As the human species epxanded across the globe, we had to compete with other animals going for the easy food. We went for things like the small hard grass seeds we call cereals, which are indigestible if eaten raw and may even be poisonous, which we have to pulp up and turn into things like bread and dough. And we went into the poisonous giant tubers, like the yam and the taro, which also had to be leeched, ground up and cooked before we could eat them.
Martin Jones, Professor of Archaeological Science, Cambridge University