6 ms·

Wonder why the smell is considered pleasant to humans (especially freshly/lightly wet soil). Similarly, what're the secrets to the amazing fresh spring/summer

• merpnderp 7y ago
  Perhaps it's a good clue on where to plant crops?
  • dTal 7y ago
    Agriculture 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 ago
      There are other relatively recent adaptations due to farming, some of which are quite complex, like lactose tolerance.
      • dodobirdlord 7y ago
        Adult 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 ago
        Agriculture and pastoralism are 2 different things.
• doctoboggan 7y ago
  Just 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 ago
    That 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 ago
    Perhaps it indicates that the soil is at an optimal moisture level for planting/ germinating a seed.
    • vikramkr 7y ago
      Farming 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 ago
        Not 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 ago
  This 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 ago
    Similarly 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 ago
      That 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 ago
        Probably 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 ago
      Probably more correlated to the survival aspect of being able to smell a thunderstorm and take shelter.
    • MaxBarraclough 7y ago
      But that's nowhere near 5 parts per trillion (0.000005 ppm).
  • deleted 7y ago
• Jestar342 7y ago
  Wet soil indicates there's a nearby source of (potentially potable) water.
• hoorayimhelping 7y ago
  Wet, 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 ago
  Evolution 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 ago
    This 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 ago
      ok. 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 ago
    Because 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.