Nice article from Dan Jones, mainly about how Robin Dunbar and various colleagues are investigating the affects on primate group size of climate and thus food availability, to get an ecological handle on human evolution. Raises interesting questions: as you move from chimps to Australopithecenes, brain/cranium size increases, suggesting larger social groups. But how did Australopiths eke out a sufficient existence to support larger groups and bigger brains? Did they roam more, temporarily fission into small groups, or (very unlikely) eat meat?
The article also goes on to look at how sexual dimorphism reduces from chimps to Homo erectus and man, suggesting a trajectory toward monogamy. How was female behaviour changing, and what had that to do with food availability? Jones also reports on work by Karen Isler and Carel van Schaik who plotted brain size against fecundity for over 1200 animal species. Normally, when brain size increases fecundity goes down, because of the inordinate investment in grey matter, but humans have the biggest brains of all animals and much higher fecundity than the great apes and earlier hominins. The answer? Allometernal care - helpers at the nest. It works for big-brained birds too. For primates, including us, they calculated the magic number for brain size at which reproductive effort will be compromised if step-mothers don't kick in - one litre!
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