Why do dogs have a better sense of smell than we do?

Dogs have a better sense of smell than we do because the physical structure of a dog is better adapted for scenting odours. In dogs this sense has remained keen, while in man it has become comparatively dull. Dogs use scent in feeding, detecting enemies, recognizing mates and offspring and in rivalry.

The chemical sense of smell is called chemoreception and the sense organs chemoreceptors. But there is little in the structure of the nose to provide clues about its mechanism, and relatively little is known about how smell works. There are no accessory structures in the nose, and the receptors and nerve fibres leading to the brain are so fine that they are difficult to study. The chemoreceptors of human beings, dogs and other mammals lie in a cleft in each nostril.

During quiet breathing the main flow of air by-passes the cleft. But when a mammal sniffs, air is drawn into the clefts and over about half a square inch of yellowish tissue in which are embedded several million chemoreceptors. They are long thin cells with hair-like crowns making a web lying on the surface of the tissue which is bathed in mucus. These are connected to a part of the brain called the olfactory bulb, the size of which is a fair indication of the keenness of the sense of smell.

The olfactory bulb of a dog is much larger than that of a man. The moist nose of a dog also aids his sense of smell.

Smells are immensely important to dogs as we see from the way they refuse to by-pass a scent without investigating it and, very often, adding to it. They mark their home range and investigate passer-by. Their keen sense has been used by man as a help in hunting and tracking for many thousands of years.