5 ms·

The origin of homochiral building blocks (amino acids, sugars) is certainly an old mystery. But it doesn't seem to be a very deep one. By that I mean that there

by aazaa 6y ago

The origin of homochiral building blocks (amino acids, sugars) is certainly an old mystery. But it doesn't seem to be a very deep one. By that I mean that there are many physical processes that could have initially led to a small preference. Natural selection then would do the rest. The deeper mystery is how self-replicating chemical systems ever came about in the first place. There are several fairly steep hurdles to overcome, and so far nobody has put forward a compelling, testable hypothesis leading from the "primordial soup" to anything even distantly resembling the simplest organisms.

api 6y ago
There are many hypotheses but they are quite hard to test. The problem is that any such process is likely to have involved millions of years (at a minimum) of essentially random search among initial building blocks before something "takes." How do you even try to replicate that? We could perhaps fast forward it in a lab but that is going to make it contrived. The best we can probably do is to work backward from the simplest life to a credible model of prebiotic replicating molecular systems and then back from there to random organics plus energy. Then try to do isolated experiments to assign probability bounds and then try to estimate time and probability. This is not a true replication or a direct observation but it could at least provide a credible model.
- TeMPOraL 6y ago
  I remember a coherent-sounding (to a somewhat smart layman) theory being presented in "The Vital Question". It involved alkaline vents (like these: [0]). As I remember it, the idea was that the nonviolent flow of matter and the porous rock of the vent created a natural chemical reactor, where gunk could accumulate in the pores, until it slowly chanced into a primitive pump, primitive membrane and primitive division; eventually, some of that gunk learned how to close a membrane around itself, with stuff from the alkaline vent on the inside, and could now survive out in the open, continuously pumping to keep the gradient. Evolution continued from there. -- [0] - https://en.wikipedia.org/wiki/Lost_City_Hydrothermal_Field https://en.wikipedia.org/wiki/Lost_City_Hydrothermal_Field
sova 6y ago
Is it not pure speculation to assume that the world was present before living beings inhabited it? Who made these observations of a purely physicalist realm that predates beings with awareness? It may be true, but its unconfirmable, so we have to ask questions about what we can confirm. Chirality in the present is confirmable. A world made of physical matter and mind is confirmable. But strong questions about ontological declarations of life from purely physicalist material speculative histories are not only hard to answer, they assume more than they reveal. Edit: must have hit a nerve
- deleted 6y ago
  [deleted]
- dvt 6y ago
  I don't think you hit a nerve; your post is not only confusing, but it seems wrong. > Is it not pure speculation to assume that the world was present before living beings inhabited it? You need to carefully define terms here. What do you mean by "world," what do you mean by "living beings," and what do you mean by "inhabited." In any case, the answer to the question you pose is almost certainly answerable in the negative. > But strong questions about ontological declarations of life from purely physicalist material speculative histories are not only hard to answer, they assume more than they reveal. I'm not a materialist, but this isn't correct. In fact, a major criticism of physicalism is that it's too reductive -- not that it has no explanatory power. It has a lot of it; that's partly why most professional philosophers are materialists.
- ridgeguy 6y ago
  Nobody's making that assumption. It's a hypothesis. All evidence we have is consistent with a "world being present before living beings inhabited it". Therefore the hypothesis is not disproved, which is all science ultimately says about facts.
  - sova 6y ago
    Chirality is either an underlying property of biological life, or an epigenetic (so-to-speak) result from having a Spinning Something and then throwing Life into it. Reality itself could have a spin or orientation and therefore Biological Life would be subservient to such. In my opinion long-term adaptations have about as much pertinence to chirality as it does to magnetism. Either it turns or it doesn't, it doesn't slowly decide to over millions of years.
kleer001 6y ago
RNA-world seems pretty compelling to me. Self replication and catalysis. That sounds like enough to go on.
chongli 6y ago
how self-replicating chemical systems ever came about in the first place I don't think it's too much of a stretch to say that it's pretty much inevitable after Miller-Urey [1]. This process produces so much complexity from such simple ingredients. I think if we could travel to distant stars we would find simple, single-celled life all over the place. The tougher question is why we haven't found any intelligent life yet [2]. [1] https://en.wikipedia.org/wiki/Miller–Urey_experiment https://en.wikipedia.org/wiki/Miller–Urey_experiment [2] https://en.wikipedia.org/wiki/Fermi_paradox https://en.wikipedia.org/wiki/Fermi_paradox
- taneq 6y ago
  We've only been looking for a gnat's blink, astronomically speaking. Once we've searched for a couple of million years, then we'll have a bit more data to draw conclusions from.

by aazaa 6y ago

api 6y ago

There are many hypotheses but they are quite hard to test. The problem is that any such process is likely to have involved millions of years (at a minimum) of essentially random search among initial building blocks before something "takes." How do you even try to replicate that? We could perhaps fast forward it in a lab but that is going to make it contrived. The best we can probably do is to work backward from the simplest life to a credible model of prebiotic replicating molecular systems and then back from there to random organics plus energy. Then try to do isolated experiments to assign probability bounds and then try to estimate time and probability. This is not a true replication or a direct observation but it could at least provide a credible model.

TeMPOraL 6y ago
I remember a coherent-sounding (to a somewhat smart layman) theory being presented in "The Vital Question". It involved alkaline vents (like these: [0]). As I remember it, the idea was that the nonviolent flow of matter and the porous rock of the vent created a natural chemical reactor, where gunk could accumulate in the pores, until it slowly chanced into a primitive pump, primitive membrane and primitive division; eventually, some of that gunk learned how to close a membrane around itself, with stuff from the alkaline vent on the inside, and could now survive out in the open, continuously pumping to keep the gradient. Evolution continued from there. -- [0] - https://en.wikipedia.org/wiki/Lost_City_Hydrothermal_Field https://en.wikipedia.org/wiki/Lost_City_Hydrothermal_Field

sova 6y ago

Is it not pure speculation to assume that the world was present before living beings inhabited it? Who made these observations of a purely physicalist realm that predates beings with awareness? It may be true, but its unconfirmable, so we have to ask questions about what we can confirm. Chirality in the present is confirmable. A world made of physical matter and mind is confirmable. But strong questions about ontological declarations of life from purely physicalist material speculative histories are not only hard to answer, they assume more than they reveal. Edit: must have hit a nerve

deleted 6y ago
[deleted]
dvt 6y ago
I don't think you hit a nerve; your post is not only confusing, but it seems wrong. > Is it not pure speculation to assume that the world was present before living beings inhabited it? You need to carefully define terms here. What do you mean by "world," what do you mean by "living beings," and what do you mean by "inhabited." In any case, the answer to the question you pose is almost certainly answerable in the negative. > But strong questions about ontological declarations of life from purely physicalist material speculative histories are not only hard to answer, they assume more than they reveal. I'm not a materialist, but this isn't correct. In fact, a major criticism of physicalism is that it's too reductive -- not that it has no explanatory power. It has a lot of it; that's partly why most professional philosophers are materialists.
ridgeguy 6y ago
Nobody's making that assumption. It's a hypothesis. All evidence we have is consistent with a "world being present before living beings inhabited it". Therefore the hypothesis is not disproved, which is all science ultimately says about facts.
- sova 6y ago
  Chirality is either an underlying property of biological life, or an epigenetic (so-to-speak) result from having a Spinning Something and then throwing Life into it. Reality itself could have a spin or orientation and therefore Biological Life would be subservient to such. In my opinion long-term adaptations have about as much pertinence to chirality as it does to magnetism. Either it turns or it doesn't, it doesn't slowly decide to over millions of years.

kleer001 6y ago

RNA-world seems pretty compelling to me. Self replication and catalysis. That sounds like enough to go on.

chongli 6y ago

how self-replicating chemical systems ever came about in the first place I don't think it's too much of a stretch to say that it's pretty much inevitable after Miller-Urey [1]. This process produces so much complexity from such simple ingredients. I think if we could travel to distant stars we would find simple, single-celled life all over the place. The tougher question is why we haven't found any intelligent life yet [2]. [1] https://en.wikipedia.org/wiki/Miller–Urey_experiment https://en.wikipedia.org/wiki/Miller–Urey_experiment [2] https://en.wikipedia.org/wiki/Fermi_paradox https://en.wikipedia.org/wiki/Fermi_paradox

taneq 6y ago
We've only been looking for a gnat's blink, astronomically speaking. Once we've searched for a couple of million years, then we'll have a bit more data to draw conclusions from.