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| Heterochiral Biospheres | |
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| Topic Started: Sep 8 2017, 09:14 PM (240 Views) | |
| bcforstadt | Sep 8 2017, 09:14 PM Post #1 |
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Zygote
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This might be against the rules, because technically nothing in this post is original, but I have questions about something that I would very much like to get a better understanding of, and I think it would be fruitful to put this in its own thread because it seems to be a very large and unexplored topic. Internet person "rekjenson" asks two similar questions on two different platforms: Heterochiral biosphere: a two-handed world and A two-handed world (heterochiral biosphere). The basic idea behind their questions: is it possible for a world to contain two distinct lineages of organisms of opposing amino-acid etc. chirality? I find this variation on the old shadow biosphere trope to be very appealing. There is a lot of room for exploration of things like symbiosis and mimicry. I am very interested in this stuff, but I'm also interested in the viability of the whole setup. I've divided up these worries into a few problems: The Extinction Question: Is there enough room on a planet, ecologically speaking, for two biochemically incompatible biospheres (Side question: is the terminology of biosphere even appropriate in this situation? I will assume for the rest of this post that it is) to exist without one driving the other to extinction? This question can be generalized to: The Development Question: Would the development of certain features in one biosphere "screen off" the development of those features in the other biosphere? For example, would the development of multicellular land autotrophs in one biosphere make it much less likely for "the other biosphere to develop multicellular land autotrophs? If so, interesting double biosphere worlds would be very unlikely - not only would the two biospheres have to miraculously fail to outcompete each other at the beginnings of life, they would also have to miraculously fail to outcompete each other at each stage of complexity, for there is an obvious (?!) implicational hierarchy (microbial life < multicellular land autotrophs < small "animals" < land megafauna / land sophonts) My final question: The Separation Question: Could the two chiral biospheres coexist without becoming one homogenous, racemic biosphere? In A two-handed world there is a discussion between rekjenson and blacksheep998 about this problem. Who is right? Basically, the problem is this: all the multicellular life in the world is developed from unicellular microbes that had enough time to develop ways of dealing effectively with both chiralities, so there probably wouldn't be any noticeable ecological barrier between the two lineages, so the multiple biospheres just end up collapsing into one. Panspermia might be a solution, but it's not really possible for complex life to hop between planets or moons without getting help from space aliens. I don't even know how possible for microbes that is. So ultimately, unless we're allowing space alien intervention, this looks like it kills the two-handed world proposal. Besides the question of viability, there are all sorts of other interesting areas to explore about these sorts of worlds. For example, habitats, and whether we might expect those of species of different biospheres to be separate from one another, or intertwined with one another. To what extent can we expect there to be "exclusion zones" between the two biospheres? Blacksheep998 brings up the fact that Earth fungi fling their spores into outer space to dispute the idea that exclusion zones could exist, but then again it's not like fungi *grow* in outer space, so if the two biospheres are sufficiently toxic to one another or hog resources from one another to0 much (???- a whole separate discussion!) there could be areas of virtual exclusion. In addition, double biosophere heterochiral worlds might disincentivize fungus-like reproductive strategies anyway. Immune systems on these sorts of worlds are also bound to be interesting. How toxic are alternate biochemistries to each other in general? What if they live in a double biosphere arrangement? This is obviously closely related to my Separation Question. |
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| Tartarus | Sep 9 2017, 06:31 PM Post #2 |
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Prime Specimen
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I see no reason why two different lineages of organisms with different amino acid chirality could not both exist on the same world. As for how they would or would not coexist in shared habitats on the world I am not quite sure. |
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| syzithryx | Sep 9 2017, 07:47 PM Post #3 |
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Newborn
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Amazing as this idea is, I suspect a heterochiral biosphere would either be impossible, or be indistinguishable from ours because most creatures can digest both chiralities. |
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7:50 PM Jul 10