There are lots of theories about what caused human evolution. Here’s a new one: cooking!
When humans invented cooking, it increased the number of calories they consumed, since heat breaks down cellulose in plants, making them more digestible and releasing the nutrients. Before the discovery of fire, we would have had to forage for 9 hours a day in order to get the same number of calories.
This could be the reason that other primates, such as gorillas, may have bodies 3 times larger than ours, but still have much smaller brains, despite the fact that they spent almost 8 hours a day foraging for food.