When listing animals with a keen sense of smell, people are not likely to place their own species, humans, at the top, perhaps picking rabbits or dogs instead. But in this Review, John McGann points to evidence, from a variety of research efforts, that the belief that humans have an inferior sense of smell may be more a remnant of an old myth than a hypothesis based on fact. He notes that the origin of this belief dates back to the 19th century, when prominent neuroanatomist and anthropologist Paul Broca discovered that the relative size of a brain region across various species correlated with these species' abilities, respectively, to perform tasks associated with that brain region; because humans have a relatively smaller olfactory bulb, the region of the brain responsible for processing smell, he assumed that humans' ability to smell is inferior to that of other animals. However, McGann points to more recent evidence suggesting that the olfactory bulb may be an exception to the rule that brain region size equates to associated ability. Intriguingly, he also notes that the number of neurons in the olfactory bulb is fairly consistent across species; for example, a study found that, across a diverse group of mammals, a 28-fold range in the number of olfactory bulb neurons persists despite a 5800-fold range in body weight. After discussing the role of several other biological factors that may contribute to smell sensitivity, such as genes and neurogenesis, McGann highlights experimental work suggesting that each species may simply be more sensitive to different scents; for example, humans were found to be more sensitive than dogs to a compound found in bananas. McGann highlights a number of ways in which smell is important to humans, such as for communication and mate choice, concluding that humans' sense of smell is likely much more important than previously believed.