Several parallel discussions inspire me to write this post partly in the hope that you will chime in.

The chance of life elsewhere in the universe just went to near zero. Or did it?

I was just hanging around minding my own business the other day when someone said to me, “you know, every single one of the five thousand or so exoplanet holding stars found to date have the gas giants in the inner, Goldilocks zone, and the smaller Earth-like planets are too far out to have life. So, the chance of life on other planets is way lower. Zero, basically.”

So, that was depressing.

Then, I went to the opening of the Bell Museum, and watched the planetarium show. After the show, I asked one of the people running the show, a somewhat snotty graduate student from the U, about this news. He got even snottier and told me that was ridiculous, that there are plenty of systems with Earth-like planets in the Goldilocks zone. I asked him how many. Plenty. I asked him if the number was double digit percentage or single digit percentage. He said may be single, but that was enough. I told him I had heard zero, which is not many. He said that was wrong.

Just a few minutes later, on visiting the rest of the newly opened museum, the penny dropped.

It turns out one of the major faculty members at the U in astronomy is one of the planet hunters, and a huge portion of the overall universe level exhibitry in the museum is devoted to showing this one guy’s work and talking about exoplanets and stuff. That must have been his student. Clearly, I had stepped in a pile of something.

My question is, a pile of what, exactly? Is there really recent research that suggests that the Earth’s solar system is unique among a sample of 5,000 or so? Or not? Or what?

The origin of life vs evolution

A long time ago, maybe 20 years now, some evolution-believing but sympathetic to religion people decided to say that the origin of life is not really in the purview of biology, and therefore should not be addressed in textbooks, high school courses, etc. You can think whatever you want about the origin of life, but it has nothing to do with evolution.

I’ve written about this. See:

“We can know nothing about the origin of life”
Is the origin of life different from evolution?

More recently, I find myself repeatedly being dragged into Twitter arguments between people saying that the origin of life is separate from evolution, vs. not.

The reason to say that they are separate is to allow religious people to have their god of the gaps, in this case, the ultimate gap. The pre-life gap.

The conception involves a very serious misconception about what the word “evolution” or the term “evolutionary biology” refer to. Most people misunderstand this.

I’ll give you an example. I was at a conference many years ago at the original Bell (not the one that just opened) and a well meaning but not well informed science teacher said to a room full of science teachers, “Evolution is simple. It is simple to teach. All evolution is…” then he proceeded to lay out the three Necessary and Sufficient conditions for Natural Selection.

Unfortunately, that is not what evolution is, and even more dramatically, it is not what evolutionary biology is about.

Evolution is the change over time in organisms, no matter how that happens.

Evolution is the idea of common ancestry and differentiation of lineages form common ancestors.

Evolution is increase of diversification over time, speciation, and extinction.

So that is three or four, maybe five things, depending on how you count them, that evolution is, and none of them need involve natural selection.

Oh, and natural selection is also part of evolution.

The point is this: If you think evolution is only this one thing, and define it very narrowly, then it is easy to figure that the origin of life is not part of evolution. But evolutionary biology is really the study of life in general, and all of it, in the context of evolutionary theory, and evolutionary theory involves everything from how molecules selectively interact (in primordial soup and in cells and other places) to how genes mutate, to how populations randomly drift genetically apart, or interact genetically, to how coeval lineages of organisms affect each other’s evolution (co-evolution), to how life and non life interact, to how natural selection creatively shapes life.

Evolution and evolutionary biology are two terms that refer to a thing and the study of a thing that is whopping big and complicated and wonderful and amazing and confusing and only barley understood.

To say that the origin of this thing is somehow separate is idiotic.

But to underscore the stupidity of this idea further, allow yourself to consider the following idea as possibly true.

Life evolved more than once.

Even more amazing an idea, and a very interesting hypothesis that we hope one day to test:

Under certain conditions, which are not uncommon in the universe, life almost inevitably arises, just as under certain conditions, a crystal is likely to form, rain is likely to fall, or a fire is likely to ignite. Life, in other words, happens.

If that is true, then the multiple origins of many life systems is clearly of no small interest to evolutionary biologists, and is very much part of “evolution.”

Which brings me to my third thought.

Life evolved independently on Mars, Earth’s Moon, Earth, and who knows where else. Or not.

There is a study just out published in Astrobiology, by Dirk Schulze-Makuch, that addresses part of this. I’ve asked for a copy of the paper, and if I get it, I’ll tell you about it. Without the paper, all I have is the breathless press release, and I’m not going to report on that.

But I can tell you that the basic idea seems to be that there is vague isotopic evidence of past life on the Earth’s Moon, and reconstructions of the Moon’s history suggest that at some point after its formation, and another time later when it was very volcanic, there would have been pools of water, an atmosphere, and some degree of protection from radiation, so life could have been there.

I’m of the belief that life is not that hard to get started. Why do I think that? Because it isn’t that hard to maintain it. Bacteria, especially, survive and do well under a wide range of conditions. A very simple virus can exploit cellular machinery pretty easily. Even though conditions on the early Earth were probably pretty tough, bacteria seem to have arisen early and held on — or perhaps re-started? — for a very long time. This is little more than a gut feeling, but it seems to me that life starting up isn’t that unlikely of an event, given the right conditions.

The reason we don’t see life originating again and again on our planet now may be because the startup does poorly in aerobic conditions. It may be because any molecules that start to form up in a way that leads to life are inevitably tasty food for existing life. Hell, there may be life almost starting up all the time in some places, and then being guzzled up by bacteria of some sort. And there are people looking for that sort of thing so maybe we’ll find that eventually.

Here’s my question on this. Which is harder to see happening, harder to believe, harder to accept, given what we know, and what we like to guess, about life?

1) Life started once, say, on Mars, and that’s it. Just that one time. Life found later on the Moon or on Earth came from Mars by a large rock hitting life-bearing mars, spreading rocks across the inner solar system, and some of those rocks eventually landed on the Moon and Earth, burning to a crisp in the atmosphere but somehow the bacteria on the rocks survive.

or

2) Life starts up easily and did so on Mars, the Moon, and Earth. For the first two, conditions for life were transient and have ended. For the Earth, conditions for life are a bit longer lived, and will end later.

Yes, yes, this all assumes there was life on Mars or the Moon, and we simply do not know that to be true at this time. This argument only matters if we pretend it was true, or at least possible. So this is speculation.

The Nuvvuagittuq belt in Quebec is a geological formation that includes such rock.

There are two basic ways to identify a tiny bacteria like life form. Well, sort of three. Method 1 is to find a physical structure that looks like the life form. So, little bacteria shaped do-dads might be bacteria fossils. Method 1a would be to find that, method 1b would be to find something slightly less direct, such as stramotlites, which is a kind of rock formed from the accumulation of bacteria byproducts. Method 2 is to look at the isotopes of key elements, usually carbon. There are a lot of ways for carbon to get mixed up in a rock. But, the non-life connected sequence of events that put carbon in a rock would sample the ambient carbon in a characteristic way. Since carbon comes in more than one stable isotope, the stable isotope ratio of the carbon in the abiogenic rock would reflect this pattern. But living systems tend to use carbon in a different way. The carbon atoms that get used by the tiny molecular processes involved in assembling molecules are biased in which carbon isotope they end up using. This results in a carbon isotope profile different than the expected ambient one, and suggests life.

Today in Nature, a paper by Matthew S. Dodd, Dominic Papineau, Tor Grenne, John F. Slack, Martin Rittner, Franco Pirajno, Jonathan O’Neil, and Crispin T. S. Little entitled “Evidence for early life in Earth’s oldest hydrothermal vent precipitates” (Nature 543, 60-64) reports, from the abstract:

… we describe putative fossilized microorganisms that are at least 3,770 million and possibly 4,280 million years old in ferruginous sedimentary rocks, interpreted as seafloor-hydrothermal vent-related precipitates, from the Nuvvuagittuq belt in Quebec, Canada. These structures occur as micrometre-scale haematite tubes and filaments with morphologies and mineral assemblages similar to those of filamentous microorganisms from modern hydrothermal vent precipitates and analogous microfossils in younger rocks. The Nuvvuagittuq rocks contain isotopically light carbon in carbonate and carbonaceous material, which occurs as graphitic inclusions in diagenetic carbonate rosettes, apatite blades intergrown among carbonate rosettes and magnetite–haematite granules, and is associated with carbonate in direct contact with the putative microfossils. Collectively, these observations are consistent with an oxidized biomass and provide evidence for biological activity in submarine-hydrothermal environments more than 3,770 million years ago.

I used to work down the hall from a guy who was involved in the search for early life. I won’t mention names, but at the time, I remember the fighting among scientists about whether or not this or that piece of evidence was legit was pretty intense. I think things have calmed down a bit. Back then, the battle was between Australia and Greenland. These days, apparently, Canada is in the act.

At present, the oldest evidence of life that is widely accepted is probably close to about 3.0 mya, with several older sites in contention. The newest find, as noted, dates to between 3.77 and 4.28 billion, and I understand the dates are somewhat controversial. If this site ends up as representing early life, it may well be the earliest, assuming the date is anywhere in this range. There are other cases that are close to 3.8 billion but the current study’s argument may be stronger. Over the last few years, the very nature of the study of early life on earth has gained a significant amount of perspective and methodological philosophy which I think will allow future work to be considered more sensibly. By this, I mean, that rather than asserting that this or that evidence is certainly indicative of early life vs. not conclusive (or not evidence of life) we will start seeing a more unified characterization of early environments and conditions, along side a better set of models for how life could originate. In that context we may never have an “earliest life” fossil, but we may have a much better story to tell about how early life could start.

I’ll add this: Consider the number of scientists working on a problem like aging in muscles, or how to attack a certain kind of cancer. Tens of thousands. Now, consider the number of scientists dedicated to working on the origin of life. Not many. Given the magnitude and difficulty of the problem — in the field, in the lab, and in the theories — there is no wonder it is taking science many decades to nail this problem down.

And, no, the origin of life is NOT different from evolution, no matter what the creationists tell you.

See: The Story Of Life in 25 Fossils by Don Prothero: Review

Let’s start off with a kid’s book: Grandmother Fish: a child’s first book of Evolution by Jonathan Tweet.

From the blurb:

Grandmother Fish is the first book to teach evolution to preschoolers. While listening to the story, the child mimics the motions and sounds of our ancestors, such as wiggling like a fish or hooting like an ape. Like magic, evolution becomes fun, accessible, and personal. Grandmother Fish will be a full-size (10 x 8), full-color, 32-page, hardback book full of appealing animal illustrations, perfect for your bookshelf. US publishers consider evolution to be too “hot” a topic for children, but with your help we can make this book happen ourselves.

I reviewed the book here before it first came out. This was a kickstarter project, and it may be currently unavailable commercially, but if you click through to the kickstarter project you can probably get a copy of it.

The most recent book to come across my desk is Don Prothero’s The Story of Life in 25 Fossils: Tales of Intrepid Fossil Hunters and the Wonders of Evolution. I’ve got a review of Prothero’s book in my draft file, so look for that post coming out over the next few days.

One might ask, “how do you choose 25 fossils, among so many choices, to represent evolution?” Well, Don cheated a little by mentioning more than 25 fossils. Also, you really can’t do this. Don selected fossils using several criteria, but one basis for his choice was the availability of rich historical information about a fossil’s discovery, interpretation, and effect on our thinking about evolution. And, he covers all of that.

Don is one of those rare authors who is both an expert scientist and a great writer, with a proven ability to explain things in a way that is not watered down yet totally accessible.

Here’s a selection of the many other books written by Prothero:

• Abominable Science!: Origins of the Yeti, Nessie, and Other Famous Cryptids

• After the Dinosaurs: The Age of Mammals (Life of the Past)

• Catastrophes!: Earthquakes, Tsunamis, Tornadoes, and Other Earth-Shattering Disasters

• Greenhouse of the Dinosaurs: Evolution, Extinction, and the Future of Our Planet

• Rhinoceros Giants: The Paleobiology of Indricotheres (Life of the Past)

• Evolution: What the Fossils Say and Why It Matters by Prothero, Donald R. 1st (first) Edition [Hardcover(2007)]

Evolution: The Whole Story is an astonishing book that needs to be on the bookshelf of anyone interested in evolution. The work is edied by Steve Parker, but authored by nearly a dozen experts in various subfields of fossils and evolution, so it is authoritative and scholarly. At the same time, it is very accessible and enjoyable. This is not a book you read from cover to cover, though you could. Feel free to skip around, and you;ll find yourself looking stuff up all the time.

The book is divided into major sections, and each section has a series of short pieces on this or that fossil, group of fossils, type of life system, method for studying fossils, etc. There is a running sidebar on the bottom of many pages giving “key events” in evolutionary history of the group of life forms under consideration The book is VERY richly illustrated, with detailed keys to the illustrations. Many of the illustrations are broken down into “focal points” that expand significantly on the illustrations’ details. There are countless additional inserts with more information. The book itself is beautiful, intriguingly organized, and it is full of … well, everything. The book is very well indexed and sourced, and has helpful, up to date, phylogenies and chronological graphics.

The Biology Book: From the Origin of Life to Epigenetics, 250 Milestones in the History of Biology (Sterling Milestones) by Michael Gerald and Gloria Gerald is a compendium of biological topics and key moments in the history of biological science, organized in a sort of chronological framework. Major groups (the insects, the amphibians), major ideas (Pliny’s Natural History, Ongogeny and Phylogeny), key physiological and developmental concepts (meiosis, mitosis, many topics in endocrinology), key fossils (like the Coelocanth) and so on are discussed, very nicely illustrated. This is almost like having a gazillian short articles from Natural History Magazine (or similar) all in one book. There are 250 biological “milestones” in all. The charming part of the book is that a milestone can be an evolutionary event, an extinction episode, the emergence of a great idea, or a particular discover. And, as noted, these are ordered across time, as well as one can, from the beginning of life to a selection of the most recent discovery. The book effectively combines history of biology (and related sciences) and the biological history itself.

Life’s Greatest Secret: The Race to Crack the Genetic Code by the well respected scientist and historian Matthew Cobb is a carefully and clearly written history of the discovery of the nature of DNA, covering a lot more than, and since, Watson and Crick. It is extremely well sourced, indexed, and supported, and very readable.

This is the detailed and authoritative work on all the elements that came together to understand the genetic code. Don’t talk about the discovery and understanding of DNA any more until you’ve read this book. From the publisher:

Life’s Greatest Secret mixes remarkable insights, theoretical dead-ends, and ingenious experiments with the swift pace of a thriller. From New York to Paris, Cambridge, Massachusetts, to Cambridge, England, and London to Moscow, the greatest discovery of twentieth-century biology was truly a global feat. Biologist and historian of science Matthew Cobb gives the full and rich account of the cooperation and competition between the eccentric characters—mathematicians, physicists, information theorists, and biologists—who contributed to this revolutionary new science. And, while every new discovery was a leap forward for science, Cobb shows how every new answer inevitably led to new questions that were at least as difficult to answer: just ask anyone who had hoped that the successful completion of the Human Genome Project was going to truly yield the book of life, or that a better understanding of epigenetics or “junk DNA” was going to be the final piece of the puzzle. But the setbacks and unexpected discoveries are what make the science exciting, and it is Matthew Cobb’s telling that makes them worth reading. This is a riveting story of humans exploring what it is that makes us human and how the world works, and it is essential reading for anyone who’d like to explore those questions for themselves.

Extinction and Evolution: What Fossils Reveal About the History of Life is a an updated version of a classic book about evolution and extinction written by one of the scientists who developed our modern way of thinking about evolution and extinction (especially the extinction part).

Eldredge’s groundbreaking work is now accepted as the definitive statement of how life as we know it evolved on Earth. This book chronicles how Eldredge made his discoveries and traces the history of life through the lenses of paleontology, geology, ecology, anthropology, biology, genetics, zoology, mammalogy, herpetology, entomology and botany. While rigorously accurate, the text is accessible, engaging and free of jargon.

Honorable Mentions: Older books that are great and may now be avaialable for much reduced prices.

I really liked The Great Transition: Shifting from Fossil Fuels to Solar and Wind Energy as an expose of a particular time period and major event in geological history. Greenhouse of the Dinosaurs: Evolution, Extinction, and the Future of Our Planet by Prothero is a classic, again, looking at a fairly narrowly defined moment in prehistory. You can get it used for about five bucks.

The Fossil Chronicles: How Two Controversial Discoveries Changed Our View of Human Evolution by Dean Falk is a great book focusing on one key human fossil. This is a personal story as well as a scientific one. Again, available used for a song.

Have you read Your Inner Fish: A Journey into the 3.5-Billion-Year History of the Human Body yet? I’m sure you’ve heard about it. It is still a great read, and you can get it used cheap.

The only book I would recommend that uses the “paleolithic” to advise you on diet and exercise is The Paleolithic Prescription: A Program of Diet and Exercise and a Design for Living.

That’s pretty darn convincing. Until someone opens up some closed thing and there is some new species in there, then EVOLUTION IS MADE UP!!!1!!!

Well, it turns out, Evolution is True. Some guy on the internet opened up an Oreo Cookie and inside was a new organism that could only be there IF IT EVOVED IN SIDE THE COOKIE!!1!! Look here’s a picture:

A fake you say? A falsehood you say? Sorry, but Snopes was unable to disprove that this spider appeared spontaneously inside this cookie. Indeed, we all know that stuff that can’t happen happens all the time. If anything, Snopes will declare something false even when they can’t, so clearly, this spider did evolve in this Oreo Cookie.

Evolution. It’s real.

BTW, if this happens to you and creates a spider problem in your house, we can fix that.

Imagine that dozens of shallow seas of primordial soup on this planet each produced a range of such things, and they moved around on the planet, some staying in the soup, some going onto land, interacting, competing, cooperating, eating each other, sliding past each other, being born of the soup and dying, the dust sometimes being blown back into the soupy seas or being scraped up by other things.

The things are alive, right?

What if there was a form of thing on some other planet that had crawled out of the ooze and over time evolved, changed, varied, but over even longer periods of time, a self replicating version of this thing, or set of things, developed a way of perfectly identifying copies of itself that were not perfect, and destroying them. Say this emerged in several lineages of things, and this invariance gave some advantage to the things that did this. All other things, the ones that vary and change over generational time, are out-competed and those lineages disappear. So eventually, there are dozens of lineages of distinct but invariant things walking, sliding, coasting, flying, around on the surface of this planet, replicating but always duplicating perfectly, for hundreds of thousands of generations.

These things are alive, right?

Not according to Edward Trifonov, who defines life as:

“self-reproduction with variations.”

Carl Zimmer has written up a nice piece on the definition of life and in particular the work done by Trifonov (Can A Scientist Define “Life”? By Carl Zimmer). Go read it.

In essence, and you can get the details from Carl’s writeup, Trifonov has done a linguistic analysis of the hundreds of definitions of life previously available and distilled them down to their essence to produce the most functional and applicable definition of life.

Except it isn’t, for three reasons.

1) The search to understand what life is, and possibly find it elsewhere (or forms on earth of which we are currently unfamiliar) is not about finding something we know about, but rather, it is about finding something we don’t know about. By looking only within the stated definitions, we might find a nice linguistic analysis but we’ve limited our definition to a set of criteria less than that which has already been considered. This definition systematically turns its back on the newness that is almost always out there in exploratory science;

2) The simplest distilled definition that is, essentially, the most overlapped part of a set of complex interconnected Venn diagrams, is probably going to leave out details we’ve already thought of, that we were not sure at the time were important, and that may end up being very important, and may even end up being the key nuanced thing that makes both life itself and the definition thereof work; and

3) I just disproved the definition by imagining two universes that you would be hard pressed to disprove exist. I know, I know, I might as well have suggested “Unicorns are born of rainbows” or something, but still… this is a big and long-lived Universe and something that we would call life that does not vary in it’s replication, or that emerges from something we don’t call life such as a Droid or Robot might emerge but where the robot-maker is not a high tech company but rather a puddle, are not outrageously impossible. OK, so maybe I didn’t disprove it, but I made it look weak, don’t you think?

Zimmer also makes the point in his piece that some have questioned the smarts behind NASA going to Mars to find life using an Earth based model, whereby life will exist in relation to water and carbon. I agree with him that life in the Universe may ignore such Earthly rules. However, it is true that Mars is fairly Earth-like, and there is water there, so given the limits on what we can do with remote control robots on other planets, testing the hypothesis that “Mars has or had a roughly Earth-like life” is not too unreasonable. Personally, I think they’ll find it. After all, the only other Earth-like planet we’ve looked at so far has it!

But that is not actually how it works, and the best way to think about this is to ask the following question: “Just what do you think evolution is?”

Possible answers would be “Evolution is natural selection,” or “Evolution is the diversification of species,” or “Evolution is change organic change over time” and so on. These are all correct, of course. But if evolution is any two or more of these things, then it is not one of these things, exclusively. And, if evolution is both diversification and natural selection, then it is a concept that includes some very very different things. So, if you think “Origin of Life” is not evolution because it is somehow different from any one specific aspect of evolution (like natural selection) then you are being unfair to Origin of Life by treating its different-ness as an excuse for excluding it. Shame on you.

It seems that one argument is that the Origin of Life is not evolution because evolution is natural selection, diversification of species, and so on, and none of those things could have happened without life already existing, and it does not really exist at the moment of origin. This, however, is not correct for two reasons. The first (and probably most important) reason is that we don’t know what the origin if life was like. So, to characterize it as an instant when some stuff goes from being not-life to being life is fantasy. You don’t know that this is how it happened, so you can’t use this made-up trait of the origin of life to say that it is not evolution. The second reason is a bit more tenuous; Most models for the origin of life are very Darwinian. Most have some selection going on, most have some diversification going on, and all, by necessity and definition, have change over time going on. And, it is organic change, because the stuff of life before the primordial animation was organic stuff.

The origin of life is part of evolutionary biology.

Anyway, not far from this spot, in Lester Park, one finds this rock:

This is “stromatolite.” Blue-green algae, a.k.a. bacteria, generates a “biofilm” that probably has a number of purposes, including managing moisture and protecting the cells from UV light. You know this stuff. If you leave water in an open glass long enough you’ll get a slimy surface on the inside of the glass. Perhaps you get a dark gray (or some other color) film in your toilet bowl, and certainly, there is a fuzzy slimy coating in the reservoir in the back of your toilet. Go to a lake and look at the stuff forming on the rocks that isn’t a plant. Most of that stuff is biofilm.

Cyanobacteria, Cyanophyta, blue green algae, blue-green amd bacteria are all different names for the same phylum of bacteria. Other bacteria make biofilms as well, but the cyanobacteria (or something very much like cyanobacteria) were at one time the dominant organism on the planet, and lived on the surfaces of anything covered with enough water on a regular basis to make it possible to stay wet, but not enough water to shade it from the sun. These are the organisms that altered our atmosphere to be oxygen bearing instead of oxygen poor, according to most prevailing theories of early life on earth.

Before things like snails (snails are only the most modern form of creatures like this) cynobacteria living in shallow seas developed bioflims over long periods of time, and these biofilms built up, and trapped bits of sediment, to form stramotlites. Here’s some more pictures:

Snails and other creatures evolved later and ate both the blue-green algae and the biofilms. Therefore, today you don’t see a lot of stromatolites formation.

So, in case it isn’t already obvious, this is the cool think about stromatolites: They exist only in ancient contexts, and as fossils, but are the outcome of a process that is very much current, but because of the creatures that eat the algae and the bioflims, stromatolites stopped forming very very early in the history of life.

Almost. In fact, stromatolites still form and probably have formed off and on, here and there, under certain rare conditions. For example, in Shark Bay, Australia. This is an arid patch of ocean partly embayed on the west coast of Oz where evaporation is sufficiently rapid that the water is hyper-saline. The hyper-saline conditions make it impossible for snail-like cyanobacteria-eaters to be abundant. Therefore, there are active “living” stromatolites there.

The Lester Park stramotlites formed in a rather large shallow sea now known as the United States, a few years back (more info on that here).

I came across the above photos that I had taken on that day, years ago, with the geomancer. Thought you might enjoy them.

Here’s some more info on Lester Park: Lester Park (New York State Museum)

All life on earth descended from a single, original, primordial form that arose eons ago.

The evidence in favor of this hypothesis is strong, but the test of the hypothesis … the means of disproving it, which is, after all, the point of stating it to begin with … is difficult to define, but like pornography to a judge, one would know it when one sees it.

The question at hand is, does the current finding reported moments ago by NASA relate to this concept at all? The answer, as you’ll see, is yes. And no.

The evidence for a single origin is this: There are a lot of potential variations in how life works, but only a very small and rather quirky subset of those variations exists in every known organism on this planet, strongly suggesting a single origin which left, as a sort of timeless imprint, that selectivity and quirkiness. Hundreds of amino acids are known to exist, but only 20 are used as the basic building blocks of life. The genetic code (the codons that specify those building blocks) is odd and quirky, but exists with very little variation across all lifeforms. Certain complex molecules, most notably the ribosomes that are key in forming complex molecules such as proteins on the basis of the genetic code, are large, clunky, and made up of sequences that could easily be very different than they are and still work, but nonetheless follow a very limited pattern, strongly suggesting that all existing forms have but one ancestor. DNA itself is pretty much the same everywhere, suggesting, again, a single origin.

If life arose on Earth more than once, there would likely be more than one quirky, finger-print like pattern of coding, building blocks, and complex molecules. And there isn’t. Right?

Well, if you’ve read my blog long enough, you probably know that I would not have explained all of this if there was not some way to turn around and explain how it’s all wrong.

First, we have the latest news from NASA. It turns out that there is a form of life that is different, in a very fundamental way, from all other life forms on the planet. It is a bacteria-like form that appears to be able to use arsenic instead of phosphorous in forming its DNA, and probably in other functions as well, known by the term “strain GFAJ-1 of the Halomonadaceae” (hereafter referred to as “the bacterium”). Given the model I’ve just described, this is a potential falsification of the Darwinian hypothesis that life originated once.

Now, before we go all “Darwin-was-wrong!!!11!!” on this, let me be very clear: This hypothesis … that all life has a single origin … is singularly unimportant to overall Darwinian or Evolutionary theory. If, indeed, life originated different times and different places so that today there were different environments (or continents, or whatever) with diversified forms of each separate origin, that may have been noticed by Darwin (or later biologists) and the multi-origin would simply be a fact. If each set of life types had diversified into different species and otherwise been very Darwiny in history and behavior, with Natural Selection working in all the distinct lineages, etc., the other four of Darwin’s theories (as told by Mayr) would be very strongly supported, because Darwinian processes would be seen to play out in multiple instances. Similarly, if we find that life started up at different times and different places elsewhere in the universe (on other planets) then this would address similar questions. Who knows? There may even be non-Darwinian life forms that arose in a certain pattern and never changed thereafter. Darwinian evolution requires that imperfect copies are made each generation. A life form that copies itself perfectly, or one in which imperfection always leads to termination of a lineage, would never posses the variation that Natural Selection works on. You can see why the discovery of extra-terrestrial lifeforms would be very interesting to biologists!

But I digress, somewhat. What we have now is a proposal that all life on Earth has the same origin because all known forms have the same somewhat to very quirky variants in how they work that act as an individual, unique fingerprint pointing to one origin. The Mono Lake find, however, is an organism with at least one aspect of that quirky how-life-works pattern that is different. Does this falsify the Darwinian hypothesis?

The Mono lake life form is a bacterium. A team of scientists started with a culture of bacteria from Mono lake, an utterly inhospitable environment in California (near Nevada, east of the Bay Area) in which life seems to thrive against the odds. This was placed in a medium that contained all the necessities of bacterial life, to allow the bacteria to be alive, to thrive, to grow, and to reproduce, except phosphorus. This soup also contained a high level of arsenic.

They did this because the lead scientist on the team, the Carl Sagan-like Felisa Wolfe-Simon, was considering the preposterous idea that arsenic could substitute for Phosphorus in some biological systems. There were no known cases where that actually happened, but arsenic does in fact replace phosphorus very easily, which is why it is a poison for many organisms. If you put together the elements that make up key organic molecules in a test tube and shake it, usually nothing happens unless there is a set of other molecules (enzymes) and some ATP and stuff to make it assemble as it should. But if you put arsenic instead of phosphorus in the same soup, you get at least partial reactions that look like the formation of organic structures. In other words, given an atom of arsenic and an atom of phosphorus, the arsenic had a better chance of insinuating itself into certain key positions than the phosphorus element. Also, arsenic is more reactive than phosphorus.

Here’s the thing: Phosphorus is often used in molecules in places where it provides important stability, once it is in place. It forms the very backbone that keeps the DNA molecule together. If arsenic, chemically similar to phosphorus but more reactive, is accidentally substituted, the stability is compromised. Arsenic is such an effective poison for this very reason. It’s like a suicide bomber dressed like a security agent. It easily gets into an important location, then it ‘reacts’ with stuff and messes everything up.

But owing to some sort of brilliant insight, Wolf-Simon thought arsenic could sometimes substitute for Phosphorus, and she reasoned that the best place to find that biological difference would be in organisms that had evolved in a place where there was a LOT of arsenic, yet life still existed despite the presence of this nominal poison.

Thus the experiment. And it worked. Even in the absence of phosphorous, in an arsenic rich environment, a bacterium thrived. (This is an oversimplification, but that is the general idea.) When they looked more closely, they discovered that the arsenic had substituted for phosphorus in part of the DNA of the bacterium.

Now, consider for a moment (but no longer than a moment) a life form that uses arsenic instead of phosphorous. As the backbone of the DNA, as part of the energy-system molecules of ATP, and elsewhere, arsenic is used instead of phosphorous. That would be a life form that had a quirk that was distinctly different from the usual finger-print like quirks that generally convince us that all life has a single origin. It might be an organisms that evolved from a separate origin.

Is that the case here?

No, I don’t think so, but there are two ways in which this finding can inform and guide research into the possibility of multiple origins of life on earth.

It has not yet been demonstrated that arsenic substitutes for phosphorus in all reactions in these bacteria. The bacteria could have had some of their own phosphorus, and only most but not all was substituted. It also seems that this organism uses arsenic in a facilitative rather than obligatorily manner. In other words, this bacterium uses phosphorus in the usual way, but can substitute arsenic under certain conditions. Also, it has not been demonstrated that the other quirky bits of the inner workings of the cell are different from the norm in this organism. So, it would appear that this is a bacterium that has secondarily evolved a trait, viable substitution of arsenic for phosphorus, and not a separate lineage.

There are two (really, three) ways that this finding could speak to Darwin’s second theory.

One is that the above is wrong … that it will be discovered that this “bacterium” has a different ribosome, and other differences, and really is a different form of life that originated separately from the rest of life on earth, but has not been investigated closely enough yet to know these things. My reading of the paper and observation of today’s press conference at NASA makes me think not, so let’s leave that one aside. Maybe we’ll be shocked later on this issue, but I think not.

So, the other two ways in which this finding relates to Darwin’s second theory are 1) This could suggest a high diversity of life forms early in life, which could mean that the origin is not a point so much as a committee of diverse experiments that finally settled on the current system of double-helix phosphorus-spined DNA, RNAs, ribosomes, and so one and 2) By demonstrating that an entire life system could use arsenic and not use phosphorus at all.

The first of these may be a bit esoteric, but nonetheless interesting. What I’m suggesting here is that the origin of life involved several different biochemical experiments that would now and then spatially overlap, and when they did so, sometimes combined. There may have been arsenic based systems and phosphorus bases systems, and they may have combined at different times and places, and most life subsequently evolved from a subset of these different bowls of primordial soup. One of those primordial soup bowls happend to be just like all the others but for the bit about arsenic. The test of this hypothesis (a partial test, anyway) would be to reconstruct the phylogeny of this bacterium. Did it separate from the other bacterial lineages at a time near the origin of life, or much more recently? Wolfe-Simon and her team are at present not saying anything about the phylogeny of this bacterium, and when asked about it at the press conference indicated that they just don’t know yet.

The second idea is more likely, and relates closely to the thrust of the research team’s presentation in their paper and in the press. At a large scale, arsenic substitution for phosphorus simply means that we should not be ignoring phosphorus-poor arsenic-rich environments on other planets. At en even larger scale, we should consider that other substitutions are possible (silicon for carbon is a common idea along those lines, at least in science fiction!).

But with respect to life’s origins on earth, related to Darwin’s second theory, there is a more direct implication that I think would be easy to explore. Irregardless of the phylogenetic position of this particular bacterium, its existence today suggests the possibility of the existence of something like it in the past. So, the question is, biochemically, is there either a stage in the origin of life in which arsenic is the key element for certain chemical activities in stead of phosphorus, or, more interestingly, can we find populations in one part of the ancient earth (as fossils, of course) of phosphorus based bacteria and other populations, in different geological regions, of arsenic-based bacteria, living contemporaneously?

Get cracking, ancient biochemists!

Wolfe-Simon, Felisa, & Et.Al. (2010). A bacterium that can grow by using arsenic instead of phosphorus Science : 10.1126/science.1197258