6 ms·

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.
  - im3w1l 7y ago
    Lactase is just retaining a juvenile trait. And blonde gene is producing less of a chemical. These are fairly easy things for evolution to solve.
  - vikramkr 7y ago
    Lactose is just keeping a juvenile gene active and is a matter of life and death - the blonde gene is a single mutation that can take root from a genetic bottleneck. AMD even lactose isn't universal. Just being able to smell that soil is moist (instead of looking at it, or touching it...) is not as powerful a survival advantage as lactase or sickle cell or some of those life and death mutations for food or malaria resistance.
    - thatcat 7y ago
      I think there is more information being transmitted than just that the soil is moist. The soil is lightly moist + highly porous + has high levels of microbiological activity which are the optimal conditions for seed germination. Consider that inedible seeds could act as a preserved food that could be germinated and edible in only a few days with no energy input by hunter gatherers who were known to gather and eat seeds - giving more like 70-80k years for Petrichor to be interpreted by humans as an attractive smell. The plant growth/food hypothesis doesn't make sense to me because this signal is timing specific and the timing isn't related fruiting periods. Also growing plants have their own smells so why would an indirect smell be preferred? Also, consider the evolutionary path of associating a smell doesn't require any protein production or chemical changes - only neurological ones. This shows that mice can inherit the ability fear certain smells from their parents. It's possible that it could happen epigenetically in humans as well considering the significant changes in taste and smell sense experienced in ones lifetime. [0]https://www.smithsonianmag.com/smart-news/baby-mice-can-inherit-fear-of-certain-smells-from-their-parents-180948096/ https://www.smithsonianmag.com/smart-news/baby-mice-can-inhe... [edit: added source]
    - gumby 7y ago
      FWIW the lactase gene is not a matter of life or death — people lived at high latitude for millennia before it evolved. When it happened though it clearly was selected for. Most genes don’t select Individually on a life-or-death basis, especially in long-living species as its time scale is wrong (slight exception: pinch points like pandemics). It merely adds a bit of evolutionary advantage aggregated with all others. Thus, for example, your sickle cell example: it’s pervasive but hardly universal among its carrier population even though that population was until very recently all exposed to the same (malarial) risk. In any case my point was that mutations certainly do evolve and stabilize within the span of human civilization (however one might define that). Evolution is a big, parallel, path-dependent process indifferent to which particular kinds of selection (physical or social, endemic or peculiar) happen to favor reproduction.
- folli 7y ago
  Fertile grounds are also helpful for foraging.
  - vikramkr 7y ago
    That would make far more sense than being tied to farming. Ability to detect where to move to to forage for food, select for that evolutionary pressure over millions of years beginning from our ancestor species, etc
- fit2rule 7y ago
  >Farming developed so recently The jury is still out on how recently agriculture was developed by human cultures. We are still discovering our history - its not entirely clear that it is as recent as Western academia is capable of demonstrating, empirically .. Take, for example, the as-yet under-explored evidence in Australia that agriculture extends tens of thousands of years further into our past than we currently acknowledge. Its entirely feasible we developed a sense of soil as a consequence of our technological use of it.
  - vikramkr 7y ago
    Right ... we're still talking on the scale of tens of thousands of years. That's a blink of an eye evolutionarily. Evolving complex smell and behavior responses to something like being able to tell what soil is good for planting seeds (when, remember, we can just look at and feel the soil! Evolution isn't some force that invents new features in life for every minuscule need- natural selection is the survival of the good enough) in just a few tens or hundreds of thousands of years across the entire population is not feasible. Consider also that farming didn't just begin once, and presumably hunter gatherers can also smell petrichor. If it was tied to farming (and somehow was a life or death situation) we'd see that trait with a distribution similar to lactose tolerance, not as universal as the ability to smell petrichor.
    - fit2rule 7y ago
      >tens of thousands of years. That's a blink of an eye evolutionarily. I dunno about that. It seems we can gain major advances in evolution over just a few generations. Look, for example, at the rapid changes that have occurred in the West over the last century, particularly with regards to sexual maturation of healthier classes. This is clear evidence that evolution can happen a lot faster than we might imagine, even so. I don't find it difficult at all to imagine that the human genome alters itself over a period of, even a thousand years, in order to respond to the changing environment. We see examples of these shorter orders of magnitude throughout our history ..

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.
- im3w1l 7y ago
  Lactase is just retaining a juvenile trait. And blonde gene is producing less of a chemical. These are fairly easy things for evolution to solve.
- vikramkr 7y ago
  Lactose is just keeping a juvenile gene active and is a matter of life and death - the blonde gene is a single mutation that can take root from a genetic bottleneck. AMD even lactose isn't universal. Just being able to smell that soil is moist (instead of looking at it, or touching it...) is not as powerful a survival advantage as lactase or sickle cell or some of those life and death mutations for food or malaria resistance.
  - thatcat 7y ago
    I think there is more information being transmitted than just that the soil is moist. The soil is lightly moist + highly porous + has high levels of microbiological activity which are the optimal conditions for seed germination. Consider that inedible seeds could act as a preserved food that could be germinated and edible in only a few days with no energy input by hunter gatherers who were known to gather and eat seeds - giving more like 70-80k years for Petrichor to be interpreted by humans as an attractive smell. The plant growth/food hypothesis doesn't make sense to me because this signal is timing specific and the timing isn't related fruiting periods. Also growing plants have their own smells so why would an indirect smell be preferred? Also, consider the evolutionary path of associating a smell doesn't require any protein production or chemical changes - only neurological ones. This shows that mice can inherit the ability fear certain smells from their parents. It's possible that it could happen epigenetically in humans as well considering the significant changes in taste and smell sense experienced in ones lifetime. [0]https://www.smithsonianmag.com/smart-news/baby-mice-can-inherit-fear-of-certain-smells-from-their-parents-180948096/ https://www.smithsonianmag.com/smart-news/baby-mice-can-inhe... [edit: added source]
  - gumby 7y ago
    FWIW the lactase gene is not a matter of life or death — people lived at high latitude for millennia before it evolved. When it happened though it clearly was selected for. Most genes don’t select Individually on a life-or-death basis, especially in long-living species as its time scale is wrong (slight exception: pinch points like pandemics). It merely adds a bit of evolutionary advantage aggregated with all others. Thus, for example, your sickle cell example: it’s pervasive but hardly universal among its carrier population even though that population was until very recently all exposed to the same (malarial) risk. In any case my point was that mutations certainly do evolve and stabilize within the span of human civilization (however one might define that). Evolution is a big, parallel, path-dependent process indifferent to which particular kinds of selection (physical or social, endemic or peculiar) happen to favor reproduction.
folli 7y ago
Fertile grounds are also helpful for foraging.
- vikramkr 7y ago
  That would make far more sense than being tied to farming. Ability to detect where to move to to forage for food, select for that evolutionary pressure over millions of years beginning from our ancestor species, etc
fit2rule 7y ago
>Farming developed so recently The jury is still out on how recently agriculture was developed by human cultures. We are still discovering our history - its not entirely clear that it is as recent as Western academia is capable of demonstrating, empirically .. Take, for example, the as-yet under-explored evidence in Australia that agriculture extends tens of thousands of years further into our past than we currently acknowledge. Its entirely feasible we developed a sense of soil as a consequence of our technological use of it.
- vikramkr 7y ago
  Right ... we're still talking on the scale of tens of thousands of years. That's a blink of an eye evolutionarily. Evolving complex smell and behavior responses to something like being able to tell what soil is good for planting seeds (when, remember, we can just look at and feel the soil! Evolution isn't some force that invents new features in life for every minuscule need- natural selection is the survival of the good enough) in just a few tens or hundreds of thousands of years across the entire population is not feasible. Consider also that farming didn't just begin once, and presumably hunter gatherers can also smell petrichor. If it was tied to farming (and somehow was a life or death situation) we'd see that trait with a distribution similar to lactose tolerance, not as universal as the ability to smell petrichor.
  - fit2rule 7y ago
    >tens of thousands of years. That's a blink of an eye evolutionarily. I dunno about that. It seems we can gain major advances in evolution over just a few generations. Look, for example, at the rapid changes that have occurred in the West over the last century, particularly with regards to sexual maturation of healthier classes. This is clear evidence that evolution can happen a lot faster than we might imagine, even so. I don't find it difficult at all to imagine that the human genome alters itself over a period of, even a thousand years, in order to respond to the changing environment. We see examples of these shorter orders of magnitude throughout our history ..