It smells like a breakthrough, but it's always been right there in front of them. Scientists at Stanford University in California say they have discovered why humans have two nostrils.

The researchers, including Canadian post-doctoral student Rehan Kahn, have suggested that each nostril transmits slightly different information to the brain. Like each eye and each ear, each nostril takes in and relays complementary information.

Their experiments show that each nostril has better detection of certain smells. So, while the left nostril might detect burning smells better, the right detects flowery scents more easily.

The scientists say that a difference in airflow through the nostrils allows one nostril to better detect the odor of some substances while the other better detects others. The researchers also say that this smell specialization moves back and forth between the nostrils.

The study is in the November 4 issue of the journal Nature.