This term I’ve started teaching a new module ‘Cognitive Evolution’ with my colleague Dr Sam Smith. We’re only two weeks into the start of the term but already it’s throwing up some really interesting questions about why Homo sapiens have such large brains. Not just a little bit big, but really really big! If you compare the primates to all other mammals then they emerge as being ‘brainier’ but then when you look inside the primate order it’s the genus Homo that really start to look like an outlying group. When you look within the genus there are roughly four species that start to follow the pattern of having big brains and display ‘advanced’ behaviours (namely Homo ergaster, Homo heidelbergensis, Homo neanderthalensis and Homo sapiens). It can be so easy to see this as an inevitable pattern of bigger = better. Brains get bigger and technology becomes better etc. But the archaeology does not directly correlate with the fossil data – for instance Homo ergaster continued to use Mode 1 tools for about 400,000 years before developing Mode 2 Tools despite having a brain almost twice as large as Australopithecus (Homo) habilis the ‘first; stone tool maker.
Selective pressures are really hard to identify in the fossil record and it notoriously easy to create a misleading narrative (we humans do love a pattern) when looking at human evolutionary themes. In other words just because we have big brains and use them to do lots of whizzy things today that’s not the same thing as understanding why they evolved. That’s whats so frustrating – the reason our brains are so large is one of the key questions facing palaeoanthropologists but why they did evolve is so hard to fathom. The selective pressures must have been immense to have evolved such a large and energy consuming organ. Big brains need energy, ours consumes roughly 22% of our daily calorific needs – for natural selection to have produced this state the evolutionary need must have been huge since regular access to high calorie food resources would have been vital for survival. As ever with human evolution there are a number of competing theories – some argue that our brains have evolved to allow for ever increasing social complexity, while others point towards the relationship between brain size and technological complexity. I lean towards manipulation as one of the key drivers of selection for bigger and bigger brains in Homo. This ‘lying, cheating and stealing’ model might not be the most uplifting of thoughts but certainly fits with our behaviour as a species.
thescienceofhumanevolution 