Growing Pains: Opportunities to Adjust Phenotypic Trajectories in Childhood and Adolescence Complicate Studies of Developmental Plasticity in Late Homo

Developmental plasticity, the ability to regulate aspects of development in response to environmental cues, is hypothesized to evolve in response to environmental heterogeneity and may facilitate dispersal, novel habitat occupation, and niche construction. Although the adaptive value of developmental plasticity is a topic of debate in biological anthropology, alternative phenotypes associated with developmental stress observed in living human populations may have been fitness enhancing in the novel and marginal environments encountered by our ancestors. For these reasons, there has been increased interest in studying developmental plasticity in skeletal biology, with the goal of assessing how plastic developmental processes have contributed to the patterning of phenotypic variation, disease susceptibility, and mortality risk in both modern humans and fossil hominin populations. What we currently know about hominin evolution suggests that, after the emergence of Homo erectus, climate change and repeated episodes of dispersal may have promoted the accumulation and maintenance of plastic traits in hominin populations. At the same time, our lineage developed life history traits thought to significantly increase risks associated with predictive plasticity (e.g., extended development, longer lifespans), alongside novel life history stages (e.g., childhood, adolescence) that created additional opportunities for environmental signals to inform development. It is therefore essential that we consider how derived features of hominin life history patterns shape opportunities for phenotypic-environmental interactions at the level of systems and tissues. In studies of developmental plasticity involving skeletal and fossil samples, this approach will facilitate more robust analyses of the relationship between environmental signals and corresponding phenotypic effects, and the identification of potential sources of bias related to “swamping”, compensatory plasticity, and equifinality.