How Did We Evolve a Sense of Smell?

Date: Cool, yeah.

So where are you from?

Tina: I'm from Genovia Waitress: Welcome to the Why Am I Like This restaurant.

Today's special is existential dread with a little bit of crying on the side.

We're just really excited to have you here.

Tina: Is it me, Jesus?

Waitress: when you guys are ready, we'll come and check on— Tina: what are you wearing?

It smells interesting.

Date: Glad you're asked actually.

This is my musk.

Tina: hmmm...

what???

Date: I just got done pumping some iron before this and want to gets some pheromones out there.

Tina: why?

Date: Well, research has shown that most females are attracted to the pheromones smell of an alpha.

Tina: Research has shown?

Okay, I'd like to see your citations for that.

I mean, do you really think we evolved the ability to smell so we could get some of this action over here?

But Ole Musk does bring up a good point.

Clearly, we have the ability to generate some interesting fragrances, but more importantly, we have the ability to detect them.

And that really makes me wonder, why do I smell?

Why am I like this?

Date: Yeah, so it's like pretty simple.

If you think about it.

Evolution gave us a sense of smell so that females could detect when they're in the presence of a real alpha.

Tina: Okay, this guy has no idea what he's talking about.

Evolution?

Simple?

To understand why humans might have evolved smell, we first need to understand what smell is and how it works.

Unknown: Yeah, so like, a lot of times when I'm bench pressing, I like to get down in there, get really close to the chest.

[muffled chatter] Tina: With smell, aka olfaction, it takes two to tango.

It involves an odor and the ability to sense that odor.

An odor is really just a particle that's volatile enough that it can travel up through our nostrils.

When the particles make it all the way to the back of our nose.

They hit a special patch of tissue called the olfactory epithelium, which contains olfactory receptor cells.

These are basically specialized neurons that act like nostril tastebuds.

They have branching projections that poke out into the mucus of your epithelium.

At the end of these wriggly boys are the receptors that are responsible for the function of funk.

Each of these receptors has a special shape that allows them to bind to particular particles.

Humans have around 400 Different olfactory receptors, but we can smell way more than just 400 smells because there isn't a one to one relationship between odor molecules and receptors.

Some receptors can fit multiple molecules.

But more importantly, smells are complex.

What we file away as a single smell actually triggers multiple receptors at a time.

For example— Cheese!

I love cheese.

Cheese isn't actually a single coherent smell.

It's a range of various combinations of chemical compounds that my brain has mentally filed away as cheese, aka, currently the only source of joy in my life.

It contains esters, aldehydes, methyl ketones, and sulfur compounds.

And each of these volatile compounds binds to a set of olfactory receptors.

But the magic doesn't stop there.

Once these receptor cells are triggered, they send a signal up to a meeting point where multiple olfactory neurons converge before collectively sending a message for your brain to decipher.

And like a smelly symphony, it's the combination of all these signals going off at once that creates the experience of smelling cheese.

But that experience can be different depending on your mental associations with cheese.

For example, I associate cheese with pure unadulterated joy and my childhood in Europe.

However, some of us don't have such a GOUDA memories of it.

Date: Yeah, I actually hate the smell of cheese because it reminds me of my cat who choked on a piece of cheese.

Tina: Oh my god, I'm so sorry.

Date: Oh that's not how she died.

She actually got hit by a car.

But she had trust issues.

And every time people brought cheese in the house, she would hits.

It's kind of stressful for me.

Tina: Speaking of childhood trauma, obviously, some of us have emotions entangled with certain aromatic associations.

But why?

Well, it goes back to what that smell signal does in your brain.

The olfactory message communicated to your brain is delivered at several stations.

Some of these regions of the brain, like the olfactory cortex are involved in identifying and categorizing smell.

Others, like the amygdala and hippocampus are involved in emotional processing, which is why smells can be associated with extremely happy or extremely sad events in your life.

Date: Mr. Whiskers.

I miss her so much.

Tina: But it's not as simple as your emotional state equals whether you like the smells around you or not.

For example, I might be in a fantastic mood and get a whiff of this guy over here and it will still be disgusting.

So, how does it work?

I've never met this guy before, so I can't blame him personally for a bad smell association.

But how did my brain decide that something smelled bad?

Do certain things inherently smell good or bad?

Or is that something that we learn?

Well, there's a whole area of study around the development of odor preferences and aversions.

What scientists have found is that there's a complex process involved in developing the full adult Rolodex of smells in relation to whether we should approach them or avoid them.

This series of determinations that smell helps us make: what is this smell?

Do I like it?

Should I avoid it?

Is actually incredibly important across the entire animal kingdom.

For example, African elephants can detect mines as they migrate through past war zones.

Wolves can use their noses to detect other animals more than a mile away.

And we've managed to train dogs to somehow smell everything from bombs to cancer.

And of course, some animals like moths can secrete and smell pheromones, and they use this to find mates.

But does this work for humans too?

A lot of people like this guy, believe humans release these magical molecules to somehow attract others to us.

But that's not how pheromones work.

Pheromones are chemicals that many animals can secrete in order to communicate with each other.

A lot of people associate pheromones exclusively with sexual attraction.

But different species can use them for different purposes.

They can signal anything from "This is my territory" to "Help me!"

But it's true that a lot of species use pheromones to say "hey, are you down to *wink wink*" Now what makes a pheromone different from a regular smell is that it elicits a particular kind of behavioral or physiological response.

So how do scientists identify a pheromone?

Well, it starts with an observation.

If scientists observe animal behavior they think might be caused by a smell signal, they start investigating.

They first isolate the compound they think might be responsible.

Then synthesize it and do a bunch of experiments to see whether it causes the same reaction that they first observed.

Many mammals and reptiles have a special structure called a vomeronasal organ, which is dedicated to sensing these pheromones and communicating that signal to the brain.

Funnily enough, the vomeronasal organ can be found in human fetuses, but it's completely atrophied and non functional by the time we become adults.

This isn't too surprising.

If you think about the relatively small role that smell plays for humans.

Compared to other species.

Like our primate cousins, we evolved to be a very visual species and for humans in particular, speech is an especially important trait.

If you think about it, visual impairment and blindness are considered disabilities as is hearing impairment and deafness.

The world is pretty hostile towards people with these kinds of disabilities the way most humans choose to communicate exclude such people from fully participating in many activities.

But what happens to people who have a diminished sense of smell or no sense of smell at all?

Well, this impairment, called anosmia, might not hinder their direct communication with other people.

But it turns out that even though smell isn't the star of the sensory show, it is a really important supporting character.

You know how ranke Milk smells when it goes bad?

You sniff that and you get the message loud and clear that this needs to go right down the drain, but someone dealing with anosmia might not and then they'd be dealing with food poisoning.

I don't know if you've ever smelled a gas leak, but that stuff stinks—like rotten eggs.

No, literally.

Gas companies add a chemical called mercaptan because natural gas actually doesn't have a smell.

So the stench is purposefully built in by humans as a warning signal.

But if you can't smell then you might not know until it's too late.

It's no wonder that anosmia is recognized as an invisible disability.

The way that smell serves as an alarm system is clearly important enough, but there are even more reasons why evolution has kept our sense of smell around.

You know how happy you get when you taste your favorite food.

It's a whole experience.

You smell the sweet aroma of your favorite pie.

Your mouth starts salivating and your body is ready for this.

Date: Oh my God, my mom used to make the best sweet potato pie when I was a kid you like pie?

Tina: love pie.

I make it all the time.

Date: *eating noises* Tina: Yeah.

Oh, I am so glad you're enjoying that.

I— Date: Really good.

Tina: You'd be surprised how much of your sense of taste is actually tied to smell.

Once the food is in your mouth, aroma molecules drift up through the retronasal passage near the back of your throat where they're treated the same as smells that came in through the nostrils.

Without smell some flavors, like cinnamon, actually wouldn't taste like cinnamon.

They'd just taste bitter.

And if we lose our ability to smell then eating becomes a sad and confusing experience, which is what happened to a lot of those who lost their sense of smell because of COVID.

The key role of smell and the sensory experience of food is what motivates a lot of us to eat and let's face it, food makes you happy.

Okay, so our sense of smell might not be able to help us pick out the alphas in the dating scene.

But it does add to every aspect and experience of our life.

You know what?

I might have been a little harsh on him.

After reflecting on this and why our ancestors evolved the sense of smell.

I really think I should you know, enjoy myself a little bit more.

Stop and smell the roses But damn.

These roses really smell like— Sorry back with a little bit of wine.

I'm so glad that you're enjoying yourself.

Weak!

Sorry That was great.