,34,35] This potential difference in responsiveness to climate between the cranium and postcrania may reflect differences in plasticity and canalisation inherent to the different skeletal regions[36,37]. GMM preserve the geometry of shapes under analysis and allow the modelling of shape differences within a sample that are associated with other types of variable, such as ecological data
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