3 ms·

Life arising many times in parallel ought to have given rise to multiple trees of life with mutually incompatible biochemistry. Yet, overall life speaks about t

by samus 4y ago

Life arising many times in parallel ought to have given rise to multiple trees of life with mutually incompatible biochemistry. Yet, overall life speaks about the same genetic language, and most things work very similar to each other. Life could still have indeed arisen multiple times, however, it probably either merged or got supplanted by its competitors. Life is simply too pervasive to allow for anything else. It would also immediately out-compete any newly arising life. There is some evidence that things like the genetic code, the choice of RNA/DNA nucleotides, and the set of the 20 aminoacids aren't really random. That would not rule out life arising multiple times, but the likelihood that it merged with other lineages would be even higher. Short summary: https://www.science.org/content/blog-post/why-these-amino-acids-anyway https://www.science.org/content/blog-post/why-these-amino-ac... . A more in-depth paper: https://www.sciencedirect.com/science/article/abs/pii/S0378111900004765?via%3Dihub https://www.sciencedirect.com/science/article/abs/pii/S03781...

akiselev 4y ago
There are a lot of microbes that are unculturable to this day and to my knowledge, no one has really done a proper investigation to see if the universal metabolic molecules like, for example, the hydrogen carriers NAD+/NADP+/NADPH, are truly universal. If we're going to see evidence of multiple trees of life, it'd be in those little details because most of the food chain has to interact with each other. Or fungi and other decomposers can bridge the gap. I think over the span of billions of years, evolution tends to converge too much for the trees to remain very distinct from each other.
- anonymouskimmer 4y ago
  > There are a lot of microbes that are unculturable to this day Some of this has been solved by literally allowing the microbes to sit in culture for a year or so in order to either wake up from hibernation, or adapt to the culture composition. > see if the universal metabolic molecules like, for example, the hydrogen carriers NAD+/NADP+/NADPH, are truly universal. For anything that's based on DNA or RNA we now do direct sequencing of environmental samples. From this direct sequencing we can pull out individual genes and pathways. > I think over the span of billions of years, evolution tends to converge too much for the trees to remain very distinct from each other. We've got over 20 recognized genetic codes already from existing life. These are highly similar, but this probably points to similar origins instead of convergence.
__MatrixMan__ 4y ago
How many different biochemical schemes for life do you suppose the laws of physics support? It's probably a lot. But how many of those are successful enough that we're likely to have found their implementations? I'm thinking it's far fewer. Mostly just because "successful" is a hell of a filter, but also because the ability to eat your competitor is a hell of a benefit--which would create a bias towards compatibility and away from schemes that have to regard the users of competing schemes as unusable matter. This is supposing that certain parts of the periodic table are more hospitable to biochemistry than others (i.e. that we don't have transition-metal-based life forms that just operate too slowly for us to notice, or some other orthogonal sort of way to be alive).

by samus 4y ago

akiselev 4y ago

There are a lot of microbes that are unculturable to this day and to my knowledge, no one has really done a proper investigation to see if the universal metabolic molecules like, for example, the hydrogen carriers NAD+/NADP+/NADPH, are truly universal. If we're going to see evidence of multiple trees of life, it'd be in those little details because most of the food chain has to interact with each other. Or fungi and other decomposers can bridge the gap. I think over the span of billions of years, evolution tends to converge too much for the trees to remain very distinct from each other.

anonymouskimmer 4y ago
> There are a lot of microbes that are unculturable to this day Some of this has been solved by literally allowing the microbes to sit in culture for a year or so in order to either wake up from hibernation, or adapt to the culture composition. > see if the universal metabolic molecules like, for example, the hydrogen carriers NAD+/NADP+/NADPH, are truly universal. For anything that's based on DNA or RNA we now do direct sequencing of environmental samples. From this direct sequencing we can pull out individual genes and pathways. > I think over the span of billions of years, evolution tends to converge too much for the trees to remain very distinct from each other. We've got over 20 recognized genetic codes already from existing life. These are highly similar, but this probably points to similar origins instead of convergence.

__MatrixMan__ 4y ago

How many different biochemical schemes for life do you suppose the laws of physics support? It's probably a lot. But how many of those are successful enough that we're likely to have found their implementations? I'm thinking it's far fewer. Mostly just because "successful" is a hell of a filter, but also because the ability to eat your competitor is a hell of a benefit--which would create a bias towards compatibility and away from schemes that have to regard the users of competing schemes as unusable matter. This is supposing that certain parts of the periodic table are more hospitable to biochemistry than others (i.e. that we don't have transition-metal-based life forms that just operate too slowly for us to notice, or some other orthogonal sort of way to be alive).