On hermit crabs and humans.

Flynn, Laland, Kendal and Kendal’s article (this issue) plays a valuable role in two ways. First, it demonstrates how developmental psychology can learn lessons from the latest research on developmental niche construction within evolutionary biology. Secondly, for those psychologists whose main focus is the cognitive mechanisms by which humans develop their particular suite of abilities, it is a useful reminder of the vast contribution of culture to shaping the modern human mind. Indeed, it is interesting to speculate on how much of the explanation of the abilities of modern humans should be properly apportioned to mechanisms of cognitive development compared to the extended accumulation of years of accumulation of cultural knowledge, practices, and artefacts that provide the social and educational niches within which humans are raised. In this commentary, however, I want to focus on the evolution. How much of the evolutionary dimension of niche construction theory (NCT) should we import into developmental psychology? Evolutionary psychology already exists as a sub-field of psychology. Developmental psychologists have sometimes viewed this sub-field with suspicion, particularly with respect to high-level cognition – not because there is any doubt that evolution has shaped us, but because evolutionary theories of high-level behaviour can sometimes appear as ‘just-so’ or post-hoc explanations, based on tenuous inferences about the selective pressures operating during the emergence of Homo sapiens. Moreover, evolutionary theories of high-level cognition are rarely constrained by neurobiological theories about the bespoke processing mechanisms that genes could feasibly deliver during brain development. Nevertheless, Flynn et al.'s article is timely. Recent work within the evo-devo framework (e.g. Finlay, 2007) has begun to address the interface between evolution and brain development. And the relative importance of – and correlation between – genes and environments is increasingly recognised within behavioural genetics (e.g. Plomin, DeFries, McClearn & McGuffin, 2008). Gene–environment correlations are typically separated into three types: passive correlations (environments that are inherited along with genes; e.g. children who inherit genes for attention deficit hyperactivity disorder are more likely to be raised in an environment shaped by impulsive parents); evocative correlations (environments that are evoked by the inherited traits of the individual; e.g. pretty children may evoke different responses from carers than less pretty children), or active correlations (by virtue of their inherited traits, an individual seeks out or creates certain environments; e.g. an introvert might apply for a job working in a library). Niche construction falls most comfortably under the umbrella of active gene–environment correlation. With respect to niche construction, the key question is, if humans are held to be the ultimate niche constructors (Smith, 2007), to what extent is the explanation for this an evolutionary one? Consider two different positions. On the one hand, perhaps humans are similar to hermit crabs. Hermit crabs depend on gastropod shells for protection. They construct a much safer niche than their own body provides. Living in shells has constrained the evolution of hermit crab bodies by requiring a soft asymmetrical abdomen that can be coiled into a gastropod shell. Here, evolution of the organism has occurred in the context of its niche construction abilities. If humans are similar, there will be particular aspects of our niche constructing abilities that are directly explainable in evolutionary terms. We just need to find the mental faculties that correspond to the hermit crab’s soft, asymmetrical abdomen. But note, for this adaptive process to take place across evolution, the niche construction has to correlate with the genome. That is, a niche constructing proto-ability, which confers some