Olfaction is one of the least understood senses but has played a vital role in the evolution of vertebrates. Basic survival behaviors such as foraging, communicating, recalling memory, and reproduction are often dependent on a protruding-facial structure that we too often ignore.
In a similar fashion to the eye’s ability to recognize the wavelength of light, sensory receptors embedded in a patch of tissue in the nasal cavity of the nose respond to airborne chemicals. Scientists do not yet understand the exact mechanism, but evidence suggests that the shape and fit of the receptor and chemical determine how the brain registers the odor.
For humans too, odors that activate the “forgotten sense” are intimately linked with our emotion centers, associating themselves with intense feelings and memories. Noisome smells, such as the waft of a rotten egg, and fragrant ones, such as your favorite air freshener, catalyze the release of neurotransmitters that drive an appropriate action. Retreat or approach? Your nose knows what to do, often before you do.
But it may also determine who you develop feelings for, as sweat from the human body has been shown to reveal underlying clues about the strength of a potential mate’s immune system. The sweeter the smell, the more varied the immune system.
The importance of olfaction is perhaps more salient in the natural world, among our evolutionary cousins.
Though common birds have relatively small olfactory bulbs, others rely on an extraordinary sense of smell to find food: Turkey Vultures can detect the gas of rotting flesh from miles above in the sky; Wilson’s Petrels recognize the odor of plankton, indicating that fish is nearby; Pileated Woodpeckers rely on a trail of formic acid to locate delicious ants; New Zealand’s Kiwi sniff out insects in leaf litter; and honeyguides effortlessly locate concealed beeswax candles. Sniff then eat, sniff then eat.
However, for birds, like many other animals, smell is a multi-functional sense.
Researchers from the University of Chicago and the Chicago Zoological Society Penguins published findings this week showing that smell acts a primary mechanism for kin recognition among Humboldt Penguins. When prompted to spend time and choose among a suite of enclosures lined with different oils, penguins spent more time near the familiar odor. The ability to recognize kin may help penguins identify more suitable mates, reducing the risk of inbreeding.
Scientists once believed that the sense of smell declined as birds developed heightened senses of vision, hearing and balance for flight. But when comparing the olfactory bulbs in the brains of many species of dinosaurs and modern birds, researchers found that odor detection capabilities actually increased.
Mammals too seem to have evolved bigger and more specialized brains to process smells that originally aided in hunting at night. When researchers compared the shape of their brain cases to those of pre-mammals, areas associated with the sense of smell were observed to be the first to overdevelop.
After years of evolutionary tinkering, the vertebrate nose has become the ultimate tool of survival. Your nose knows it, and now you do too.