As Mono Lake is of volcanic origin and formed around 760,000 years ago (per Wikipedia) I'd be astonished if the arsenophile(?) evolved there in that short a time span. Which leaves open the question of where it came from, and whether arsenic tolerance is present but dormant in other extremophiles.
Other points of note: never mind the cellular DNA integrating arsenate, the whole respiration cycle seems to be affected, presumably running on ATA rather than ATP. Which implies huge amounts of molecular booty in the shape of enzymes that are powered by a different reduction gradient (ATA-AMA rather than ATP-AMP).
Possible down to earth applications? Lest we forget, Pakistan has a monstrous problem with arsenic-contaminated wells ( http://www.irc.nl/page/16331 ) and a bacterial culture that thrives on arsenic could offer new approaches to arsenic sequestration. And that's just off the top of my head. (My biochemistry is, alas, too rusty to go much further without a refresher course. Hmm ...)
Do you have any basis for the claim the 760k years would not be enough time for such a feature to arise? After all, some surprisingly complicated things (http://en.wikipedia.org/wiki/Evolution_of_the_eye) are believed to have evolved (more than once) over shorter periods.
Number of years is mathematically irrelevant. Number of generations is mathematically relevant. Bacteria produce new generations prodigiously.
Consider: antibiotics were invented less than a century ago, and bacteria have already evolved a resistance to penicillin. That's probably more than humans have evolved for 100,000 years. 100 years is like five generations for humans, but billions of generations for a bacteria. 760,000 years? That's tons of time for bacteria. Especially since bacteria are pretty simple; more complicated life has a much harder time evolving.
Assuming bacteria reproduce once per day, a century would be ~30000 generations. Not billions. 760,000 years ~ 3e8 days, whether that is "tons of time" I can't comment.
I just wanted to reiterate my suggestion for any bio-geeks living in the Bay Area - Mono Lake is only 2hrs drive from Bay Area and it is FASCINATING.
I would really encourage anyone who is interested in ecology and biochemistry to go check it out if you are passing through to Mammouth Lakes for snowboarding or taking a trip to Yosemite which is next door.
Arsenic is this big: (makes gesture with thumb and forefinger a few angstroms apart), bacteria are this big: (makes gesture with thumb and forefinger a few microns apart).
OK, that's not overly helpful, the point being, you can filter bacteria out of water a whole hell of a lot easier than you can filter out dissolved arsenic.
1) precipitating arsenic salts directly might be easier and a whole hell of a lot easier to provably run to completion.
2) to filter out bacteria, you'd have to grow bacteria. In addition to arsenic, you'd also have to add sugar and protein. Last I checked, Islam take a pretty hard line on beer.
However, beer is made with yeast, not bacteria. And from what I can tell, most reasonable forms of Islam interpret the beer thing as forbidding intoxication. I don't think any forbid bread (solid beer), for instance. Yogurt and pickles are also made with bacterial processes and I don't think they're forbidden in Islam.
Clearly, the bacteria aren't going to magically destroy the arsenic. But eat the arsenic, die and float to the surface of the well where they can be skimmed off? I'd say that's a simple goal for some genetic engineers to start gunning for.
It's also plausible they could metabolize it into some non-toxic form. (We've got a variety of biomolecules we've never seen before, some of which could be non-toxic.)
Possibly a small sludge pond that would filter the water through as per a sewage treatment plant?
I'm thinking that if it's in the wells, it's due to the solvent action of water on the rocks, and cleaning out the wells would only be a temporary solution.
Currently AIUI they use ion exchange resins as filters. Which is okay, but they run out eventually. A sludge pond might well be a better solution (although that's best left to an environmental engineer -- do we have any on HN)?
BTW, the ATP-AMP reaction is not a electrochemical reduction reaction, it's rather the mundane hydrolysis of a phosphodiester bond. We don't know what the energy potential of an arsenodiester bond is (although some speculation is that it carries a bit less energy).
I'd use the word arsenotolerant instead. The cells still preferentially utilize phosphorous when given the option. The prefix phile generally implies that they require such conditions to live, like a thermophile isn't viable at a temperature below (roughly) 40 C. This organism would have no trouble growing in the absence of Arsenic. =)
OK, this news is very interesting, but it does not prove much about extraterrestrial life.
We know that organisms can adapt to their environment. Incorporating some fraction of arsenic into a cell's dna is an example of such adaptation.
The question that really matters is "has life originated more than once in the universe?" This experiment has no bearing on that: They took a standard terrestrial cell, with a carbon-based history, and simply subjected it to some new conditions. This is NOT a new life form that originated from a novel environment and using a different chemistry. However, NASA is getting awfully close to selling it as such in their press conference, which is misleading.
if you're watching the press conference, they're very adamant that it doesn't prove anything about extraterrestrial life and they aren't able to yet say if life evolved with the arsenic or if it adapted.
but they're pointing out that it does show that forms of life different from our current definitions can exist and therefore the possibility of extraterrestrial life in non-earthlike environments exist.
"but they're pointing out that it does show that forms of life different from our current definitions can exist"
Yes, but not meaningfully different from previous definitions. If this is simply an evolution of existing earth life, then it's just another in a long list of things that we were surprised evolved from conventional Earth life, but is, nevertheless, conventional Earth life. It's more indicative of a slight flaw in our definitions, not time for a radical reexamination of our assessment of the universe.
As I commented in a previous message, people have a history of getting far more excited about this sort of thing than they have scientific justification for. This sure looks like another one of those.
Now, if they could establish that this has to be the actual entirely new branch of life that can be provably not traced back to the same Earth ancestor as everything else, that would be a groundshaking discovery.
Those of us pondering the Great Questions were already not assuming that everything has to look exactly like known Earth life to work. There are numerous obvious different, incompatible mechanism that could exist (different RNA transcription tables, the other chirality for proteins) and an unknown and presumably vastly larger number of unobvious different mechanisms even just for basically Earth life before we really go out into new territory. We've already speculated endlessly about silicon life, ammonia life, mechanisms other than photosynthesis, etc. Don't get me wrong, this is legitimately interesting, and would on its own be worthy of HN, but I have to say the implications for the Great Questions are basically zip. Announcing proof that life can only exist in precisely Earthlike conditions with incredibly tight tolerances would be the surprise.
i think that it is meaningfully different from previous definitions.
perhaps all sparks of life would require the same stuff that it did on earth, that is unclear. but it shows that the continuation of life doesn't necessarily require that same stuff. it means that in searching for life, you don't necessarily have to limit it to the proverbial class M planets.
But how is that a change? We already knew that to the point that we're looking at non-Earthlike planets. We're already looking for life on Titan and Europa, already looking on Mars to see if it had life. We're already talking about life on that tidally-locked mega-Earth that came up a couple of months ago, with otherwise-respectable scientists saying it's 100% likely [1]. We're already not convinced that life has to start exactly as Earth does.
If it's "different", what's the actual difference? What actually changed?
no. we already theorized that, we didn't know. we didn't have proof. now we do; now we know. the actual tangible differences are likely going to be in funding, research direction, and scope of effort on the topic. who knows what future research will generate off of this?
no, the world hasn't changed. sorry. not yet, at least. but its kind of like watching the moon landing in '69 and scoffing at it because you knew it was coming, you've been reading about NASA working on it for years in the paper.
You're badly misunderstanding my point. I'm not saying this isn't interesting. I'm saying this isn't actually all that interesting when it comes to the Great Questions. It doesn't significantly expand where we already thought life could be. It has not yet established that it is anything other than another evolution of Earth life, which would be a big deal, and from the sounds of it that's still what it is, an adaptation.
This isn't some amazing announcement with profoundly unsettling implications for life in the Universe. It's another in a long series of announcements about how our understanding was limited about how far Earth life could travel. It's roughly similar to how we found non-photosynthetic life around the ocean vents [1], or the recent discoveries of strange life several miles underground [2], or the sky bacteria [3]. I think quite a few people here are not understanding just how many similar discoveries have already been made, we moved on from "all life in the universe will look just like the standard sun-powered ecosystem we live in" quite a while ago.
I guess you could say to the extent this is amazing, we've already been amazed this way. It's cool, but it's a discovery that fits quite comfortably with a number of other interesting discoveries. We're not going to be talking about this in another year. (Except possibly because once people start looking for more examples of this sort of thing I'd lay money they find them.)
Well, no. To know that we'd have to find it to act as proof. What this finding does is expand the bounds of the environments in which searching for life is viable. In other words, we can now consider other temperature ranges and chemical soups and compare them against a new baseline for viability.
I agree that this is remarkable, but I think it's valid to criticize publicizing the finding as an astrobiology discovery, which is exactly what NASA (or its public relations department, at any rate) is calling it--and which it is not, despite its implications for astrobiology.
If we care about engaging the public, we should be concerned about sensationalism that detracts from the solid work of the scientists. If you cause people to think you're going to show them extraterrestrial life, fairly or not, you run the risk of them tuning out when the reality is less flashy, even if it's groundbreaking.
I'm surprised by the strong objection. I understand that the lead scientist is with the NASA Astrobiology Institute, but I still think that despite the important implications for astrobiology, calling it astrobiology is questionable. If neither NASA nor any astrobiologists had been involved, exactly the same results could have been obtained, and the astrobiology connection (though it might be played up because it is an interesting angle) would more clearly be incidental. In other words, I don't think you lose any accuracy or diminish the finding by referring to it as biological rather than astrobiological.
That said, I'm not sure I really want to get caught up on "biology" versus "astrobiology" as terms. I think the greater point (or at least the point I was trying to make) is about communicating clearly and managing expectations. When you say astrobiology or exobiology, invariably some people are going to cry, "What, no aliens? You tricked me!" If that indignance prevents them from trying to understand the importance of the story, should we even bother trying to cater to them? I don't have a good answer for that. Without raising the idea of extraterrestrial life, they might not have been engaged at all. It's just something for those involved in public outreach to be aware of.
I guess I tend towards thinking of astrobiology as the subset of biology dealing with life beyond Earth--a convenient and arbitrary definition, perhaps. In any case, under this definition, with no validated extraterrestrial life, astrobiology would be a largely theoretical science or a line of philosophical inquiry. But if that's too narrow an interpretation, maybe this indeed is an example of experimental astrobiology. Hence, I may have overstated my position when I said this is not astrobiology.
At this point, however, I fear I'm drawn towards philosophical digression. It seems the motivation of the scientist comes into play because she could end up with the same results whether she is a) looking for insight into how life could exist elsewhere in the universe or b) studying life in extreme conditions on Earth. The impetus and interpretation become the categorizers (in practice, I don't think it's too cynical to link this to funding source). On the broader question, I should perhaps defer to the epistemologists--does the nature of knowledge change depending on why it was sought or what is made of it?
Back to the question, what would I consider astrobiology? Well, if life or its precursors were found on Mars or a comet, that might work for me. But what happens when it falls to Earth? I don't know; I've never been particularly comfortable with the blurry divisions between disciplines anyway, so if I consider the dividing line between, for example, psychology and sociology to be tenuous, how am I supposed to feel in this instance? The thing is, knowing what to call it doesn't really affect our ability to understand or use it, it just changes the way we talk about it--which may be important, I grant. But this brings me back to the communication aspect. And as far as that goes, I feel like I've gone through a lot of words without saying much. Therefore, let me summarize like so: I understand why they call this astrobiology; I probably wouldn't call it that myself; most importantly, I think many people will be expecting something else.
So, exactly where in the paper did they show that there was DNA that had an arsenic backbone? They just showed that there was arsenic in the sample that they think is DNA, and not very much phosphorus. That could be contaminants. But also, how do they know that sample is the "DNA sample"?
That's fair, they didn't prove an "arsenic backbone," but here's a couple of key lines...
"...the purified DNA extracted from +As/-P cells contained As. Our NanoSIMS analyses, combined with the evidence for intracellular arsenic by ICP-MS and our radiolabeled AsO4-
experiments demonstrated that intracellular AsO4 was incorporated into key biomolecules, specifically DNA."
and
"...the level of PO4 impurities in the medium was insufficient to elicit growth in the control (-As/-P)"
I agree. Note that the cells are not phosphorus-free. The paper states that the cells grown without phosphorus contained 0.02% phosphorus, presumably due to impurities in the reagents. Based on the numbers in the paper, it seems like this is enough phosphorus for one copy of the DNA genome.
My hunch is that the bacteria are able to use this low level of phosphorus, rather than replacing phosphorus with arsenic wholesale. It seems unlikely to me that the bacteria have evolved to use arsenic in place of phosphorus in the DNA, in ATP, in phospholipids, and in everything else. It seems even more unlikely that they can dynamically switch between arsenic and phosphorus for all their purposes, since all the enzymes would need to work with two different substrates. (In other words, changing an enzyme to work with As instead of P seems hard; changing an enzyme to work with As or P as needed seems much harder.)
That said, I think this is a cool discovery, and it will be interesting to see just how much of the biochemistry is actually using arsenic, since it seems that at least some is.
..based on their MS measurements. They can't accurately calculate for impurities that might be in the source medium, there's no negative control on that.
Huh! Biochemistry major here... So I guess that the bacteria just rarely uses Sulphur-Sulphur (thiol) bonds in it's proteins, since Arsenic has a high affinity for it (and that's what causes arsenic toxicity in everything else).
http://en.wikipedia.org/wiki/Arsenic#Biochemical_basis_of_ar...
"suggesting the possibility of a biochemistry very different from the one we know"
Seems like a bit of an exaggeration, but news will be news. Thiols are important for the structure & enzymatic activity, but this bacteria is proof that there are ways around it. Besides that difference, I'm guessing they're the same.
it's a really big deal... provided the arsenic is actually incorporated into nucleic acids, and the bacteria aren't just surviving on background levels of phosphate.
it will be interesting to read the original paper when it comes out in Science later today, and not just accounts of the paper from other sources
Yes, beside the fact that they found a way to change the structure of their DNA, RNA, and a few hundreds enzymes involved in energy metabolism they are the same...
This is so huge that my money go into a mistake: I bet these bacteria just found a way to either get rid of arsenic or to neutralize its allosteric toxicity by maskerading or something. The paper is not out yet so I cannot give my opinon on the experimental data but from what I read there is no evidence that DNA actually contains arsenic and until that arrives I believe it's a red herring.
"from what I read there is no evidence that DNA actually contains arsenic"
FTFA: "When the researchers added radio-labelled arsenate to the solution to track its distribution, they found that arsenic was present in the bacterium's proteins, lipids and metabolites such as ATP and glucose, as well as in the nucleic acids that made up its DNA and RNA. The amounts of arsenate detected were similar to those expected of phosphate in normal cell biochemistry, suggesting that the compound was being used in the same way by the cell.
The team used two different mass-spectrometry techniques to confirm that the bacterium's DNA contained arsenic... Analysis with laser-like X-rays from a synchrotron particle accelerator indicated that this arsenic took the form of arsenate, and made bonds with carbon and oxygen in much the same way as phosphate."
The author themselves are tyring to explain to you that "Our data are strongly suggestive of arsenic replacing phosphorus". Where suggestive =!= evidence.
Plus, read the paragraph "A world of possibilities" to see why so(FTFA).
There is no evidence. There are results that are compatible with that and other scenarios. Science is not so easy as you wish it was.
If you want absolute proof without any possibility of doubt go to church. If you want a series of ever more robust hypotheses supported by growing evidence which "suggest" possibilities, then you want science.
This is the first result. It's not foolproof but it's very, very suggestive.
Maybe I misread the article but I thought that the bacteria did not multiply if there was neither phosphorous nor arsenic present, but did multiply if there was arsenic but no phosphorous. I could be interpreting this wrong but this seems to rule out "neutralizing" or "getting rid of" the arsenic. (Otherwise why was it unable to multiply in the absence of phosphorous and arsenic?)
Bacteria multiply just fine (in fact better) with phosphorous but seem to cope with arsenic too. This is in my view a strong indicator of a mistake or flaw in the paper because it'd mean that if the authors' speculations were real, those bacteria would have evolved thus to modify a great deal of their biology just little enough to be able to incorporate both arsenate and phosphorus. It doesn't make sense.
<a href="http://dl.dropbox.com/u/52420/Science-2010-Wolfe-Simon-scien... the PDF</a> of the paper, btw (I don't like scribd).
I'm sure DNA physical structure (angles, bends, etc.) with Arsenic instead of Phosphorous won't be exactly same. Arsenic has same tetrahedral structure as Phosphorous but the atom is sure bigger in size and at DNA scales, size would play a large role in determining shape of molecule. I'm sure you realize that physical interactions play a great role in a cell.
It's true that the subtle loss of a hydroxyl group leads to all sorts of differences between RNA and DNA (RNA likes to be single-stranded more than DNA does) but there's TNAs (unfortunate acronyms) and PNAs (not to be confused with PNAS) and other things that basically work and look like DNA with fairly un-subtle changes.
Furthermore, Arsenic really isn't THAT much bigger than Phosphorus (vdw radius 1.85 vs 1.80; covalent radius 1.19 vs 1.06).
high resolution Mass spec is such a shitty technique and is completely non-quantitative. How do you know that arsenic isn't associated with, say, a protein that makes the DNA resistant to being taken apart chemically. I will believe this result when they stain the DNA and run samples of the DNA down a density gradient ultracentrifugation and show that arsenic content in the media correlates with increased density of DNA, as you would expect if the arsenic is replacing phosphorus. If you don't know what i'm talking about, it's this classical experiment:
Here is my personal scientific experience speaking: If you see it everywhere, then it's likely to be an artefact. Clean up your technique, clean your instruments, and go back to an old school technique. Remember how the physicists who discovered CMB cleaned out the pigeon scat from their microwave horn telescope before they started to believe what they saw.
"The researchers isolated the organism and found that when cultured in arsenate solution it grew 60% as fast as it did in phosphate solution — not as well, but still robustly. The culture did not grow at all when deprived of both arsenate and phosphate."
I had the same impression. This sounds really, really cool but it's still an organism that uses DNA, and we're still related to it. As a layperson, I don't see why this says a lot more about the potential for life elsewhere. If it's not a wholly new occurrence of life, then it's something that "did life" the same way we do until it happened to need this really cool adaptation.
I understand that my lack of biology training probably contributes to my not getting it, but that's where most people are coming from. A lot of time has been spent explaining the significance of Einstein's work and most people still don't "get it", we may need the same here.
So, instead of snarking...explain again/better/differently than others have.
We don't know of any form of life that isn't related to us at all. We have no strong evidence that such life has ever existed (although we have reasons to believe that it could have, before DNA-based life ate it all). For such life to exist on Earth today, it would have to compete with our relatives, and that's hard to do now, as it has been for billions of years.
So if nothing short of finding a completely unrelated living organism is going to excite you, the odds are strongly in favor of your being bored with biochemistry for as long as you live. Better change the channel.
All I know about biochem is what I learned by listening to Lander and Weinberg on MIT OpenCourseWare, but even I know that (a) every lifeform on earth has phosphorous-based chemicals at the center of its metabolic mechanism; (b) every lifeform on earth uses phosphate-based chemistry -- DNA or RNA, specifically -- as its genetic mechanism. These are the things you learn in the freshman class. Evidence that there might be an organism alive right now that violates one or both of these rules, even partially, is very exciting.
With our luck, they made some kind of mistake, and we can all go back to the status quo once they find the error, get totally drunk, and then issue an apology. But, if not, whole careers in biochemistry will be spent studying this.
> This sounds really, really cool but it's still an organism that uses DNA
Are we 100% certain of that? I'm not a biologist, however it seems to me that DNA is in part defined by the usage of Phosphorus. Maybe we need to redefine DNA? Or does this organism not use DNA at all?
Yeah, I don't know either. Sounds like DNA is the strand/mechanism and using phosphates is all we know of so far. IANAS
But if it's not-technically-DNA-anymore because it can use an arsenate instead of a phosphate, it's still part of our tree of life. That's the part that seems to have dampened enthusiasm somewhat.
I think it's more that this isn't very game-changing. Einstein revolutionized physics with relativity; Darwin revolutionized biology. What does this discovery revolutionize? Biochemistry perhaps, but it seems a bit too specific to have far-reaching impacts.
Tee-hee - it's true that these NASA announcements are often a bit of an anticlimax, but I suppose that's the price of having so much science-fiction to enjoy.
Oddly enough,the first bicycles were actually made out of wood - they were called velocipedes and today we call them balance bikes. Like scooters, they were powered by pushing feet along the ground. I was going to link to an amusing site about these, but while looking it up I was surprised to discover that there are in fact modern bicycles mostly made from wood, although they're quite expensive: http://www.renovobikes.com/
...so I wasn't as well well-informed as I thought I was.
I don't know. You would think, but you can autoclave a solution of "deionized ultrafiltered water" which should have "no" carbon in it at all, and bacteria will find a way to grow in it if you get it contaminated, they will concentrate the trace trace trace amounts of carbon.
How carefully did they prep their DNA? These days nobody is careful and they use these crap kits which are good enough, convenient enough to get molecular biology done. The other day in lab I suggested someone isolate DNA using caesium chloride gradient ultracentifugation and the only people who knew what I was talking about were the two old (70+) year old senior scientists but they agreed that it was the way to go.
The lead author gives a talk at 2:26 in Part 1 that I thought was an excellent example of how to communicate science (or other technical subject) and implications to a general audience.
Perhaps NASA should be more cautious about holding a press on astrobiology, and with a Science embargo. Clearly everyone will immediately think of aliens, and for good reason. It's NASA, it's about astrobiology, and it's something big enough to embargo Science. They're just asking for all the alien stories. And let's be clear, these are not aliens.
Holding a press conference for this pretty sweet discovery was completely justified. The language in the press release made it clear ahead of time that Nasa didn’t make any discovery related to life on other worlds, only a few overly eager bloggers spun crazy theories like that.
Whoever is disappointed by this and claims that Nasa hyped too much doesn’t have her or his head screwed on right.
I agree that it's an amazing discovery. Admittedly I didn't read the actual press release so you're probably right that they acted correctly. I only read second hand accounts of what they were going to announce.
We not only could have a common ancestor, it seems to me to be almost certain. What are the chances that some other life has evolved with DNA completely independently
Well, DNA is fairly complex. Of all the elements and compounds life could involve it seems rather unlikely that DNA evolved in two places completely separately. Not impossible, but very unlikely.
actually, no. DNA/RNA are in fact, just about the simplest chemical choices that can perform replication. Ribose, for example is the lowest energy pentafuranose, which means in a random mix of sugars you'll find ribose in the highest concentration. The funny thing is that the KSS principle seems to hold in nature, we've tried in the lab to design alternatives to DNA/RNA, and none of them seem to work quite so well.
This seems silly. Phosphorous not being required for life seems obvious to me: ok, maybe it's believed to be used in all Earth-originated, carbon-based life, but why would we believe a priori that it's an absolutely necessary component of any biological life anywhere (which seems to be what's implied by NASA and the relation of this to exobiology)? If we develop silicon-based artificial intelligence (how do you define life, anyway? That matters when you're talking about astrobiology), would we run a headline, "Researchers prove carbon not required for life"?
I've always thought the scientific community stated that alien life may use a totally different biochemistry from us?
Edit: so, in some senses this is like P!=NP being proven, except less important, since it's only one component (phosphorus). It's scientifically a big deal but doesn't change the world because it's largely what we've always expected (the metaphor breaks down that this doesn't have the major secondary consequences like N=NP would).
> Phosphorous not being required for life seems obvious to me
It hasn't been noticed or proved, and conclusions drawn from actual science have a tendency to disprove common sense once in a while, which makes any actual discovery worthwhile.
I don't think this is hindsight bias though. As a scientist (not in biochemistry or astrobiology, though) I understand this had to be specifically shown, but this is one of those things that most people I talk to and I have always just casually treated as obvious. The confirmation is important scientifically, but shouldn't change our viewpoint, since it's what we've always expected. Am I wrong here? Any computational biologists or biochemists want to tell me this wasn't expected at all?
You can argue that possibility of alien life is also quite a common idea. Yet a confirmation of that would be considered a major scientific breakthrough.
Yes, I agree here. Slightly stronger because though the possibility of alien life is entertained, it's not necessarily the common viewpoint that its widespread and will eventually be found in droves (like I see non-carbon based life). On the other hand, I expect fully us to be looking back several hundred years from now wondering how we could have ever thought we were the along lifeform in the universe. But a major scientific accomplishment it will be when it's first discovered, for sure.
Suppose Monopoles were discovered. Nothing really rules out their existence, Gauss's Law for magnetism is just an assertion that we've never seen a monopole, it's possible to patch up maxwell's equations to get monopoles. To some people, the existence of monopoles is 'obvious'.
It would still be a very big deal if monopoles were to be discovered, even in trace amounts, and no feasible way to make more of them.
Speaking without any domain knowledge, I think it has to do with "what can support the complexity required for life?". I would think it requires molecules that can do interesting things while at the same time survive their environment long enough to do those things.
It has to do with electronegativity and number of free electrons. Both phosphorous and arsenic can make three bonds, and arsenic is only very slightly less electronegative than phosphorous.
I thought free electrons might have something to do with it, but I'm making do with an only slightly better than high school education in chemistry here.
I think the first artificial, human directed production of antimatter was by CERN in 1995. I'm not sure what you mean by "two weeks ago", but antimatter has been around a lot longer than that.
Two weeks ago, CERN made the announcement that they had contained antimatter long enough (at LHC) to study it properly. First time it's ever been done that well. Pretty stunning accomplishment.
Why people constantly stick to the idea that all possible organisms must have similar biochemistry to us is beyond me.
Think about it: Out of the humongous search space of chemicals, the ones we use happened to work for us. A combination of randomness and building on what worked before got us to where we are. Why should life not be able to use chemistry in completely different ways in order to replicate itself? Why are we so arrogant as to think that our design is the only design?
Edit: My point is that our ratio of "shit we know" to "shit we don't know we don't know" is infinitesimally small in the field of possible lifeforms' biochemistry. That is, we only know stuff very close to us on a cosmic scale; we effectively have blinders to all other possibilities. And there's already a lot of biochemical variation on Earth: To give some small examples, viruses don't even have DNA, and plants use less amino acids than animals.
The self-similarity of what we have so far can be explained, I think, by evolution. We all started out from the same point, so there's very little incentive to "reinvent the wheel" as it were. Only under extreme conditions like we have here, or the geothermal vents underwater, do we observe marked differences.
> Why are we so arrogant as to think that our design is the only design?
We're not. Nobody is. The reason scientists don't look for life on other planets that is made of other chemicals is that we may not be able to recognize that as life. It's much better - read, scientific - to look for something we can recognize.
Also, there are chemical properties of the elements that make up life on Earth that allow for fast reactions, bonding, etc. Most of the rest of the elements in the periodic table react more slowly in normal conditions, making the process for life less likely. Not impossible. Just less likely. We think.
So we focus on looking for what we know about. That's the best way to do it. Nobody worth their degree will ever claim that our "design" (bad word choice, by the way) is the only one.
I wasn't trying to address any bearing this has on finding alien life, just speaking theoretically - we shouldn't assume that everything should be like us. If it hasn't been your experience that most people think that way, then I must have misjudged.
I agree on the second paragraph, but especially the last sentence.
I know "design" is used by IDers, but what other word can adequately reference the incredibly complicated way our cells and bodies work?
Use "structure", not "design". As in: "The human body's structure is...", not "The human body's design is...".
There is no need to use the word "design" to refer to the complexity of the human body. "Design" implies a creator; "structure" simply describes those aspects of the human body (or life in general) that makes it "work" and does not imply a creator.
I agree with you that other life structures seem quite possible. I don't see the problem. But I'm not a professional biologists.
Still, it seems there are a number of biochemists who believe (or believed) that the structure of earth life could be unique. These people knew a lot more than me. So I wouldn't credit this to arrogance so much as a very complex question, one that doesn't necessarily get easier to solve the most data you get (at least on our scale of data).
I don't think it explictly comes down to such hubris. Certainly there are a lot of biases in this subject just like there are in any other ("rap isn't music," for instance), and human history is rife with analyzing the world in terms of the analyzer's perspective, the very definition of bias.
While replacing nitrogen in the air with, oh, sulfur, would likely have resulted in life forms (so the story goes) with an entirely different chain of evolutionary reactions and mutations, resulting in different body chemistry, yadda yadda yadda.
I do think it's news when we find out what one of these parallel evolutions might consist of. I mean, I'm not even sure sulfur-air would be a gas, so it's one thing to guess and speculate (fun), it's quite another to be able to say, in scientific fashion, "OK, what else is possible on this arsenic branch?" Said another way: there are a lot of grant proposals being written right now to finance exploration of this new territory. Hey, it beats paying for research into animals who produce petrochemicals as blood.
Who are people in this case? Most people don’t at all know what kind of life is plausible and not and they don’t care. I’m certain, however, that many biologists had an opinion on this prior to the discovery and I’m not really sure whether they thought that it was unlikely. For all we know most biologists expected this or a similar discovery, they just couldn’t yet assume it to be true because there wasn’t any evidence. Until now.
I think you might have confused unwillingness to talk about things we don't know with unwillingness to admit the possibility of things we don't know. Having some knowledge in common helps make conversations interesting. When two people talk about a possibility that's in the head of one of the participants, the conversation is unlikely to be on equal footing.
Don't mean to get all religious on ya, but I wanted to ask here...
Is there any evidence of macro-evolution having ever taken place in recorded history? I'm asking this with no agenda, but curious. As far as I know, no new species have ever been produced, despite natural or unnatural selection.
So what makes us say that there is no other force or process that causes speciation? How are scientists so convinced that mutation and natural selection is all that is required, despite never having observed a single instance of speciation?
To be scientific, a theory has to make some potentially falsifiable, non-obvious predictions. Then we can test those predictions, and if our experiments confirm them then the theory survives. I totally agree that the hypothesis "natural selection occurs" has been proven in ample ways (ok, maybe the white->dark->white butterflies was a bad one, but bacteria and their resistance to antibiotics is proof enough). But to form a completely new species...
Species is defined as "as a group of organisms capable of interbreeding and producing fertile offspring" according to Wikipedia. Two animals are of different species if none of their offspring have ever been observed to be fertile. At least, that's a good working definition.
It bothers me that scientists have been interbreeding literally thousands of generations of fruit flies and despite all selection pressures, artificial or not, were never able to produce a single new species. Sure, it's hard to try and mate every fruit fly with every other fruit fly, so maybe there were divergent species, but after a few generations, this should have revealed itself. If this is really the case, then how come we take it for granted that humans, homo erectus, neanderthals etc. were all divergent species that had a common ancestor something like 50,000 years ago? Am I way off? If you take the fruit fly lifetimes and human lifetimes, in those 50,000 years we had about as many generations as the fruit fly generations. And we got all this speciation supposedly, using nothing more than mutation and natural selection. But where is the proof?
I'm not necessary arguing that one of the religions is right and there is another force. But are scientists being biased here when they simply assume there isn't any other force? It's as if I was looking at cars from the 1920s all the way up until now, and I saw gradual change, and based on this I decided that there was no designer of these cars. I don't think that follows at all.
Just curious if someone knows links that can resolve this for me :)
It's supposedly an industrial secret, but hearsay is that Abbott laboratories took the strain of bacteria that makes erythromycin and began serial UV-mutagenesis it to improve titers. It went from trace production to making 10-50 grams of drug per liter of media, which is quite amazing. As a result the bacteria has reconfigured its entire metabolism. Started out as a sessile, filamentous bacteria with a highly complex life cycle and now is a roughly spherical free-floating bacteria.
"Species is defined as "as a group of organisms capable of interbreeding and producing fertile offspring" according to Wikipedia. Two animals are of different species if none of their offspring have ever been observed to be fertile. At least, that's a good working definition."
Just so you know: That is just about the worst definition for microbiologist. Bacteria don't grow by sexual reproduction, they reproduce by binary fission. They also share genes like crazy. I've seen a gene taken from a sargasso sea sample crop up in the database for a bacterium found in the deeps of the medeterranean ocean. There is speculation that a virus is responsible for spreading photosynthesis between several different, otherwise very distantly-related clades of bacteria.
I fully agree that bacteria, rotifers, and other creatures can pick up genes. This is incredible. In fact, they've just found bacteria that substitute entire elements, which is incredible too.
What I am asking about, is the specific hypothesis:
"all speciation occurred via repeated application of mutation and natural selection, and no other factors were involved"
Now, I realize this would be impossible to test for ALL species, but wouldn't it be nice to have an example of at least ONE species that arose in this way through sexual reproduction? We have been breeding dogs for hundreds and thousands of years, and all of them are the same species! We have been adapting plants and never been able to create new species. Why is it so hard to do it, or it's just that we haven't tried hard enough?
I'm basically taking a skeptical approach here to the hypothesis, you see what I mean? It would be nice to just call it all "evolution" and assume the results. But I'd like some proof, some falsifiable predictions that have been tested.
well you better be willing to wait. Coli double every thirty minutes. The LTEE experiment took ten years. Find an organism that can sexually reproduce every thirty hours, and your equivalent experiment would take six hundred years.
With no description I almost didn't click on this link, but I'm glad that I did. The title of the paper it links to is "29+ Evidences for Macroevolution, The Scientific Case for Common Descent" and is worth a look.
Yes, I have seen talkorigins before and I use this all the time when people ask "how do you prove macroevolution"?
Certainly I can prove that macroevolution has taken place, if by that you mean that natural selection and mutation take place, and that the change is gradual, and topologically continuous.
"A unique, historical phylogenic tree" -- this pretty much expresses that idea.
But where in that paper does it talk about actual testable predictions of the hypothesis: "all speciation came about as a result of mutation and natural selection with no other factors or forces"?
Each section has a "predictions" section. But notice that even if all these predictions come true 100% of the time, this does not rule out the possibility that new species of sexually reproducing organisms are created specially by God, much like new cars are created by humans, despite there being an observably continuous change through time.
Look at this. We are almost there, to what I am looking for. Are these "speciation events" fitting the "mating preference" criteria or "cannot produce fertile offspring" criteria? If the latter, I am satisfied!
But notice that even if all these predictions come true 100% of the time, this does not rule out the possibility that new species of sexually reproducing organisms are created specially by God, much like new cars are created by humans, despite there being an observably continuous change through time.
That's just how the scientific method works. If you're looking for certainty, this isn't where you'll find it. Science can only tell us what we think is most likely to be true based on what we can observe.
It depends exactly how strictly you define speciation. If you follow the 'weak' version of 'these two populations will not normally breed with each other and create viable offspring' then we've done it a few times with flies [1]. We've created populations that will not normally breed with each other.
If you pick a stronger version, where they -cannot- breed, even if you were to preform in vitro or something similar on them, then we haven't quite done that yet.
I just looked at that section. They present three examples:
flies - but they say only a "mating preference" was achieved. Well sure, there are different kinds of dogs and they probably prefer their own kind, but they are still just one species.
domestic cattle - this is a non-example, as the article points out, because they are all capable of interbreeding
sheep - two kinds of sheep are apparently different species. However, I would take issue with this statement: "For example, domestic sheep were created by hybridisation"... it seems inconsistent with the other one: "but the initial dates and methods of the initiation of such species are not clear". How do they know they were created by hybridisation?
"How are scientists so convinced that mutation and natural selection is all that is required"
They believe no such thing. Selection isn't required for allopatric speciation. Two isolated populations will naturally start to diverge just due to drift (random genetic changes over time). Given enough time they will inevitably become sexually incompatible.
"As far as I know, no new species have ever been produced, despite natural or unnatural selection."
"We begin with two distinct, but related species. The pollen of one is painted on the stigma of the other. If a hybrid offspring is generated, it is usually sterile ... However ... the chemical colchicine can often restore hybrid fertility. It does so by causing the hybrid to double its number of chromosomes ... Hybrids so produced may be interfertile with other hybrids like themselves, but not with the parental species. They are then a new reproductive species."
"Most garden varieties of irises, tulips, and dahlias, for example, are artificially created species. But their numbers are dwarfed by the huge numbers of artificial hybrid species of orchids, which it has been estimated are being formed at the rate of about 300 per month."
"Polyploid hybridization is also important in natural plant evolution."
Now, that type of speciation is a special case. It is not how animals speciate. But you are quite wrong in your quoted statement above.
"how come we take it for granted that humans, homo erectus, neanderthals etc. were all divergent species that had a common ancestor something like 50,000 years ago? Am I way off?"
Yes, you are, by an order of magnitude. Homo neanderthalensis is supposed to have diverged 500,000 - 800,000 years ago. http://dx.doi.org/10.1126/science.316.5827.967a ("The new findings also push back the date that Neandertals split from the human branch of the primate tree by 200,000 years—to 800,000 years ago")
"maybe the white->dark->white butterflies was a bad one"
Don't believe everything you read in AnswersInGenesis. This is still a good example. Or at least, so I believe on the basis of http://bostonreview.net/BR35.2/block_kitcher.php - "These are interesting alternatives to the familiar story, and the causal hypotheses they introduce can be tested in obvious ways: by examining the rates of larvae survival or by investigating nocturnal motions of moths. And this is what biologists have done."
But I don't have time to dig into the primary literature.
"scientists have been interbreeding literally thousands of generations of fruit flies and despite all selection pressures, artificial or not, were never able to produce a single new species"
Thanks, man. Now I have some good resources to refer to when people doubt speciation or macroevolution.
Although this doesn't prove that all species came about through mutation and natural selection only, it does give examples of this happening. I didn't know it happened in plants.
And thanks for setting the record straight on what people believe regarding our common ancestor with neanderthals. Offhand, I thought it was a mere 50k years :P Are there any hominids that split from us more recently? Like 50k?
Remember though that the polyploidy in plants is a fundamentally different process from the way animals speciate. I don't want to mislead you on that point.
um, no it proves the exact opposite. There exist species which have not come about through mutation and natural selection, but rather by artificial selection.
Other points of note: never mind the cellular DNA integrating arsenate, the whole respiration cycle seems to be affected, presumably running on ATA rather than ATP. Which implies huge amounts of molecular booty in the shape of enzymes that are powered by a different reduction gradient (ATA-AMA rather than ATP-AMP).
Possible down to earth applications? Lest we forget, Pakistan has a monstrous problem with arsenic-contaminated wells ( http://www.irc.nl/page/16331 ) and a bacterial culture that thrives on arsenic could offer new approaches to arsenic sequestration. And that's just off the top of my head. (My biochemistry is, alas, too rusty to go much further without a refresher course. Hmm ...)