31–40 of 85 posts
If they find cells lacking some organelle, it will be hard to say whether it was never acquired, or was later abandoned. One clue would be leftover genes from when it was there. Eukaryotes often find it hard to prune out excess DNA, vs. just turning it off.
DNA doesn’t help as much as you think with single celled organisms thanks to HGT. Bacteria, at least, share DNA and thus we can’t use it to determine a linear evolutionary sequence.
Earlier quoted context omitted.
This is Nick Lane's argument - that complex cell happend only once on Earth (no convergent evolution) via this symbiotic accident and hence it's highly improbable if not almost impossible. As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.
> that complex cell happend only once on Earth Well, it's quite possible that once it happens, it voids any chance of it happening again just because life filling that niche already exists. If so, it only happens once, and this says absolutely nothing about the odds of that first occurrence. > what happened once, happens all the time That's a fallacy people do all the time here when talking about exobiology. It's bas…
Earlier quoted context omitted.
This is Nick Lane's argument - that complex cell happend only once on Earth (no convergent evolution) via this symbiotic accident and hence it's highly improbable if not almost impossible. As usual, people always seem to foreget that in this universe, what happened once, happens all the time and we are not special.
We're all just speculating given that were stuck at sample size = 1 until we develop near light speed travel. I get the convergent evolution point, but so far the story is that 1) life arose very quickly 2) then proceeded to do very little for billions of years. If that's true, then it's bad news for the possibility of complex life being common.
This is understating the feats of unicelular life. Those tiny organisms essentially terraformed the whole planet in those billions of years, oxidizing nearly all the iron close to earth surface, burying most carbon and then pumping so much oxygen in the atmosphere that at a point it comprised 30% of Earth gaseous envelope by weight. I wouldn't call that very little. To come close we'll need at least to terraform Mars or Venus, to match the feats of our microbial forebears.
If we assume single celled life is common, and exists in either all star systems, or in all systems without a hot Jupiter close to the star; then given the length of time involved here before eukaryotes, can we estimate how many planets in the galaxy have eukaryotes? Or how long it will be before some do? Presumably increasing the length of time increases the probability of occurrence as would increasing the number o…
> can we estimate how many planets in the galaxy have eukaryotes? Not yet. In the history of life on Earth, this has happened once. Knowing what we know about cellular biology, it’s stupidly unlikely. Beyond our present theories’ ability to quantify. By the way, I think this is one of—if not the—great filters. It’s unlikely to happen, to not promptly get smote by its primordial planet’s tantrums and to get it so righ…
this was all when eukaryotes engulfed prokaryotes, but still, how does this mean unlikely? it seems imminently likely, since.. it happened a bunch of times.
seems to me like prokaryotes evolve a strategy of engulfing others for their resources, then one day engulf a prokaryote infected by a virus, which transfers DNA across, rinse and repeat.
how is this more of a filter than abiogenesis?
Earlier quoted context omitted.
DNA doesn’t help as much as you think with single celled organisms thanks to HGT. Bacteria, at least, share DNA and thus we can’t use it to determine a linear evolutionary sequence.
HGT?
Because biology isn’t complicated enough. :)
If they find cells lacking some organelle, it will be hard to say whether it was never acquired, or was later abandoned. One clue would be leftover genes from when it was there. Eukaryotes often find it hard to prune out excess DNA, vs. just turning it off.
A most famous example is red blood cells, which are emptied of most organelles to make space for hemoglobin.
If we assume single celled life is common, and exists in either all star systems, or in all systems without a hot Jupiter close to the star; then given the length of time involved here before eukaryotes, can we estimate how many planets in the galaxy have eukaryotes? Or how long it will be before some do? Presumably increasing the length of time increases the probability of occurrence as would increasing the number o…
That could well be an accidental fact. Maybe on some planets we have a gradient of cell complexity.
Also, we don't really know what even simpler kinds existed on earth but were lost, since bacteria, the "simple" kind, it's obviously too complex to have been the first ever life form.
How simple are Prokaryotic Cells really? Like "simple" enough that we understand all the intricate workings of it, or "simple" enough to be made from scratch?