Over the last 20,000 years, human brains have shrunk 10%: that’s a chunk the size of a tennis ball – scary stuff – and that’s before you even consider variations based on age, sex, class and race. Why? Well there are a good few theories. Some say it’s linked to the body size decline that was favoured by the warming trend in the earth’s climate; others believe the advent of agriculture left us chronically malnourished. A different option all together is Geary’s “Idiocracy Theory” that domestication and cultural support has allowed us to live with lower IQs; although others link this domestication to the breeding out of aggressive tendencies, which usually comes with a whole host of genetic consequences. Recently, Hood’s entered the debate with his new book, The Domesticated Brain. This is, however, a tricky field, and an equally compelling argument is that put forward by Hawks – we’re actually getting smarter, and our brains are far more efficient now. Everything gets even more complicated, when you look at the bigger picture, as our brain size has actually tripled in the last 2 million years – something also linked to social competition.