SETI: Let the Search Continue

by Paul Gilster on September 2, 2011

Most people think that SETI is worth doing, whether or not they actually believe there are other technological civilizations in the galaxy. Ben Zuckerman, a professor of astronomy at UCLA, is certainly in the skeptics’ camp, thinking there are no technological ETs in the Milky Way, but he’s quoted in this story from QUEST (KQED San Francisco) as calling for more SETI. “Given that the costs are not very high,” says Zuckerman, “why not continue the search?” Zuckerman, who once worked with Carl Sagan in graduate school, no longer thinks we live in a crowded galaxy, but a potential discovery of this magnitude justifies the relatively modest expenditure.

It’s not surprising to find Jill Tarter echoing Zuckerman. The recent funding problems of the Allen Telescope Array have not daunted the woman who more than anyone else has come to represent the search for other intelligent life. And although she believes we may one day come to the ‘extraordinary conclusion’ that we really are alone, the time for drawing that conclusion is hardly near. We have hundreds of billions of stars to choose from in the Milky Way and hundreds of billions of galaxies beyond our own, and in those terms, we’ve barely begun to search.

Image: SETI searcher Jill Tarter. Credit: Sven Klinge.

The KQED story takes note of the new element in SETI research, which has to do with the Kepler mission. With the discovery of more than a thousand planets orbiting stars in its field of view, Kepler may well have found the first true Earth analogues — we’ll know as its data continue to be analyzed. The Kepler findings give us a targeted list of stars that should be high priority for the SETI hunt. “This,” says Kepler team member Dimitar Sasselov, “is where we should be looking for the signals coming from other civilizations.”

Just a month after the hibernation of the Allen Telescope Array due to money problems, the Green Bank radio telescope facility in West Virginia announced its own effort to study 86 of the stars chosen from the Kepler list, scanning an 800 mHz range of frequencies simultaneously (that’s 300 times the range available at Arecibo). Among the 86 stars Green Bank will be studying are 54 candidate systems identified by Kepler as potentially having a planet in the habitable zone. Thus the largest steerable radio telescope in the world picks up on the Kepler work, another case of SETI soldiering on when resources are scarce.

And fortunately, the Allen Telescope Array itself is back in business, thanks to more than $200,000 in donations from some 2400 donors and an infusion of money from the U.S. Air Force, which should keep the project running for the next several months. In the longer term, the ATA needs $2.5 million per year to keep operational, so fund-raising will doubtless become a permanent fixture of the facility’s operations. The SETI Institute’s page supporting a search of the Kepler candidates using the ATA continues to gather donations, a reminder that while SETI may be for now a relatively low-key project, it’s one that generates wide public interest.

Image: A single antenna of the Allen Telescope Array, night. Credit: Allen Telescope Array.

My own views on SETI parallel those of Ben Zuckerman. I doubt intelligent life is widespread in the galaxy, but the whole point of science is to extend our knowledge. By all means, let’s keep SETI in business, and maybe we skeptics will be proven wrong. And just letting the imagination run, it’s fascinating to ponder the world we might live in if one of the Kepler planets turns out to be leaking some kind of artificial radiation. Remember that Kepler is looking out along the Milky Way’s Orion arm, in an area where fewer than one percent of the stars the mission examines are closer than 600 light years. If we were to detect a transmission, it would take 1200 years to receive any return to our potential response. I suspect a detected signal, after revolutionizing our view of ourselves in the cosmos, would probably remain unrepeated and untranslatable, a mystery for our time, an enigma speaking of all we have yet to learn.

tzf_img_post

{ 125 comments }

Bob Steinke September 12, 2011 at 11:24

@eniac

“Funny, I almost wrote earlier that it does NOT deserve the name paradox. It is simply evidence for one or more of the Drake factors to be very small. To me, it is not problematic at all. We have a lot of options left. My bet would be on fl as the most plausible to be small.”

It’s problematic because when we try to estimate each factor in isolation we don’t come up with any factor that should be very small unless Earth is atypical which, as Ronald said, violates the cosmological principle that we aren’t anything special.

In the case of fl, (from Wikipedia) “In 2002, Charles H. Lineweaver and Tamara M. Davis (at the University of New South Wales and the Australian Centre for Astrobiology) estimated fl as > 0.13 on planets that have existed for at least one billion years using a statistical argument based on the length of time life took to evolve on Earth.”

Since we don’t see aliens our estimates for one or more of the factors must be wrong, and now we’re meta-arguing over which factor would require the Earth to be the least atypical. It might be fl.

But I still think it deserves the name paradox because we know for sure that at least one line of reasoning that to us looks right must be wrong.

kzb September 12, 2011 at 13:21

Eniac wrote:
Funny, I almost wrote earlier that it does NOT deserve the name paradox. It is simply evidence for one or more of the Drake factors to be very small…

However, if certain of the later factors are indeed very small, it does not say much for OUR future.

If you posit that that fc is tiny or that L is very short, what you are saying is that all previous civilisations in the galaxy have failed in short order. If you also hold with the Earth-is-typical viewpoint, that logically means that OUR civilisation will also fail.

So you may as well forget about the whole point of this website, because none of it is going to happen. That’s the logical result of this chain of reasoning.

Rob Henry September 12, 2011 at 18:24

Many seem to put the Fermi paradox synonymous with the Great Silence. Fermi’s original question simply pointed out that IF the Milky Way contained MANY ETI’s their presence should be immediately apparent to us. Why is there felt a need to recast it in a SETI friendly way where our own intensive input is first required?

Eniac September 12, 2011 at 20:37

Bob, Ronald: I do not see a contradiction between “fl is small” and “Earth is typical”. In fact I think both are perfectly satisfied if fl is small on any of a billion planets. It is small the same way on every planet, so there is no violation of the cosmological principle.

And the argument that it must be large because we are here is faulty, because if we were not here we would not be able to perceive the opposite. In other words, our “observation” of a large fl is biased by our inability to observe the cases where life did not occur. In statistics, this is also called “censoring” and is a well-known generator of bias.

Rob Henry September 13, 2011 at 17:45

I quote Bob quoting Wikipedia “In 2002, Charles H. Lineweaver and Tamara M. Davis (at the University of New South Wales and the Australian Centre for Astrobiology) estimated fl as > 0.13 on planets that have existed for at least one billion years using a statistical argument based on the length of time life took to evolve on Earth.”.

So, noting their methods, you might think that IF there was at least a 95% probability that the chance of abiogenesis was even with time and the Earth typical AND IF one billion years is the window of time typically available without biasing the chance that intelligent observers can evolve thereafter THEN our best current data puts it probable that fl > 0.13.

The following year Lineweaver and Davis felt it necessary to redo their calculation and found that, with the same above caveats, fl > 0.38.

Eniac September 13, 2011 at 21:11

I would bet Lineweaver and Davis neglected to consider the effect of censoring, a common pitfall in statistics.

Rob Henry September 13, 2011 at 23:55

Eniac, I can’t speak to the details of their first paper, but in their second they thought of taking censoring into account. To compensate they needed to know how much more time complex life could continue to evolve for on Earth. Estimates were difficult and varied widely, but they thought it sufficiently evident that whatever time was left for such developments, our present knowledge would place it as much larger than the time from Earth being receptive to life till life’s origin. Consequently, they concluded that no adjustment was needed.

There seems little doubt to me that, in the (unlikely) event that the probability of life’s first appearance on a dead planet does not trail off with time, their case is solid.

Avatar2.0 September 14, 2011 at 11:06

Eniac

“Let me try to paraphrase, to cut through the argumentative and capital-enriched fog:
Avatar, you assume organisms cannot move into and compete in other niches.”
Actually, I assumed the contrary –
The first protein life form will replace RNA based life forms ONLY in its niche, because it cannot move into and compete in other niches. ”
If I paraphrased correctly, you have an unusual way of using the word “contrary”. Perhaps you could point out where I misunderstood.”

If you insist:
“This life form will NOT be in competition with life (any kind of life) which occupies different ecological niches; thus, it won’t replace such life.
See here:
Not for a VERY LONG TIME (until it evolves AGAIN forms which can use these niches – which gives a LOT of time to other trees of life to develop such adaptations).”

“Explanation 1 – life is improbable, so only one tree of life appeared.
Explanation 2 – life is improbable, but more trees of life appeared anyway…”
You forgot the all-important third possibility:
Explanation 3 – life is probable, but we observe only one tree of life because the others either became extinct or were pre-empted.”

So, your third explanation is – life is probable, but life evolving DNA (or another fundamental adaptation) is so unlikely that the first life form (from a tree of life) to develop it will evolve, expanding into other niches (ALL OTHRER NICHES WHERE LIFE CAN EXIST) before another life form belonging to another tree of life will develop a similar adaptation (and we’re talking about a truly geological time span – that’s before the invention of sex).

This third ‘explanation’ merely takes the improbability from life appearing and puts it at life developing a fundamental adaptation.
Do you really think this is the case?

Avatar2.0 September 14, 2011 at 11:19

Gunnar Larsson

“@Avatar 2.0:
Consider the case that your maths was correct. The number of atoms in the universe is likely somewhat less than 10^80, of which only a small fraction is available to form life. The universe has lasted for a bit over 10^20 seconds. Reaction rates obviously depend on the local circumstances, taking N2 and O2 in air as a rough guide gives a number of about 10^10 reaction/second & atom. In total therefore about 10^110 chemical reactions have taken place in the universe so far (very roughly!). If your maths was correct and relevant the number of times life would have formed would be:

If 100 steps were needed: about 10^-47
If 1000 steps were needed: about 10^-2457
If 10000 steps were needed: about 10^-35549″

There’s one problem with your reasoning, Gunnar Larsson:
There are 10^80 atoms in the OBSERVABLE UNIVERSE – which is quite different from the entire universe – and when we’re talking such probabilities the entire universe is relevant.

How large is the entire universe?
No one knows. According to some theories, it’s far larger than the observable universe. Indeed, postulating a universe FAR larger than the one we observe is less wild than postulating parallel universes, 11 dimensions, etc.

This being said, my factorial example is an oversimplification. The real answer to the probability of life may be only in the general (‘general’ being VERY generously defined) vicinity of it.

“Now, we now that the actual number is at least 1.”

’1′ what, Gunnar Larsson?
1 chance in 10 is entirely different from 1 chance in 1000.
In probability, you need something to compare ’1′ to, for ’1′ to have any meaning.

We know the chance of life arising is not 0%, yes, but this chance can very well be as close to 0 as you can imagine – we most definitely do NOT know the chance of life arising is larger than such mind-blowingly small chances.

Eniac September 14, 2011 at 20:17

Not quite. Fundamental adaptation do not need to be improbable at all for this scenario. All it takes is that they spread faster than they reoccur.

Avatar2.0 September 15, 2011 at 1:44

Eniac

“Not quite. Fundamental adaptation do not need to be improbable at all for this scenario. All it takes is that they spread faster than they reoccur.”

And how do these fundamental adaptations spread? The only mechanism – the life form which has them will evolve and diversify until it occupies ALL available niches. THIS TAKES A LOT OF TIME.

And if no other life form (belonging to another tree of life) develops these fundamental adaptations during all this time, then their apparition is highly improbable.

Meaning, in your explanation nr. 3, life appearing is probable, but life developing these adaptations (via evolution, not random reactions, now that self-replicating life exists) is highly improbable.

Rob Henry September 15, 2011 at 8:09

I think that Avatar has a better case (errors in its details not withstanding) than many here admit, but one thing disturbs me.

There is something very strange about how similar the biochemistry of all life on Earth is. If this was due to necessity it would be understandable, yet there are there are strong hints that there was much flexibility right up to the “last universal common ancestor”.

To mention just a couple of these, both ATP and GTP seem part of LUCA’s compliment of energy buffers, yet they had already become sufficiently specialised to retain their separate function in all extant life. What I’m thinking here is that life at the time of last divergence should have had little reason to use enzymes that were so fine tuned that organisms could only use one of these molecules for a specific process, yet only one variant of their usage pattern survived.

Likewise, of the 23 proteinogenic amino acids used today, LUCA most likely used at least 21, and was reasonably likely to have used 22. Actually, if we believe that the first necessity for proteins to evolve enzymatic function was a code that was likely to provide a protein of sufficient length, it stands to reason that the 22 amino acid set-up (that shows evidence that it would employ 63 out of 64 codons) looks perfect for even earlier forms. If so, one or two of these amino acids has a unique method of incorporation into a protein, and this suggests that there could have once been a much higher level of variability in protein synthesis that was only (largely) standardised around the time of LUCA

Actually there is also a non-ribosomal path to protein production in some extant life, that seems so sophisticated that it is hard to believe that it evolved entirely after standard protein synthesis was well established. This also hints at an earlier and more fundamentally different form of the entire process of that was also very complex.

I have great difficulty in believing that Avatars views on the divergence of life can be so faulty that they can’t become a sort of law when reapplied to the case of variants of one tree of life well before the specialisation levels reflected in LUCA was reached. I know that this sounds mad (and I might retract it after I have slept on it), but I now speculate that either life on Earth did not start here, or it was regrown from a single example after a near-sterilisation event at the end of the late heavy bombardment.

Eniac September 16, 2011 at 2:50

Avatar:

THIS TAKES A LOT OF TIME

Any particular length of time you have in mind?

Following your argument, it seems, we should also observe multiple versions of the genetic code, because surely isolated niches would not by chance evolve the exact same code, and there would not be enough time for one version to replace all others, or would there?

Rob:

I now speculate that either life on Earth did not start here, or it was regrown from a single example after a near-sterilisation event at the end of the late heavy bombardment.

You are free to speculate, but there is no need for such contrived explanations. Single event, yes, quite likely. From space, or during the bombardment, no. Neither of these are necessary or very helpful to explain what we see. Most likely, abiogenesis itself was the single event, either because it is unlikely (my view), or because life spreads quickly and preempts further occurrences (a reasonable alternative view).

I think so far, Avatar and I would agree. However, I also think that even if the above were all wrong and abiogenesis did happen many times, we would still only see one tree of life today, for the reasons I have mentioned. The same reasons that give us only one biochemistry, and only one genetic code. Because, in fact, there was a LOT OF TIME (in Avatar’s capitals) available for the other versions to succumb. About 2-3 billion years.

There were also a billion years between the LHB and the oldest undisputed evidence of life on Earth. Rock formations interpreted as fossilized bacteria, from about 3 billion years ago (see http://en.wikipedia.org/wiki/Evolutionary_history_of_life#Earliest_evidence_for_life_on_Earth for documentation). Considering how difficult it is to be really sure some tiny nodules are fossilized bacteria rather than just unusual minerals, I would give it another billion years, potentially, “undisputed” notwithstanding. Either way, I do not think we need to get all worked up about how “quickly” life arose as soon as it could. Really, there is no compelling reason to think that it did. More likely, it took its time. A billion years, give or take a billion.

Rob Henry September 16, 2011 at 18:22

Eniac, my madness mentioned above was not for the idea of a foreign or late origin of life here, but because I am starting to think that I see clear evidence for it. Finding a universal genetic code is no problem in itself, and might even be expected if we are to believe that the first life to find very high fidelity translation had such an advantage over others that it might replace them. What startles me is that this wasn’t needed as testified by the strong possibility of abnormal selenocysteine (and pyrrolysine?) usage in the LUCA. I’m thinking that this looks like sufficiently high fidelity translation mechanisms were already in usage, and LUCA and its contemporaries were merely in the process transferring these to one standard format. So why did divergence occur at this late state?

Also I love how your late-origin-for-life postulate gives yet more impetus for a palaeontologic investigation of Earth rocks that have been knocked off our surface and landed on the Moon. I hear that there could be 200kg of such terrestrial rocks on every square kilometre of the lunar surface from the late heavy bombardment alone. One day there will be no need to curse the lack of pristine rocks from that era on our modern planet, and you will certainly quickly be proved right or wrong.

Eniac September 16, 2011 at 23:43

Rob, I do not think I understand your first paragraph at all. Nevertheless, let me point out that this “LUCA” is special only in retrospect. In its time, it was just one species amongst many, with no particular distinction. The only thing setting it apart from its contemporaries is that, billions of years later, its lineage would happen to be the only one left. Very analogous to Mitochondrial Eve. LUCA need not even have been particularly fit compared with its contemporaries. As in many sports and card games, pure chance plays just as much a role in winning the extinction/survival game as fitness does.

I consider it likely that at the time of LUCA or before, there was a much wider variety of biochemistry and genetic codes. Life tends to diversify and explore as long as a feature can still be improved, and then settle on one version once further improvement has reached a point of diminishing returns. I speculate that the first ever life was based on only two different nucleotides (most likely G and C), and that A and U where added later. There might also have been other nucleotides that did not make it in the end. Similarly, the genetic code most likely started with just a few amino acids. You can sort of tell which ones they were by examining the code table. Some amino acids look squeezed in on top of the others, presumably they represent the latest innovations. There might even have been a whole branch of early peptidic life where the code was in duplets rather than triplets, later to be beaten out by the triplets because of the wider variety of chemistry available to them.

Anyway, the point is that there could have been just as much diversity among earliest lifeforms as among the so-called “complex” lifeforms of today, it just happened at a different level. The fact that only one of these early forms survives after billions of years has no bearing on that at all, it is to be expected.

@Avatar: Also consider that niches themselves are far from permanent, most come and go quite fast in geological time. This mixes things up, and really limits the LOT of time that you were talking about.

Rob Henry September 17, 2011 at 21:37

Eniac, the possible innovations in early biochemistry that you mention above are in the classic mold, and provide classic killer-advantages of the sort that may lead to replacement of one group by another. What I thought I might have glimpsed is that the contemporaries of LUCA must have had well advanced and equivalently efficient differences.

It could be explained that LUCA’s descendants eventually replaced all its contemporaries in their home habitat, and it could be explained that the community among which LUCA dwelt, was so much more efficient than its contemporaries that it replaced all life in other habitats, but what I’m seeing is the difficulty of explaining how both events coincided without LUCA gaining a sudden advantage. Perhaps what I am missing is that other methods of amino acid incorporation (as evidenced by selenocysteine and pyrrolysine) might have an inherently lower fidelity of placement, its just that the work to prove it has not yet been done/published.

Eniac September 18, 2011 at 21:16

it could be explained that the community among which LUCA dwelt, was so much more efficient than its contemporaries that it replaced all life in other habitats

I was trying to explain that LUCA need not have been more efficient than its contemporaries and still have its descendants replace all other life.

It really helps to grapple with the Mitochondrial Eve concept, it is very analogous, in a much smaller, single-species scope. There were many other women around Eve, and many were stronger and more fertile than she. Her lineage might have expanded and contracted randomly many times in the 200 million years since, as would have the lineages of her contemporaries. One by one, each lineage, by chance, hits the zero point from which there is no coming back (extinction), and only one is eventually left. The time in which this happens is a well-understood function of generation time and population size.

LUCA is a relative concept, an abstract matter of definition. The LUCA we are talking about is the common ancestor of all organisms alive today. If we move “today” back a million years, we would get LUCA’, the common ancestor of all organisms alive a million years ago. This would be a different, earlier organism. It would even be a different (later) organism if we change “alive” to “known to be alive”. You can also define common ancestors for all Eukaryotes (much later than LUCA), vertebrates, or humans (that would be Mitochondrial Eve or Y-chromosomal Adam). There would have been no way to recognize LUCA in its time, no way to predict which of the many critters of that age would make it all the way down the line.

Niches or habitats are not permanent. Lifeforms get replaced in them by invaders all the time, and the habitats themselves are prone to change and disappear. And the best don’t always win. There might have been lifeforms with better chemical or genetic abilities that just happened to draw the short straw because their habitat became uninhabitable (their lake dried out or their undersea vent stopped spewing) before they had a chance to spread out and conquer the world.

ljk September 19, 2011 at 10:19

Status of the UC-Berkeley SETI Efforts

Authors: Eric J. Korpela (1), David P. Anderson (1), Robert Bankay (1), Jeff Cobb (1), Andrew Howard (1), Matt Lebofsky (1), Andrew P.V. Siemion (1), Joshua von Korff (2), Dan Werthimer (1) ((1) University of California, Berkeley (2) Kansas State University)

(Submitted on 16 Aug 2011 (v1), last revised 7 Sep 2011 (this version, v2))

Abstract: We summarize radio and optical SETI programs based at the University of California, Berkeley.

The SEVENDIP optical pulse search looks for ns time scale pulses at visible wavelengths using an automated 30 inch telescope. The ongoing SERENDIP V.v sky survey searches for radio signals at the 300 meter Arecibo Observatory. The currently installed configuration supports 128 million channels over a 200 MHz bandwidth with ~1.6 Hz spectral resolution.

SETI@home uses the desktop computers of volunteers to analyze over 160 TB of data at taken at Arecibo looking for two types of continuous wave signals and two types of pulsed signals. A version to be released this summer adds autocorrelation analysis to look for complex wave forms that have been repeated (and overlayed) after a short delay. SETI@home will soon be processing data of Kepler exoplanet systems collected at the GBT.

The Astropulse project is the first SETI search for $\mu$s time scale dispersed pulses in the radio spectrum. We recently reobserved 114 sky locations where microsecond pulses were detected. This data is in process of being transferred to Berkeley for analysis.

Comments: 8 pages, including 1 figure. Presented at SPIE Conf. 8152, San Diego, CA, Aug 25, 2011

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM); Distributed, Parallel, and Cluster Computing (cs.DC)

Cite as: arXiv:1108.3134v2 [astro-ph.IM]

Submission history

From: Eric J. Korpela [view email]

[v1] Tue, 16 Aug 2011 01:31:30 GMT (448kb)

[v2] Wed, 7 Sep 2011 00:52:44 GMT (449kb)

http://arxiv.org/abs/1108.3134

ljk September 19, 2011 at 10:22

Current and Nascent SETI Instruments

Authors: Andrew P. V. Siemion, Jeff Cobb, Henry Chen, Jim Cordes, Terry Filiba, Griffin Foster, Adam Fries, Andrew Howard, Josh von Korff, Eric Korpela, Matt Lebofsky, Peter L. McMahon, Aaron Parsons, Laura Spitler, Mark Wagner, Dan Werthimer

(Submitted on 6 Sep 2011)

Abstract: Here we describe our ongoing efforts to develop high-performance and sensitive instrumentation for use in the search for extra-terrestrial intelligence (SETI).

These efforts include our recently deployed Search for Extraterrestrial Emissions from Nearby Developed Intelligent Populations Spectrometer (SERENDIP V.v) and two instruments currently under development; the Heterogeneous Radio SETI Spectrometer (HRSS) for SETI observations in the radio spectrum and the Optical SETI Fast Photometer (OSFP) for SETI observations in the optical band.

We will discuss the basic SERENDIP V.v instrument design and initial analysis methodology, along with instrument architectures and observation strategies for OSFP and HRSS. In addition, we will demonstrate how these instruments may be built using low-cost, modular components and programmed and operated by students using common languages, e.g. ANSI C.

Comments: 12 pages, 5 figures, Original version appears as Chapter 2 in “The Proceedings of SETI Sessions at the 2010 Astrobiology Science Conference: Communication with Extraterrestrial Intelligence (CETI),” Douglas A. Vakoch, Editor

Subjects: Instrumentation and Methods for Astrophysics (astro-ph.IM)

Cite as: arXiv:1109.1136v1 [astro-ph.IM]

Submission history

From: Andrew Siemion [view email]

[v1] Tue, 6 Sep 2011 10:33:06 GMT (1340kb)

http://arxiv.org/abs/1109.1136

Rob Henry September 19, 2011 at 23:07

Eniac, you wrote in your last post “LUCA need not have been more efficient than its contemporaries and still have its descendants replace all other life.” You then repeated the intraspecific example of the mitochondrial eve, yet still miss the vital step that Avatar was fixated on.

(Hopefully) none of us argue that that sort of random drift really has its effect, and that nothing can stop it being a powerful force to reduce variation within a single gene pool in a finite population, but when we extend this further we make so many assumptions about extinction and replacement patterns among creatures with very different adaptations (as pointed out by Avatar), that we really need to confirm our models with data from our system, and to that effect I mentioned work publicised by Gould. But one thing that I did not mention was that even within this data, extinction at the phylum level looked problematic, yet with too few examples to tell. Once animal phyla were well established after the Cambrian, there is not a single example of extinction of any such group (that fossilises well).

Your suggestion that LUCA might have differed just a million years ago (or a billion, for that matter) would shake our current understanding of life on Earth and its trichotomy if true. After all, just note how unculturable environmental often come from hitherto unknown phyla, yet, even here, all seem to fit nicely into the trichotomy.

More likely is that just the best reconstruction of LUCA from readily culturable organisms might change over the last, say, 10 million years because of a loss of information. More likely still is that the last eukaryote common ancestor could change over this same 10 million years, but, to me, this just illustrates the problem. If stem group eukaryotes are particularly venerable to extinction it is because they are likely to have to occupy a middle-ground, where if their line further simplifies it would have to compete with other organisms that are already honed in that role, and if they occupy the roles suitable to the most complex organism in an environment they are in direct completion with eukaryote crown groups.

Eukaryotes are finicky and complex organisms with a very low diversity of metabolic inputs compared to archaea and bacteria. It speaks volumes that, despite their plethora of internal metabolic pathways, they have not (to my knowledge) managed to compete with (let alone displace) even one lithotrophic group from the other two branches of life. Even their movement into photosynthetic niches seems only made possible by a one-off symbiosis with cyanobacteria. This fact is particularly surprising in light of the fact that all three groups share a common genetic code, and are susceptible to horizontal genetic transfer.

So it all boils down to the difficulty of determining how easily one very different group can displace all others (that is why I though it necessary to invoke a sudden jump to explain LUCA’s apparent complexity). If you can do that you’re a genius, otherwise, it is thus not too much of a stretch to ponder if Avatar really has a fine point.

Rob Henry September 20, 2011 at 7:44

Above I wrote “none of us argue that that sort of random drift really has its effect” when I meant to write “none of us argue against that sort of random drift really having an effect”. Sorry.

Rob Henry September 20, 2011 at 17:41

Another error with my long comment above is that at the conclusion I forgot to emphasise how the implied sophistication of LUCA was central to my invocation of a sudden jump in innovation within its line. If it lacked this implied level of sophistication there would be far less reason to posit such a jump. After-all that is why I gave examples of how difficult it was for a more sophisticated organism to displace a lesser.

Eniac September 24, 2011 at 0:39

Your suggestion that LUCA might have differed just a million years ago (or a billion, for that matter) would shake our current understanding of life on Earth and its trichotomy if true.

No, the distinction is trivial. Within any arbitrary phylogeny that has a single root, LUCA is simply a definition: The youngest common ancestor of all considered species. Naturally, the phylogenetic node corresponding to this definition depends on what “considered” means. For LUCA, it would be “all currently existing species”. As you go back in time, “currently” changes, and more and more branches of the phylogeny will be included (those that are now extinct), some of which may trace back to one of LUCAs contemporaries. LUCA would then have to be moved back in time. Similarly, if you restrict “considered” to mean “known to exist”, or some other arbitrary subset of current species, you may eliminate the lineages of all but one of LUCAs descendents, making it the new LUCA.

There is no biological significance to any of this, LUCA is just an arbitrary branchpoint in the whole tree of life, but there is no need to postulate any sudden advance at just that time. However, if there were sudden advances at about the right time, LUCA would be more likely to be found near the beginning of the ensuing expansion. So, there may be a correlation, but not a necessity.

It speaks volumes that, despite their plethora of internal metabolic pathways, they have not (to my knowledge) managed to compete with (let alone displace) even one lithotrophic group from the other two branches of life.

How could we possibly know about this? Even if bacterial lithotrophs had fossils, it would be impossible to tell whether they became extinct or not. Over time, almost all species go extinct, so probably they did, but there is no way for us to know if competition from Eukaryotes played role (or not).

Rob Henry September 24, 2011 at 20:46

Eniac, yes, on reflection the distinctions that form the trichotomy do look trivial, in terms of them being amenable to explanation by generation through random growth and pruning, but I believe that the overall pattern of modern groups, and their dominance of specialist environments mitigates against postulating such a random pattern of extinction.

Also of high evidential value here is the extreme antiquity of several modern groups within the cyanobacteria, and for that matter the well known propensity of microfossil species to appear to retain their form over hundreds of millions of years (I know that to outsiders like myself, one microfossil looks rather like another but, apparently, to the specialist this effect is highly significant).

ljk September 24, 2011 at 23:40

SETI Projects Weather Recession – News Blog – SkyandTelescope.com

http://www.skyandtelescope.com

Although funding has eroded for SETI@home and the Allen Telescope Array in the past few years, both alien-hunting projects have survived, thanks to donors and volunteers.

Full article here:

http://www.skyandtelescope.com​/community/skyblog/newsblog/13​0195858.html

Comments on this entry are closed.