Poor human olfaction is a nineteenth century myth | Hacker News Reader

Poor human olfaction is a nineteenth century myth

ncbi.nlm.nih.gov

97 pointsBerislavLopac67 comments

For the last few hundred years, huge numbers of European-descended men took up tobacco. Moreover, cities were grossly polluted. I wonder if that affected the intuitions of scientists, who were mostly from such places. Maybe they really couldn’t smell very much.

Also, horse powered transport overwhelmed the senses by producing a lot of horse poop and dead horses. A million kg of horse poop was shoveled out of New York City every day.

My brain-teaser back-of-the-napkin skills tell me that's also the order of magnitude of human poop produced in NYC every day (I'd think its closer to 2-3 million kg)!

Though at least 50% of it doesn't happen on the streets.

Now let's do the estimate for San Francisco.

Also known as a Fermi estimation, in case you (or someone else) didn't know.

In school, I was preparing for a presentation about some electrical component we created. One of the questions was "how did you arrive at the proper input voltage". My buddy wrote down "guess and check?" - which I replaced with "Newton Iteration". That was one of my prouder moments

Did you actually use the derivative/first-order Taylor approximation to improve search speed though? My experience is that people instinctually default to some sort of binary search.

Also poor hygiene.

Fun fact: New York brownstones have raised levels because they were homes for the rich, who did not want to be at horse poop level.

When I was younger, I was walking through the NorCal redwoods with my family. It was a clear and crisp day, maybe 65F. I strolled ahead of the group by 30 or 40 feet, lost in thought, but enjoying the dim light and the smell of pine needles and duff. After a few minutes along the trail, I began to smell something else. It was...musky. Foreign to the place. A few minutes more and I realized I was smelling human.

Sure enough, we caught up to a slower group. After we passed them, the smell was gone. I'll never forget it.

You never been on bart?

I've heard many an anecdote of soldiers deployed for months in male-only settings who could smell that a woman had arrived on base. They weren't able to describe what they smelled, or how they knew it was a woman, but they just knew.

In the books of the former Navy SEAL Richard Marcinko (he sadly died in Dec 2021), it is repeatedly stressed that soldiers shouldn't use any cologne or indeed any perfumed soap, because these smells carry a long way in the wild. The plainest soap possible and that's it.

In About Face: The Odyssey of an American Warrior (1989), David Hackworth mentions about being on patrol in the Korean war:

None of us used repellent (Chinks could smell it as easily as after-shave, soap, tobacco, and toothpaste); we couldn’t slap at them (noises traveled loud and far at night). So we waited and reluctantly contributed our blood.

and about poor discipline in Vietnam:

Guys were using soap, toothpaste, and shaving cream before operations. They were smoking and wearing mosquito repellent on patrol.

After taking up foraging for mushrooms in the wild, I've become aware of so many more smells. But most of them I can't name or tell the origin of.

Smell is an underrated aspect of foraging. Many people start out focusing just on appearance, but smell is a big deal even with mushrooms.

I used to occasionally fill in for my professor to run labs in a biology class, and I'd encourage the students to smell and such saying, "you do science with all of your senses."

I went on a weeks-long sailing expedition as a teenager and realized after my first couple days at sea that I could smell land from over the horizon.

If we were passing downwind of a landmass I could smell it even if I couldn't see it!

Both trees and regular dirt have a smell that carries for miles and miles and when you've been on a fiberglass boat with no trees and dirt for days the smell really, really, stands out.

I imagine that ancient maritime explorers, at sea in the vast oceans for weeks not days, would have been able to smell remote forested and guano-covered islands for hundreds of miles.

Oliver Sacks came to that conclusion:

https://en.wikipedia.org/wiki/The_Man_Who_Mistook_His_Wife_f...

> "The Dog Beneath the Skin", concerning a 22-year-old medical student, "Stephen D.", who, after a night under the influence of amphetamines, cocaine, and PCP, wakes to find he has a tremendously heightened sense of smell.[7] Sacks would reveal many years later that he, in fact, was Stephen D.[8]

Is that reproducible? If I do meth, cocaine and PCP together, will I forever have superhuman sniffing powers?

You may perceive yourself to have superhuman sniffing powers, depending on how late into the morning your bender goes.

When I take stimulant medication for ADHD it makes my sense of smell more acute (sometimes to a noxious degree, unfortunately; I already sense smells more than most people even without the meds). It seems to be a thing, though. I’ve heard similar remarks from other folks with ADHD.

Just cause yourself to have a migraine, or go on oxygen.

Probably a hallucination.

In one of his memoirs, Feynman empirically tested his own sense of smell and came to the same conclusion.

Could you recommend one of his books? I’d like to read some Feynman this year but I have no idea where to start.

"Surely you're joking, Mr Feynman" I think is the most famous and is quite enjoyable.

Yes, but what does it smell like?

Depends on who is touching it.

Also I recommend “Genius” by James Gleick which is a fantastic biography of him.

Here’s an excerpt from Surely You’re Joking, Mr Feynman! If anyone’s curious:

“Then I looked at the bookshelf and said, ‘Those books you haven’t looked at for a while, right? This time, when I go out, take one book off the shelf, and just open it—that’s all—and close it again; then put it back.’ So I went out again, she took a book, opened it and closed it, and put it back. I came in—and nothing to it! It was easy. You just smell the books. It’s hard to explain, because we’re not used to saying things about it. You put each book up to your nose and sniff a few times, and you can tell. It’s very different. A book that’s been standing there a while has a dry, uninteresting kind of smell. But when a hand has touched it, there’s a dampness and a smell that’s very distinct. We did a few more experiments, and I discovered that while bloodhounds are indeed quite capable, humans are not as incapable as they think they are: it’s just that they carry their nose so high off the ground!”

When I was a kid my doctor discovered that I had planned to join the military, and was devastated as he had imagined me to become a surgeon or physicist, so he gave me Surely You're Joking, Mr Feynman as a gift on my 18th birthday - as a way to convince me the military was a bad idea (somehow, I still don't understand why he thought this would work). Anyway, I read it in one weekend, and remember the part you're quoting. I learned things about attention to detail in that book that are very hard to teach.

Isn't there another story about how he broke open some safes? I'm remembering as much, at least. I need to read it again. I'm double that age now, so it's about that time.

What I remember is a story about a file cabinet that he wanted unauthorized access to, not exactly a safe but similar.

Yeah, during the Manhattan Project he broke into everyone’s locked filing cabinets to prove that the security measure was basically for show.

A lot of smelling requires your nose to actually be next to the floor. We don't exactly do that anymore.

Seems like an advantage to be able to smell prey and predator. Why didn't we evolve (ie naturally select) humans with stronger noses.

Why did dogs not evolve better eyes?

Because they did not start off on their hind legs, and lose vision benefits by getting closer to the ground

Doesnt that answer your question? If humans vision benefits are so good, and being close to the ground is bad, then the need for a strong sense of smell is greatly reduced.

I've had dogs for a while, and at least for my dogs they use their eyes and ears more than their noses. I've tested this a few times with steak, and using their nose is a last resort tactic.

It's likely an optimization: if you see your prey/steak, you don't need smell to follow it.

Brains (not just dogs') are full of such optimizations.

Also, some breeds of dog are more behaviorally driven by scent or vision, and the morphology of their nose and face matter too.

Some dogs are "sighthounds", the greyhound being the classic example, which primarily orient on vision and use speed to hunt, some are "scent hounds" the bloodhound being sort of the canonical example, which use scent tracking and endurance rather than speed.

I've been doing nose training with my dog. She's got the idea of the game and she's definitely quicker to use scent, but still prefers to just look.

She acts like it's a lot more effort to sniff something out. Maybe in a home environment there's too many other scents and she has to be right on top of the treat to find it? Who knows.

Because they're carnivores. Mammals evolved in the Jurassic as nighttime creatures, because warm blood gave them an advantage over reptiles, and they lost color vision in exchange for better nighttime vision. Once dinosaurs disappeared mammals no longer had to restrict themselves and could occupy new niches. That's when primates got color vision back, to be able to distinguish ripe fruits.

Cue to post a link to the Quanta magazine article on how Chickens have dinosaur eyes, and didn’t have to evolve to night time use and back like mammals:

https://www.quantamagazine.org/hyperuniformity-found-in-bird...

Now if the genetics could be transferred back to mammals things might look different, assuming the brain and optic nerve are still up to it.

Because humans are social animals (with a powerful visual cortex and able to walk a lot).

Nothing to do with the "lone wolf" prey/predator idea.

Too bad that nowadays our jaw development is so compromised and allergies so common that just about all of us have deviated septums and nasal cavities too narrow and misshapen for enough inhaled air to reach the right receptors.

I'm, for one, barely capable of smelling anything, heh.

Interesting. I have chronic allergies and narrow nasal cavities, but my sense of smell is very sharp. In fact I smell a lot of things I really don’t want to just about every day.

I can smell my family members across rooms, smell dog poo that wasn’t picked up on the sidewalk long before I walk close to it, smell fumes from traffic very easily.

Allergies dampen it but I can smell more than I need to all the time.

There’s one weird part though. I can’t seem to smell pee very well. When my kids were smaller and would get pee on stuff I’d never notice. Clothing, bedding, etc. To this day I have no idea why I can smell someone’s dirty hands from several feet away but I can’t smell pee. Everyone can smell pee, I think.

As a result I always assume I probably smell like pee but have no way of knowing.

If you contemplate all the possible reasons why you might smell like pee, you will have your answer.

I mean, when you have tiny kids and a hard time smelling pee, it’s tougher to tell. Kind of like you won’t always realize you’ve got baby puke trailing down your shoulder — they’ll get you by surprise.

Unless there's something wrong with you, urine is sterile. And unless you ate stuff that smells (sulphur compounds in asparagus for example) your piss doesn't really smell after exiting your bladder. It only becomes smelly after some time, when bacteria have had the chance to work on it. Or when you're super dehydrated and you're pissing an orange slurry.

My smell is pretty acute, but little splashes of urine from the kids are often almost scent-less. Only when they walk around for a while after small accidents do things get noticeably pissy smelling.

Do you also not smell aged, rancid piss in the frequently visited (and messily used) urinals at a bar or highway gas station?

This is a misconception, urine doesn't have many microorganisms, but it isn't quite sterile. And, strange, I find that despite a very weak sense of smell, I can smell mine if I'm even a little dehydrated and it isn't clear.

Do you breath through your nose or mouth when you sleep? Often people with deviated septums will mouth-breath.

I’m a severe mouth breather. Both literally and figuratively.

Congratulations, you have sleep disordered breathing. Get a sleep study, ideally one that scores UARS and not only sleep apnea.

Oh wow that sounds absurd. I have a friend with extremely strong BO, and I need to be right next to him to notice even if he's not showered in a week.

The notion of smelling people across rooms... it's as freaky to me as if you'd told me some people have x-ray vision.

I wonder if your particular case of nasal cavity just happens to have topology that delivers air to the olfactory portion of it very effectively.

This funny little thing cleaned my sinuses so thoroughly that I no longer carry tissues around. There is simply no need.

https://www.mayoclinic.org/diseases-conditions/common-cold/e...

I do this several times a week as a prevention. The learning curve is ugh, but once the nose is clean, it is an almost enjoyable experience.

Also, it seems to snuff out beginning colds really efficiently, though not 100 per cent reliably.

I would recommend using nasal saline spray instead. The chance of nigleria fowleri is tiny, but definitely not worth it.

The worst documented outbreak was actually in Czechoslovakia:

1056/NEJM196606302742605. PMID 5939846. - Červa, L.; Novák, K. (April 1968). "Ameobic meningoencephalitis: sixteen fatalities". Science. 160 (3823): 92.

That said, I feel fairly safe, because I

a) run the water through a fine filter < 1 micron first,

b) boil it anyway, just to be sure,

c) these amoebas don't like cold running water and tend to live in warmer, stagnant waters only, so a typical municipal water system won't be infested.

I had terrible allergies as a kid. I grew up in a city and would go back to farms in South Dakota and Iowa to see family, and would be miserable.

I then joined the military, and went to certain schools where you are not actually allowed to take allergy meds for safety reasons. I had an allergy attack (some kind of crazy histamine reaction) that honestly made me think I was going to collapse. Woke up the next morning, and I've had no allergy symptoms for about a decade now.

This is to say ... go outside.

I’m glad that worked for you, but for some people with allergies each attack can make the allergy worse, as the immune system sensitizes itself to the allergen in the presence of inflammation.

One treatment for allergies is exposure, but that is done using extremely small doses to allow the immune system to “see” the allergen without inflammation and thus lessen the response.

https://aip.scitation.org/doi/10.1063/1.5121155

A vibrational theory of smell...

Is olfaction a quantum thing?

Well, yes. The details of biochemical interactions involved in olfaction involve a lot of quantum mechanics, which also affects the way molecules vibrate.

But this is not some sort of "quantum woo" or mysterious thing... it's just quantum mechanics being quantum mechanics, which is, after all, the dominant and most correct theory of how small things perform in the real world, not some utterly mysterious incomprehensible magic.

So... of course it's a quantum thing. Everything's a quantum thing, seeing as how relativity, the other dominant and most correct theory of how things perform, is not generally relevant to energy regimes you live in. Things are not specially distinguished by being "quantum things". The surprise would be to find something that isn't. (Which could conceivably include gravity at this point in time, though I think that even if we can't prove it's quantized at this juncture in time physicists would be stunned to discover it wasn't.)

It should also be observed that "quantum" does not mean any sort of meaningful "entanglement" mystery is going on.

Frankly we'd all have a more accurate view of the world if the word "quantum" was associated with "boring" and "engineering" rather than "mysterious". It isn't that there isn't a bit of mystery there, it's just it's mostly boring and engineering with a tinge of mystery, rather than a whole big box of mystery. It can't be that mysterious if you can pop numbers in one side, run a mathematical crank, and get very accurate predictions out the other.

thanks, I'll take a tinge of mystery :)

“My dog has a tiny olfactory bulb.”

“How does he smell?”

“Awful.”

A few years ago I had a medical procedure that entailed not eating for 2 or 3 days - just drinking water. By the end of that fasting period, my sense of smell was immeasurably heightened, and could definitely smell the differing fragrance of other humans walking along the streets.

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