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Soil gets its smell from bacteria trying to attract invertebrates
- radicaldreamer 7y agoWonder why the smell is considered pleasant to humans (especially freshly/lightly wet soil). Similarly, what're the secrets to the amazing fresh spring/summer rain smell...
- merpnderp 7y agoPerhaps it's a good clue on where to plant crops?
- dTal 7y agoAgriculture is unlikely to be the reason it evolved, as agriculture is only a few tens of thousands of years old. However fertile soil is also a good sign if you are a hunter/gatherer; it implies rich plant life, and therefore things to gather and maybe also things to hunt.
- empath75 7y agoThere are other relatively recent adaptations due to farming, some of which are quite complex, like lactose tolerance.
- dodobirdlord 7y agoAdult lactose tolerance isn't much of a change, because humans were already lactose tolerant as infants. The evolutionary complexity to keep producing enzymes into adulthood is minor compared to the complexity of evolving those enzymes to begin with.
- _emacsomancer_ 7y agoAgriculture and pastoralism are 2 different things.
- doctoboggan 7y agoJust speculating, but humans could be attracted to the smell because it indicates fertile soil that would be more likely to have fruits for foraging.
- keenmaster 7y agoThat is the most likely reason in my opinion. Usually, when something in our natural environment is pleasant to our senses, that's because it's a good thing from an evolutionary standpoint. Vice-versa with unpleasant things.
- thatcat 7y agoPerhaps it indicates that the soil is at an optimal moisture level for planting/ germinating a seed.
- vikramkr 7y agoFarming developed so recently that its difficult to imagine a scenario where the ability to be attracted to an area that is good for sowing crops was such a strong life or death driver (as opposed to just being able to poke the soil to measure moisture) that we became that sensitive to petrichor that quickly. There were some other hypotheses in the thread about the scent indicating a potential abundance of plant growth and food, which could make sense. Especially if some of our closer relatives like apes have the same ability to sense petrichor- it could have been selected for over millions of years
- gumby 7y agoNot clear: both the lactase gene and blonde gene are pretty recent (last 2-20 ky -- an ice age ago or less). If agriculture, especially pre-fixed-location agriculture, is a significant evolutionary advantage (which I think most people think it is) then it's possible the evolutionary pressure for this mutation would be quite strong and its carriers would be overrepresented in the world's population.
- 7y ago
- konz 7y agoThis is called Petrichor and the human nose is indeed hyper sensitive to it (5 parts per trillion). https://en.m.wikipedia.org/wiki/Petrichor https://en.m.wikipedia.org/wiki/Petrichor
- tomxor 7y agoSimilarly and linked in the same article, the human nose is sensitive to ozone in as little as 0.1 ppm, and it seems an unlikely coincidence that it starts to become hazardous to respiratory tissue above this concentration.
- duskwuff 7y agoThat seems like a stretch to me. Sources of hazardous concentrations of ozone are generally technogenic in nature -- the concentrations produced by lightning in the troposphere are far too low to pose any real danger. As such, there's no reason that humans (or any organisms) would have evolved to specifically detect that.
- tomxor 7y agoProbably not directly, but the mechanisms we evolve are generalized to some degree, i.e they often end up being useful for things our ancestors never encountered. Perhaps the method by which we smell give us a similar sense for some similarly hazardous molecules. According to the wiki O3 smells much like Chlorine, they are both highly oxidizing which is why they can be hazardous.
- bduerst 7y agoProbably more correlated to the survival aspect of being able to smell a thunderstorm and take shelter.
- MaxBarraclough 7y agoBut that's nowhere near 5 parts per trillion (0.000005 ppm).
- deleted 7y ago
- Jestar342 7y agoWet soil indicates there's a nearby source of (potentially potable) water.
- hoorayimhelping 7y agoWet, fertile soil indicates two beneficial things for certain: water, and fertility. The presence of these strongly implies other things we like: a food web and a source of energy and shelter.
- ggm 7y agoEvolution doesn't have to switch off things of no use, but no direct burden. There is no inherent upside statistically in the mating game to "not" being able to smell soil, so it would be inherently "wasteful" in gene terms to turn this off. We might have carried this up from simpler forms who benefited from it in positive gene-sense. We won't neccessariy loose it, unless there is a statistically measurable upside benefit, or something like energy consequences.
- RhodesianHunter 7y agoThis seems very unlikely given that most of the various structures and pathways involved in smell in humans don't exist in our earliest (in the bacteria sense) ancestors. It seems far more likely to be a positive associating due to a higher likelihood of finding growing food.
- ggm 7y agook. so at some point we acquired it. it must be either very old, or recent. in either case, the fact it confers at best marginal evolutionary benefit, suggests that it is not strongly linked to what we are as humans, and its net cost to us persisting in the genome confers no disadvantage or, is coupled in gene terms to other attributes (sense of smell in general) which are sufficiently beneficial, it will not disappear
- im3w1l 7y agoBecause of mutations, anything that isn't used will tend to stop working. On the other hand the "tech debt" that comes with everything accidentally relying on everything else working a certain way, is a pressure to conserve past behavior.
- hirundo 7y agoSo soil bacteria smell good to invertebrates for the same reason that fertile/virile humans smell good to their sexual complements: it helps to distribute their genes.
- autokad 7y agoI am a little confused, am I reading this correctly? - the smells are coming from streptomyces - springtails are attracted to the smells - springtails feed on the streptomyces therefore the conclusion is not that bacteria are attracting invertebrates with the smell, but rather the invertebrates evolved to smell something they feed on? Did I read this wrong?
- yipbub 7y agoDid bees evolve to find nectar or flowers evolve to attract bees? A lot of both.
- PeterisP 7y agoProducing that smell is 'costly' and doesn't seem to have any other use, so if it wouldn't benefit the bacteria then they would be expected to evolve to not manufacture these chemicals.
- mekoka 7y agoIt's hard to tell which is which and it's probably a bit of both. I don't really understand why whenever the living nature is being explained, it's done in a way that attributes to some design what really belongs to an accident of evolution. Species develop traits continuously and in a chaos, every individual is a mutant, then environmental pressure determines combinations that are most suited to reoccur (through reproduction). In this case two species found each other. Maybe a few springtails had the genes to detect the smell. Of those, a few found it pleasant, it could be that others didn't. Maybe a few streptomyces had the genes to produce the smell. A happy accident that allowed both these genetic traits to endure environmental pressure.