We don’t like to cover news on Astronomy Cast, but sometimes there’s a news story that’s interesting, complicated, and rapidly unfolding – and it happens to cover an area that we haven’t talked much about. So today we thought we’d talk about the discovery of arsenic-based life, and exotic forms of life in general. Maybe we need to redefine our definition of life. Or maybe we just got introduced to some distant cousins.
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Episode 209 Show notes and transcript
Calling it “arsenic-based life” is a bit extreme,isn’t it? So extreme as to be totally wrong – or are we and our cousins phosphorus-based life?
In the to and fro of the last weeks, Wolfe-Simon et al now clearly states what is implied by their paper, that at most a minute amount of arsenic is taken up and used. As most biologists seem to have said from the beginning, “It is not an arsenic-based life form”.
Despite lacking controls for almost everything they do, the author’s still claim that this could have been incorporated in DNA as opposed to, say, the very obvious vesicles that the As+/P- bacteria displayed. Their critics thinks not, and now we have to wait for the release of the bacteria to the community.
Or maybe not, because some point out that this is so unlikely a proposal that most would not do it, possibly not even get the grants to check up on it among the worthy study objects that are out there:
“In my view, the blogosphere discussion and my reading of the paper leave me with the working hypothesis that the idea that GFAJ-1 substitutes As for P in biomolecules at any interesting frequency, while not fully disproven, is improbable enough that it is not worth the opportunity costs involved in doing additional experiments… for me, or most people I know. That calculation may be different for Wolfe-Simon et al, as their scientific reputations are more heavily invested in the answers.
I should also note that further research along these lines is unlikely to be funded by any study section I’ve ever served on.”
Maybe GFAJ will just sit there, displaying how “Give Felicia A Job” was a proper descriptor.
[Since the previous comment has been stuck in moderation over the weekend (?), I’ll republish without the two offending links:]
In the to and fro of the last weeks, Wolfe-Simon et al now clearly states what is implied by their paper, that at most a minute amount of arsenic is taken up and used. As most biologists seem to have said from the beginning, “It is not an arsenic-based life form“.
Despite lacking controls for almost everything they do, the author’s still claim that this could have been incorporated in DNA as opposed to, say, the very obvious vesicles that the As+/P- bacteria displayed. Their critics thinks not, and now we have to wait for the release of the bacteria to the community.
Or maybe not, because some point out that this is so unlikely a proposal that most would not do it, possibly not even get the grants to check up on it among the worthy study objects that are out there:
“In my view, the blogosphere discussion and my reading of the paper leave me with the working hypothesis that the idea that GFAJ-1 substitutes As for P in biomolecules at any interesting frequency, while not fully disproven, is improbable enough that it is not worth the opportunity costs involved in doing additional experiments… for me, or most people I know. That calculation may be different for Wolfe-Simon et al, as their scientific reputations are more heavily invested in the answers.
I should also note that further research along these lines is unlikely to be funded by any study section I’ve ever served on.”
Maybe GFAJ will just sit there, displaying how “Give Felicia A Job” was a proper descriptor.
There is no general accepted “definition of life”. The most useful looks at the life process of populations, in the same way that one can do a proper and robust definition of other processes such as gravitation:
Biologists like to define evolution as “a process that results in heritable changes in a population spread over many generations.” This excludes epigenetic effects (the direct fixation of such, that is), but includes all phylogenetically related organisms including viruses.
Such a robust and inclusive framing definition also happens to show how irrelevant the substrate is. (To the degree that one has to explicitly reject genetic algorithms and adaptive von Neumann probes with schemata, or conversely keep biochemical populations, if one is unhappy with “un-biological” populations.)
It also shows how irrelevant it is with insisting that the necessary genomic and metabolic processes are coexisting in the same subsystem at the same time. Spores and (philosophically popular) infertile individuals are still part of the population, still living, even if contributing to its evolution only by coevolutionary forces. (Being the environment of, or later becoming, respectively genomic and metabolic working individuals.)
As another illustrative example, Mimi viruses _impart_ necessary metabolic genes to bacteria which otherwise would be unable to assemble and propagate the virus. Having more genes than the bacteria they prey on, they are more hereditary complex, more hereditary adaptive, more “alive”.
Really, the NASA definition, including metabolism, is a quick and dirty method to find living _individuals_. It is only by studying a population of such for several generations one can conclude if they are robustly alive, and not (say) an unlikely unadaptive immortal.
It is if faced with immortal individuals one would have to redefine life. But as noted, that is unlikely to the extreme, almost by definition an evolving population competes successfully with static individuals (which likely had to evolve in the first place, btw).
Ooh, I goofed. Now I remember that Mimi-viruses prey on amoeba – so they aren’t more complex than their prey in sum. They are more complex than “than at least 30 cellular clades”. (But Mimi, and Mama, viruses do provide multiple necessary enzymes that amoebas lacks. They are awesome!)
Could organisms that reproduce by division, such as amoebas, be considered immortal?
In principle perhaps. (Though as for infertile individuals I don’t see how that is more than a philosophical view of individuals as evolutionary important, the population genome wouldn’t “see” such individually immortal cells.)
But it seems they found out that dividing cells like bacteria have a “waste bin” end where they prefer to put their damaged genes, likely as an adaptation to unavoidable damage. After ~ 200 cell divisions (IIRC) an ancestral bacteria dies of damage.
I assume the same goes for amoebas in case they don’t have the telomeres of us multicellulars. The better gene machinery of eukaryotes is mostly making up for larger genomes, and amoebas should also die after some hundreds of divisions at a guess.
[It seems amoebas do have some type of telomeres according to recent research I quickly googled up. But I dunno if it has the same shortening phenomena as our own.
The later is ultimately deciding number of cell divisions, usually at a rather smaller number than for bacteria I think. AFAIU it is thought to be an adaptation to cut down on rate of cancers, something that doesn’t affect a unicellular life form.]
Has anyone seen all the controversy this claim of “life with arsenic instead of phosphorous” has raised. See for example http://rrresearch.blogspot.com/2010/12/arsenic-associated-bacteria-nasas.html. I wouldn’t be surprised if the article (http://www.sciencemag.org/content/early/2010/12/01/science.1197258) was retracted. I think such an extraordinary claim requires better evidence.
these starving bacteria can substitute arsenic for phosphorus to survive, where conditions exist away from a living host. they have falsely been called “alien bacteria” on other blogs.
They can _maybe_ substitute, it is part of the controversy AFAIU.