Smell: an ancient animal sense

DETECTING CHEMICALS IN THE environment enables an individual to identify molecules secreted by predators or prey, potential poisons and sexual partners. This benefit D to survival and reproduction helps explain why smell - olfaction - is probably the oldest sense and evolved 500 million years ago, around the origin of animals.

- JV CHAMARY

What's the difference between taste and smell?

The distinction is down to whether a chemical is already dissolved in water or if it is airborne. Your tongue's tastebuds identify five flavours (bitter, salty, sweet, sour and savoury/umami) in liquids, while your nose's sensors can detect numerous odour molecules odourants that are airborne before they dissolve in the moist lining of your nasal cavity. But that's for terrestrial species. For aquatic creatures such as fish, all molecules are in water so there's no real distinction between gustation (taste) and olfaction (smell).

How does olfaction work?