Hominin cognitive evolution: identifying patterns and processes in the fossil and archaeological record

Abstract

As only limited insight into behaviour is available from the archaeological record, much of our understanding of historical changes in human cognition is restricted to identifying changes in brain size and architecture. Using both absolute and residual brain size estimates, we show that hominin brain evolution was likely to be the result of a mix of processes; punctuated changes at approximately 100 kya, 1 Mya and 1.8 Mya are supplemented by gradual within-lineage changes in Homo erectus and Homo sapiens sensu lato. While brain size increase in Homo in Africa is a gradual process, migration of hominins into Eurasia is associated with step changes at approximately 400 kya and approximately 100 kya. We then demonstrate that periods of rapid change in hominin brain size are not temporally associated with changes in environmental unpredictability or with long-term palaeoclimate trends. Thus, we argue that commonly used global sea level or Indian Ocean dust palaeoclimate records provide little evidence for either the variability selection or aridity hypotheses explaining changes in hominin brain size. Brain size change at approximately 100 kya is coincident with demographic change and the appearance of fully modern language. However, gaps remain in our understanding of the external pressures driving encephalization, which will only be filled by novel applications of the fossil, palaeoclimatic and archaeological records.

From side to side: Symmetry in handaxes in the British Lower and Middle Palaeolithic

“…This hominin evolutionary trajectory is often portrayed as a single upward cline, a slope of gradual development as for example in the iconic Social Brain graph (Dunbar et al, 2014;Gowlett et al, 2012), although a more punctuated interpretation is possible (McNabb and Cole, 2015;Shultz et al, 2012).…”

Are there alternative adaptive strategies to human pro-sociality? The role of collaborative morality in the emergence of personality variation and autistic traits

“…Selection for pro-social intentions and behaviours occurs from at least 1.5 million years ago, with increasing material evidence for care of the vulnerable (Hublin 2009;Spikins, Rutherford, and Needham 2010;Spikins 2015a) as well as displays of positive reputation in material culture (Spikins 2012). Complex social dynamics similar to those of modern hunter-gatherers and associated with collaborative morality become identifiable by at least 100,000 years ago (Spikins 2015b), which is commensurate with an expansion of the brain at this time (Shultz, Nelson, and Dunbar 2012). Widespread support for those who were physically vulnerable generated physically and cognitively diverse societies.…”

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“…The evolution of genus Homo from over 2 ma was marked by significant encephalization (de Miguel and Henneberg 2001;Shultz et al 2012). According to the social brain hypothesis (Byrne and Whiten 1988;Dunbar 1992Dunbar , 1998, this indicates they lived in progressively larger social networks.…”

“…here is a growing consensus that evolving Homo mothers relied on cooperative breeding to raise larger-bodied, larger-brained offspring (e.g., Aiello and Key 2002;Barrickman et al 2008;Burkart et al 2009;Robson and Wood 2008;Shultz et al 2012;van Schaik et al 2006 Models for cultural levels of human cooperation (Boyd and Richerson 1992, 2005Gintis et al 2003;Henrich and Boyd 2001;Henrich et al 2003Henrich et al , 2006Nowak and Sigmund 2005;Richerson et al 2003), invoke multilevel and group selection processes, but ignore what is most difficult to explain-how to secure cooperation between the sexes, given the trade-off between investing in current offspring versus future mating opportunities (cf. Bowles 2006).…”

“…here is a growing consensus that evolving Homo mothers relied on cooperative breeding to raise larger-bodied, larger-brained offspring (e.g., Aiello and Key 2002;Barrickman et al 2008;Burkart et al 2009;Robson and Wood 2008;Shultz et al 2012;van Schaik et al 2006). But many questions about pathways and mechanisms remain open.…”