Mammals’ sense of smell is the oldest of the five senses and evolved in response to the environment. This sense is crucial to survival, protecting mammals against natural predators and helping them to avoid things that have gone rotten. For humans, olfaction also enables us to enjoy what we eat. It has been posited that humans’ sense of smell exhibits a synergistic effect, in which the brain develops in order to obtain better food, with the pursuit of tastier food then resulting in the brain growing in size. Having evolved in this specific way in humans, olfaction might hold the key to unlocking the mystery of human evolution.