The source for the graph is Robin Dunbar, “Neocortex Size as a Constraint on Group Size in Primates”, Journal of Human Evolution, 20, 1992, pp 469–493. The correlation between the mean group where N is the mean group size and CR is the neocortex ratio (the ratio of neocortical volume to the volume of the rest of the brain). The value of 147.9 indicated by the regression for humans is an extrapolation from the results for the other primates. The use of both major axis and least-squares regression, as well as alternative indices of relative neocortical size, all yield equations that are of about this magnitude. With a neocortical volume of 1006.5 cc and a total brain volume of 1251.8 cc, the neocortex ratio for humans is 4:1. If the same correlation between the neocortex ratio and mean group size holds for humans as for the other primates, the mean group size for humans is 147.9. This correlation, not drawn by Dunbar, has been added in the graph. Log10(N) = 0.093 + 3.389 log10(CR) (r2 = 0.764, t34 = 10.35, p

David Fleming
Dr David Fleming (2 January 1940 – 29 November 2010) was a cultural historian and economist, based in London, England. He was among the first to reveal the possibility of peak oil's approach and invented the influential TEQs scheme, designed to address this and climate change. He was also a pioneer of post-growth economics, and a significant figure in the development of the UK Green Party, the Transition Towns movement and the New Economics Foundation, as well as a Chairman of the Soil Association. His wide-ranging independent analysis culminated in two critically acclaimed books, 'Lean Logic' and 'Surviving the Future', published posthumously in 2016. These in turn inspired the 2020 launches of both BAFTA-winning director Peter Armstrong's feature film about Fleming's perspective and legacy - 'The Sequel: What Will Follow Our Troubled Civilisation?' - and Sterling College's unique 'Surviving the Future: Conversations for Our Time' online courses. For more information on all of the above, including Lean Logic, click the little globe below!

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