Smell Ya Later?

Walk around an airport and you may find police officers with dogs, sniffing people and their belongings in search of drugs or other contraband. The dogs are there because they’re much better at detecting trace amounts of smells than we are, and it isn’t even close. As a species, we really don’t do a great job in picking up different odors. Why not?

Maybe it’s not that important. Evolutionarily speaking, that is.

Evolution, if we oversimplify it, goes like this: Organisms have certain genetically-determined traits, but every once in awhile a randomly-occurring genetic mutation pops into the mix. If that mutation makes the organism less likely to survive or reproduce, the mutation similarly is not passed down to the (non-existent) next generation. But if the mutation has a positive effect on the survival and/or reproduction of the organism, the difference carries on to the next generation. Fast forward by an unfathomably long amount of time and small mutations redouble and accumulate, and the evolution of species becomes noticeable.

But sometimes, mutation happen which make us weaker — but don’t make us necessarily less likely to survive or have babies. As it turns out, our sense of smell likely sits in that category.

Here’s the theory: As we evolved from four-legged animals to two-legged ones, some of our other senses became increasingly important. Having hands makes a tactile feedback important, for example. Being upright means that better vision is disproportionately advantageous, as the higher vantage point means a larger viewable area — assuming your eyes are up to the task, that is. Similarly, but on the other hand, being further away from the ground means that our sense of smell — in theory, at least — should become less important. We’re not likely to rely as much on information that, from an evolutionary perspective, we’ve been moving away from.

As a result? We’re losing the ability to detect some smells. Nat Geo explains:

We can distinguish between a vast number of different odors, thanks in part to the vast number of olfactory receptor genes our neurons can choose from. So far scientists have identified 390 different genes in the human genome that encode olfactory receptors.

But they’ve also found something else that’s rather stunning. The human genome contains another 468 olfactory receptor genes that neurons cannot use to make a receptor. They’re known as pseudogenes (“false” genes). While their sequence is overwhelmingly similar to working olfactory receptor genes, these pseudogenes carry mutations that make it impossible for a neuron to translate their sequence into a protein.

Take, for example, the smell receptor called OR7D4. It’s good at detecting androstenone, a smell which comes from pigs and, specifically, boar meat. And the smell is typically not a good smell — it’s called “boar taint,” and most people who can detect it find it so offensive as to make the otherwise safe meat inedible. But not everyone can smell it.

Per a release, in 2015, a team of researchers from lead by Dr. Kara Hoover, a researcher at the University of Alaska, “studied the DNA that codes for OR7D4 from over 2,200 people from 43 populations around the world, many of them from indigenous groups.” Our ancestors had the smell receptors, as do many of the tested groups who live in Africa. But “those from the northern hemisphere tend not to,” per the study. And maybe — and this is speculation — that’s because their ancestors’ exposure to boar meat was from domesticated boars. Those boars are safer to eat, the theory goes, so forgoing those calories would be a mistake, all else equal.

Either way, though, one thing is clear — our sense of smell is getting worse. But that doesn’t seem to be anything to be concerned about.


Bonus fact: A non-evolutionary benefit of humans having an increasingly weak sense of smell? The unique flavors of Ben & Jerry’s ice cream. Ben Cohen — the “Ben” of “Ben & Jerry’s” — has a condition called anosmia (“the inability to perceive odor” per Wikipedia) and favors food with more texture than smells. As a result, Ben & Jerry’s ice cream has a lot of large chunks of curious additions in most of its products.

From the Archives: The Nose Knows: How Disney’s theme parks use our (still-existing) sense of smell to market to us.

Related: A combination lock to keep your Ben & Jerry’s safe from prying spoons of others.