Men have larger noses than women because they have more muscle, demanding bigger noses to breathe in more oxygen, a new study has found.
The study from the University of Iowa found that men's noses are about 10 per cent larger than female noses, on average, in populations of European descent.
The size difference, the researchers believe, comes from the sexes' different builds and energy demands: Males in general have more lean muscle mass, which requires more oxygen for muscle tissue growth and maintenance.
Larger noses mean more oxygen can be breathed in and transported in the blood to supply the muscle.
The researchers also noted that males and females begin to show differences in nose size at around age 11, generally, when puberty starts.
Physiologically speaking, males begin to grow more lean muscle mass from that time, while females grow more fat mass.
"This relationship has been discussed in the literature, but this is the first study to examine how the size of the nose relates to body size in males and females in a longitudinal study," said Nathan Holton, assistant professor in the UI College of Dentistry and lead author of the paper, published in the American Journal of Physical Anthropology.
"We have shown that as body size increases in males and females during growth, males exhibit a disproportionate increase in nasal size.
"This follows the same pattern as energetic variables such as oxygenate consumption, basal metabolic rate and daily energy requirements during growth," Holton added.
It also explains why our noses are smaller than those of our ancestors, such as the Neanderthals. Our distant lineages had more muscle mass, and so needed larger noses to maintain that muscle, researchers said.
"So, in humans, the nose can become small, because our bodies have smaller oxygen requirements than we see in archaic humans," Holton said, noting that the rib cages and lungs are smaller in modern humans, reinforcing the idea that we don't need as much oxygen to feed our frames as our ancestors.
For the study, Holton and his team tracked nose size and growth of 38 individuals of European descent enrolled in the Iowa Facial Growth Study from three years of age until the mid-twenties, taking external and internal measurements at regular intervals for each individual.
They found that boys and girls have the same nose size, generally speaking, from birth until puberty percolated, around age 11. From that point onward, the size difference grew more pronounced.
