Built for speed: Pleistocene climate variation and the origin of human culture

Abstract

Recently, several authors have argued that the Pleistocene climatic fluctuations are responsible for the evolution of human anatomy and cognition. This hypothesis contrasts with the common idea that human language, tools, and culture represent a revolutionary breakthrough rather than a conventional adaptation to a particular ecological niche. Neither hypothesis is satisfactory. The “Pleistocene hypothesis”, as proposed, does not explain how Pleistocene fluctuations favor the particular adaptations that characterize humans. The alternative hypothesis does not explain what has prevented many animal lineages in the remote past from evolving a similar adaptive complex of tools, language and culture. Theoretical models of the cultural evolutionary process suggest some answers to these questions. Learning, including social learning, is rather generally a useful adaptation in variable environments. The progressive brain enlargement in many mammalian lineages during the last few million years suggests that climatic deterioration has had the general effect predicted by the Pleistocene hypothesis. Increased dependence on simple social learning was a preadaptation to the evolution of a capacity for complex traditions. The evolution of a costly capacity to acquire complex traditions is inhibited because, initially, complex traditions will be rare. Having the capacity to learn things that are far too complex to invent for oneself is not useful until traditions are common, but traditions cannot become complex before the capacity to acquire them is common. This problem may explain why many animals became more sophisticated learners in the Pleistocene, but why complex, cumulative cultural traditions are so rare. The history of our lineage must have included unique preadaptations that permitted us to evade the useless-when-rare problem.

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