Life as Rarity in the Cosmos

by Paul Gilster on April 11, 2008

Although I suspect that intelligent life is rare in the cosmos, I’m playing little more than a hunch. So it’s interesting to see that Andrew Watson (University of East Anglia) has analyzed the chances for intelligence elsewhere in the universe by looking at the challenges life faced as it evolved. Watson believes that it took specific major steps for an intelligent civilization to develop on Earth, one of which, interestingly enough, is language. Identifying which steps are critical is tricky, but in the aggregate they reduce the chance of intelligence elsewhere.

A linguist at heart, I wasn’t surprised with the notion that the introduction of language marks a crucial transition as intelligence develops. But what are the other steps, and how do they feed into the possibility of life elsewhere? These interesting questions relate to how long the biosphere will be tenable for life as we know it. If, as was thought until relatively recently, Earth might support life for another five billion years, we would have emerged early in the history of our biosphere. But it is now believed that in perhaps a billion years, the era of complex macroscopic life will be ending, the victim of decreasing CO2 and increasing temperatures.

Startlingly, we’re faced with the fact that the Earth’s biosphere is even now in its old age. Here’s Watson’s take on the matter:

The question of the future life span of the biosphere has relevance to estimates of the likelihood that complex, perhaps intelligent, life evolves on a given planet. At present, Earth is the only example we have of a planet with life, and the fact that our own existence depends on Earth having developed complexity and intelligence introduces an anthropic “self-selection” bias into our sample of one… If we learned that the planet would be habitable for a set period and if we had evolved early in this period, then even with a sample of one, we might suspect that this suggested evolution from simple to complex and intelligent life was relatively likely to occur. By contrast, however, it is now believed that we evolved late in the habitable period; this suggests that our evolution is a comparatively unlikely occurrence.

The model Watson analyzes assumes that on planets where intelligence arises, its evolution is governed by the need to pass through a number of critical transitions, each of which are unlikely to occur in the time available. Critical steps might be events like the transition from unlinked replicators to chromosomes, or the differentiation of the eukaryotic kingdoms of plants, animals and fungi in the late Proterozoic. A number of essential evolutionary steps are suggested, the common thread being that they all involve increases in structural and genetic complexity.

An alternative to the critical step model would suggest that the evolution of intelligence is simply long and slow. The problem with that idea is our old friend Fermi, whose paradox would force us to ask why we see no signs of intelligent activity around us in the cosmos. For intelligence under the alternative model should have evolved on planets somewhat older than ours, whereas if the critical step model is right, then the passage through the steps becomes a tremendous roadblock to intelligence. The transition from biogenesis to observerhood is tightly constrained.

Why? Back to Watson, who uses the lottery analogy, explaining that each step in the process conditions what follows:

In terms of the lottery analogy, we need to condition our observations on winning not just the lottery of biogenesis, but several subsequent lotteries as well, in which tickets are only issued to those who have won in the previous round. In such a model, the constraint on absolute probability given by an early win in the first round becomes rapidly less useful as further rounds are added.

Is evolution a predictable movement toward intelligence? Watson doubts it:

There are numerous examples where complex traits have apparently been lost from organisms, and the question of whether increases in complexity are in fact any more intrinsically likely than decreases remains unresolved… From the perspective adopted here, this appearance of evolution as a monotonic “progress” toward ourselves results from “anthropic self-selection bias”… In this case, there is no need to postulate any directionality to evolution; and, in general, the kind of outcome seen on Earth may be vanishingly unlikely.

That, of course, has major implications for what we might expect to find around other stars. Vanishingly rare intelligence is the result of the evolutionary lottery taken through its repeated cyclings, and it’s noteworthy that in this model, even where intelligence does arise, it comes late in the history of the planet on which it appears. Thus civilizations find themselves in senescent biospheres, surrounded by other systems that may have some forms of life, but probably not intelligence.

The paper is Watson, “Implications of an Anthropic Model of Evolution for Emergence of Complex Life and Intelligence,” Astrobiology Volume 8, No. 1 (2008).


kurt9 April 11, 2008 at 15:34

The is the evolutionary biology argument for the rarity of intelligence in the galaxy. Personally, I think it carries more weight than the much bandied “Rare Earth” Hypothesis.

tacitus April 11, 2008 at 15:54

Very interesting. We desperately need more than a “sample of one” before we can start turning speculation into something more than educated guesses. Tantalizingly, we’re actually not that far off of at least beginning to get some hard evidence about the abundance of life through the discovery and (eventual) imaging of exoplanets deemed capable of playing host to life.

But I would tend to agree that even if life is commonplace in the cosmos, intelligent life and technological civilizations are rare. There is no special imperative for evolution to push life towards intelligence, even if having intelligence proves to be a great trait to have in the battle of the survival of the fittest.

Adam April 11, 2008 at 16:55

Hi All

I’m yet to read the paper, but one thought occurred to me was that our oxygenic biosphere didn’t emerge until fairly late because of geochemistry. If we date our emergence from the time conditions permitted then we’ve appeared 600 myr after oxygen could build up, and about 1,000 myr before the advanced biosphere goes into terminal decline (cloud effects could delay things somewhat.) By that count it doesn’t seem like intelligence is so late to arise.

Could it have arisen earlier? Mammals date back to ~ 230 mya and their ancestors diverged from other amniotes c. 310 mya. Could intelligent primates have arisen at any point after then? I would suggest we might be running up against the limits of our ignorance of the constraints that channel the flow of evolution. Whether that makes intelligence more or less likely is currently anyone’s guess.

Rob April 11, 2008 at 17:06

I think the term “intelligence” is too broad a brush. We don’t know that high-intelligence directly equates to technology and civilization as an inevitable progression. Once again we only have one example.

What factors lead-higher level intelligences — that manage to remain in balance with their environment (resources, population etc) — to advances in technology and civilization? On our own planet, we might find a somewhat parallel development of different cases within our own species, Europe and the Americas.

In Europe, large population centers would seem to have NEEDED advances in the technologies of resource acquisition and distribution, sanitation, transportation etc in order to continue to exist in their locally “out of balance” environmental state.

North American indians were largely “in balance” with their environments by comparison. Is it not possible then that without intervention an similar entire planetary species — highly intelligent — might continue to remain “undetectable” for thousands of years?

Further, consider the societal factors of other alien cultures may not put such emphasis on the prolonging of life (medical treatment in general), art, science… in forms we recognize. Are these things natural progressions of intelligence or side effects of imbalance.

What then would make an intelligent species — in even more perfect equilibrium with its environment — any more detectable than say, dolphins (presumption of high intelligence there) over thousands of years?

Bob Shaw April 11, 2008 at 19:09

Larry may already have noted these comments, but I hope they bear repeating here.

The thing which renders the Drake Equation almost worthless is the element of time – on the Earth, it seems to have taken billions of years for intelligence to arrive on the scene even after complex life arose (and life itself had been around for a long time before complexity became the norm (assuming that one discounts cryptic subterranean paleobacteria, still chomping rock and which may well outweigh everything else put together!)).

Intelligence is demonstrably rare locally, and rare locally over a lengthy timescale (which suggests that it is rare elsewhere, too, on a ‘snapshot’ survey basis). In any given year, assuming that the Earth is 5 billion years old, and that there has been local intelligence for 5 million years, the chance of intelligence is 1/1000. That’s ‘smart animal’ intelligence, mind you, not civilisation. Writing dates back (for ease of arithmetic) 5,000 years, giving us 1/1,000,000 in any given year. Now, factor in technological civilisation, which has been about for a century or so, and the chance of such a civilisation existing on our own planet in any one year is about 1/50,000,000.

Add in some calculations relating to periods of time civilisations are actively conducting SETI and the numbers get worse – basically, our galaxy is probably full of life, but empty of mind. And there isn’t even a hint of relict astroengineering by past civilisations or AI communities.

And as for ‘mind’ which just doesn’t care to connect with us…

…Drake was just too ambitious.

Bob Shaw

Administrator April 11, 2008 at 21:19

Bob, I suppose we could qualify your “…there isn’t even a hint of relict astroengineering by past civilisations or AI communities” by saying there is no ‘detectable hint’ of such astroengineering at this juncture. As to ‘engineering’ vs. ‘astroengineering,’ there does remain the possibility we’ll eventually find traces of such among civilizations that simply didn’t survive long enough to reach Kardashev Class I, much less II. All that, though, still doesn’t take much away from the weight of what I think is a very powerful argument on Watson’s part, and on yours. The time element is indeed huge.

James M. Essig April 11, 2008 at 21:55

Hi Paul;

Suppose that there is on average one intellegent civilization per spherical volumetric element of our universe with the observable radius of 13.73 billion lightyears. Some models of our universe hold that its spatial extension is infinite thus resulting in an infinite number ETI civilizations.

What would these civilizations look like, what physical form would the ETI take, what psychodynamic structure would their personalities take, etc., is anyones guess.

The idea that living beings with qualitatively completely different psychic structures from the typical intellect, heart, will, and soul of the human spiritual psychology paradimn, or the no longer popular Fruedian psychodynamic theory of the unconcious, subconscious, ego, id and superego, or the more modern nueral network psychophysical theories of human personality etc., really intrigues me. If such beings do not have emotions, what sort of affect to they have. Perhaps such beings have supercharged emotions that might be more refined than our human emotions and affective life. What sort of schemata would their dailly intellectual, cognitive, and perceptual functioning be based on.

One can speculate that their bodies might be composed of organized metastable magnetic fields, electric fields, or electromagnetiic fields. Even if life in our universe is very very rare, the finding of such rarity of life might have some faith based meaning for which we can only speculate as to its significance. A virtually empty universe would allow us a great deal of territory to colonize without the risk of interstellar warfare or unethical treatment of indegionous ETI peoples such as the wrongful takeover of their planetary environment. As we branch out into other stars systems, we will have to be mindful of how we treat any indiginous peoples we meet so that we don’t become the invading ETIs. We may be dealing with this issue in the lifetimes of our great grandchildren; a profound but humbling thought.



kurt9 April 12, 2008 at 0:43

Bob Shaw,

I agree with your numbers with regards to the probability of technological civilizations. I would like to add some more. Your 1/1,000,000 is based on Earth-like planets that have the large moon and the Jupiter in the right orbit around the star. The Jupiter screens out excessive comets and asteroids that would cause impact events. The large moon is responsible mainly for a stable axial tilt that moderates the seasons and temperature variations over long periods of time. What the moon is not needed for is for plate tectonics, because Mars had these and there is no evidence that Mars ever had a large Moon.

Lets say that 1/10 G or K stars have got an Earth in the right orbit. Maybe 1/100 of these has got an Earth with the large moon and the Jupiter in the right place. This makes 1/1000 or 1/10,000 (I’m being charitable here) G and K stars with the right Earth to generate your numbers.

Since our galaxy has maybe 200 billion stars, 7% of these are G’s and k’s, 10% of them in the galactic habitable zone. This means 1.4 billion to 14 billion candidates. Maybe 14 million of these have got the Earth with the large moon and the right Jupiter. Since a civilization occurs only 1 out of 50 million of these, we are alone at least within the local cluster of galaxies. Since the smaller galaxies may well lack the proper metallicity for planets and life and we happen to be in the biggest galaxy this side of the Virgo supercluster, it is likely that the nearest alien intelligences are in the Virgo supercluster, 60 million light years away.

I think the nearest ETI’s, if they exist, are in the Virgo supercluster.

BTW, almost all evolutionary biologists are of the opinion that the evolution of language and tool making intelligence is such an improbable event that it is likely to have happened only once, at least, in our own galaxy.

The universe as a whole is so enormously large (something like a trillion galaxies) that, although I do believe we are alone in our galaxy, there is most certainly ETI elsewhere in the universe. Its just a lot further away than is commonly expected.

How about the saying that goes something like “a long, long time ago in a galaxy far, far away”.

Adam April 12, 2008 at 2:43

Hi All

That issue of “Astrobiology” is currently free online…

…and the paper in question is here…

(PDF format file)

I realised when I looked it up that I had read it briefly when it first appeared a few months back, and it reminded me of Brandon Carter’s very similar paper from the early 1980s. I feel there’s something wrong with the argument, but I have to read further. There seem to be statistical assumptions not being met, but it’s too premature to say more.

Ronald April 12, 2008 at 3:17

I strongly agree with Rob and Bob: the chances ánd window of opportunity for (advanced) intelligence are simply exceedingly rare.

Biological life in general though may be common.

Biocompatible and terraformable planets will most likely be very common, relatively simple chance events.

Some would call this ‘lonely’, I see it as a great opportunity.

devicerandom April 12, 2008 at 4:29

I would like to see clarified if the “senescent biosphere” argument applies only to planets orbiting K or G stars, or if it applies everywhere. That’s why I knew that red dwarfs usually live stable lives for as much as ten times the Sun -so, taking into account only star evolution, a biosphere could conceivably sustain itself for tens of billion years.

In that case however it comes to mind that the planet would undoubtly get old itself -plate tectonics probably grinding to a halt after, say, 10 billion years? -what would be the consequences of that on the biosphere?

Afonso April 12, 2008 at 6:14

But even in the case of very rare inteligence, all that is needed (to have Fermi’s paradox) is that a single instance (of a technological civilization) has won the ultimate lottery (surviving it’s mother star death).
I believe that, from a certain point (very early rather than very late), evolution is soo exponentialy fast (comparing to the time scales of interstellar comunication/travel) that this same comunication/travel becomes pointless.
This is what the transhumanists call the post-singularity reorientation towards the inner/micro universe.

george scaglione April 12, 2008 at 9:02

hello all i read recently lol i think here that we may indeed be alone in our galaxy but that the virgo cluster might be a good bet for intelligent civilizations just based on the number of stars there.but if space is infinite as some say today,and in all probability it is…then there would indeed be a great many intelligent species out there! kinda make it necessary to have traversable wormholes though.just try to imagine the distances!!!!! thank you very much george

philw1776 April 12, 2008 at 11:43

This evolutionary biology arguement for the paucity of technical civilizations can be even taken further. Today we have not a clue how the first replicating biologicals occured. What if that itself was a once in a universe event? Using the same reasoning that the evolutionary biologists use, I think not. Life began so early in the Earth’s existence that we have a hint that its occurance might be readily achieved. If we accept this arguement for the prevalance of life, then to be consistent we must accept that complex ‘animal’ life only arose late, in the last quartile of the Earth’s existance. Not a good outlook for one of very many chancy steps needed afterwards toward the emergence of technical civilizations, especially considering forecasts from some climatoligists that solar evolution luminosity gain will render the Earth inhabitable in just 3-4 hundred million more years. If this forecast is true, Earth’s complex life forms just made it in the brief time window of habitability surrounding a G star.

Malcolm April 12, 2008 at 12:19


“…Jupiter screens out excessive comets and asteroids that would cause impact events”

…or maybe it doesn’t;

I think we’re still trying too hard to extrapolate from a sample size of one here; until we have more data we’re all just guessing. The jury is still a long way from reaching a verdict on the Rare Earth theory; some of its assumptions, such as Jupiter as an impact shield and the Galactic Habitable Zone ( are starting to look shaky.

Of course, this may well all be prejudice on my part; I **want** there to be lots of intelligent life in the galaxy/universe, and am therefore predisposed to dislike the Rare Earth. I may very well be wrong about this; after all, I’ve been wrong before, and it’s **just** possible that I could be wrong again… ;)

Whatever the case, as the late great Sir Arthur said: “Sometimes I think we’re alone in the universe, and sometimes I think we’re not. In either case, the idea is quite staggering.”

Athena April 12, 2008 at 14:57

I skimmed the Watson paper, and I have a few thoughts. By the article title and his remarks in the Conclusion section, he places himself on the anthropic/rare earth side of the issue.

The early-versus-late biogenesis argument cannot be easily settled with models, nor is it a given that each critical step occurred at evenly spaced intervals. Evolution creates branchings, and change rates differ in organisms, depending on their generational times. Additionally, the question of evolution directionality is irrelevant to his argument. Finally, his transition stages between 6 and 7 omit quite a bit, in the interests of (perhaps artificially?) emphasizing the time gap.

Interestingly, the crucial shift in hominids may not have been language but music, coupled with bipedalism. Check out Steven Mithen’s fascinating book on the subject, The Singing Neanderthals: The Origins of Music, Language, Mind, and Body.

Intelligence doesn’t equal technology. Observable signals, yes. Intelligence, even sophisticated culture, no. And models are only beautiful constructs, until validated by experiments and/or observations. Physicists and biologists know this well — so should astrobiologists.

Zen Blade April 12, 2008 at 14:59

With regards to the chance of life occurring, if we assume that the RNA World Hypothesis is correct, or is at least partially accurate, we must remember that life went through some stage where ribonucleic acids (and perhaps something else prior to that) were the genetic and catalytic material of choice for pre-DNA organisms.. (there are other related/complementary Hypotheses as well).

The issue with the RNA world, is that you can only make your nucleic acid chain so long before you literally run out of material, from a sampling perspective. If we assume 4 choices for any one position (A,C,G or U), then in order to sample all possible sequences of a 20 nucleotide (nt) long chain, you would need enough material for 1,100,000,000,000 different sequences. The smallest ribozymes (RNA enzymes) I can think of (off the top of my head) are around 40 nts long.

This being said, life appears to have developed fairly quickly–perhaps indicating that there are numerous solutions to how early life can develop. Or, that at least here on Earth a solution was found fairly quickly–be it luck or otherwise.

skipping forward somewhat in the timeline….
As we learn more about the different domains of life, we have found that many “critical” events appear to happen rather commonly, and this will likely only continue to be the case as we learn more about the numerous microorganisms that we can not see with the naked eye. I think this pattern can be applied for most, if not all, adaptable traits (is intelligence or tool-making an adapted trait?). Be it camouflage, horns, tool-making, etc…

I remember a couple weeks back while discussing consciousness, a few of us spoke briefly about communication and how language might relate to consciousness… I think this is a very important concept. I would not be surprised if the key developmental trait was our outward desire to communicate, not just with people we know, or with strangers, but everything and anything we see… animals, plants, cars, trees… figuring out how to communicate requires puzzle-solving abilities—-I wonder where the current research on this topic is.
–Are there other species that try to communicate so regularly?

Regarding tool-making, this ability can be found throughout nature. Numerous species use tools and construct tools. THIS HAS BEEN OBSERVED AND RECORDED BOTH IN NATURAL ENVIRONMENTS AND CAPTIVITY.
Primates, Dolphins, Crows, to name some of the most obvious (and recently documented) examples amongst species that are considered “intelligent”.
I don’t know what the current status is on elephants, but I would not be surprised if they could also be included within this cluster.

I am more of a fan that intelligence, or at least the biological components that allow for intelligence take a long time to develop. And these components are not necessarily going to happen, but given enough time the components become more and more likely to appear. Eventually, if those components are present, intelligence can emerge.

We humans have only been “intelligent” for a little while. Had we not pushed forward, I think another species on Earth probably would have (in a few million years, give or take). Perhaps there were some very important steps taken 500 million years ago that allowed our neuronal systems to take on properties that would nurture “intelligence”, who knows… but I would be inclined to believe that “intelligence” is really only one piece of the puzzle to how/why man developed technology.

I would also be inclined to believe that evolution has shown that frequently there are numerous ways to reach an acceptable solution. I wouldn’t be surprised if this fact held true for ETI’s.

Sorry if my comment jumped around too much.
-Zen Blade

dad2059 April 12, 2008 at 15:25

Alfonso makes a good point, it takes only one species in a particular galaxy to survive their mother stars’ death to transcend into an artificial or natural multiverse.

I believe I read somewhere that this galaxy isn’t that much younger than the Universe itself, 9 billion years old I believe. With our star and solar system at 4.5 billion years, that leaves a previous 4.5 billion for a race before us to exist. If they existed at all, one would assume they would’ve saturated the galaxy with their type, self destructed or transcended into a self created universe.

I don’t know what form a ‘transcension fossil’ (John Smart) would take, but after searching for bracewell probes, looking for them might not be a bad idea.

Steve April 12, 2008 at 17:02

I have said it before in length, but I will again in brief. I think we all are a litlle too sure we would recognize “intelligence” if we saw it. We again, have but our own “sample” to look at. I am not at *all* sure we could identify a “Super Civilization” even if there was evidence of it all aroud us.

I think intelligence in many forms, civilizations, and otherwise, may be fairly common in the Universe, but in a sense invisible to us because of sense limitations and our own Anthropomorphic Blindness.

Thanks. My 2 cents.


Zen Blade April 12, 2008 at 17:32

I just had a chance to look over the paper that inspired this thread, I have a few critiques….

1. Timeline. I am not in an Evolutionary Biology department, but I have a few friends who are. I’ll ask them next time I see them, but I recall one or more of them saying that the oldest evidence for life was around 3.5 gya. HOWEVER, I recall the person also saying that the evidence was fairly weak until something like 2.5gya… The comparison I remember was comparing what was found from the Martian meteorite 5-10 years ago. Basically, the evidence for some of the earliest life is (or at least was) rather thin because although the evidence could have come from life, it could have also been made by something else.

2. Lack of empirical evidence/empirical references. There has been a lot of information generated regarding phylogeny and the evolution of the various kingdoms/domains of life (the somewhat recent 6 kingdoms or 3 domains is somewhat outdated now). I was disappointed that the findings from these studies were not used or incorporated more fully into the paper.–This is particularly relevant for “transitions 4,5,6″.

3. Some of the transitions… are very speculative. Sexual reproduction for example. Yes, most single-celled organisms don’t have sex, but lateral gene transfer definitely happens… and actually brings up a very interesting point about what is a bacterial “species”. Cell differentiation… multicellular organisms were definitely a big “step forward”, but single-celled organisms can act as a larger organism to create spores and other structures through communicating with their neighboring organisms. These cues are very important. What was the trigger that led to multicellular organisms, don’t know.

4. Assuming transition X is essential for Trait Y… Each of these transitions must be both a) difficult/rare and b) critical for the development of intelligence. Taking into account all of the different organisms on earth, we are really only looking at a very small subset of the entire set of organisms on this planet… and the transitions being selected are only intelligent guesses (at best). More time should have been dedicated to justifying these transitions.

5. Something only evolving once… A couple thoughts: First, just because we haven’t found evidence for multiple evolutions of said trait, doesn’t mean it hasn’t happened. Second, if some trait TRULY confers a dramatic advantage in a certain environment, then it is unlikely that other later organisms would develop the same trait since that environmental niche is already filled. It is more likely that a different trait that allows invasion would be developed. –This being said, many traits are developed, lost, regained, etc… But, if we are talking about absolutely critical traits, one would imagine that these traits would be less likely to be lost, and would be more likely to allow proliferation of said organism…

If the point of the article is to say, it took x year for man to evolve, that’s fine, but to say that it had to go through a set number of unlikely steps… that is overreaching, IMH Biochemist Opinion.

-Zen Blade

Bob Shaw April 12, 2008 at 19:18

As I’ve commented previously, the real key to SETI is Deep Time; by looking across a range of past epochs we may detect the signatures of past civilisations, be they signals or evidence of physical changes to galaxies. In that regard, optical astronomy probably offers the best hope of discovering anomalies which indicate intellect. Although civilisations may not endure for all sorts of reasons, their residues should – perhaps only as such things as enhanced metallicities in the spectra of early galaxies. Subtle traces in themselves are nothing, but once enough Deep Time is trawled then the patterns should become obvious.

There is, however, no obvious way to detect non-technological civilisations, which might well outnumber our own variety many times over. Equally, there may be technological civilisations which have turned inward and have no particular interest in communication (though I suspect that sufficient hobbyists/prosletisers/humourists/teasers would exist in such circumstances to allow for some evidence to leak out).

Humanity is close to having the technological ability to image terrestrial worlds around nearby stars, and I am sure that evidence of life will be detected as well – but that it will be methane-burping microorganisms. Us guys, sadly, are rare.

Bob Shaw

Adam April 13, 2008 at 5:18

Hi Zen Blade

Excellent posts – the “jumping around” was still relevant as the theoretical basis of Watson’s argument is the major transitions theory of Eos Szathmary and Maynard Smith, of which you covered several. Central to their theory was that each transition involved a change in information communication and storage in living systems.

You also said…

I am more of a fan that intelligence, or at least the biological components that allow for intelligence take a long time to develop. And these components are not necessarily going to happen, but given enough time the components become more and more likely to appear. Eventually, if those components are present, intelligence can emerge.

…and that’s my take on the processes involved too. All the transitions arose when the conditions were right, for long enough.

One thing in Watson’s paper is this little discussion of intelligence as just one possible unique trait amongst many other traits in other lineages…

It is worth emphasizing that, while I have focused
on the set of steps that leads to intelligence,
this is in a sense an arbitrary choice dictated by
our special interest in this defining property of
humans. The critical step model is quite general
and could be applied to any other set of steps. For
example, suppose we were interested in the evolution
of elephant-like animals and considered
the possession of a trunk as the most important
attribute an organism could have. Suppose further,
that the evolution of a trunk requires one
unlikely step beyond those required for the evolution
of complex animals. The model could then
be used to predict the probability distribution for
the time of appearance of animals with trunks
within the set of all planets on which such animals
evolve. As it happens, this would be identical
to the distribution for intelligent observers
within their set of planets, as has been discussed,
since they appear to require the same number of
critical steps.

Ref: Watson, A.J. (2008) ASTROBIOLOGY, Volume 8, Number 1, 2008 pp.175-185.

This reminds me of arguments against the evolution of traits via mutation, but neglecting selection. Imagine 500 mutations separate two species and each mutation occurs once in every 10 million organisms. To jump from one species to another in one macromutational jump is (10^-7)^500, which is clearly absurd. Takes about 10^3500 organisms, some 10^3493 generations, before a organism with all 500 is likely.

But each mutation is advantageous and thus preserved in the populace once it appears. If the advantage is ~ 1% then the individuals with a mutation dominate the population in about ~ 100 generations (geneticists please correct me), thus about 50,000 generations are needed to produce organisms with all 500 mutations. That’s the power of selection. But individual end-points of that process would seem incredibly unlikely – and they are – but it happens anyway. Selection extracts “signal” of advantage from the “noise” of mutation pretty effectively, considering the alternative.

ljk April 13, 2008 at 8:14

From the 1997 film version of Contact:

Young Ellie Arroway: Dad, do you think there’s people on other planets?

Ted Arroway: I don’t know, Sparks. But I guess I’d say if it is just us…
seems like an awful waste of space.

Ronald April 13, 2008 at 9:31

@Kurt9, not too gloomy ;-) , one may not need to go as far as the Virgo cluster (the Virgo *super*cluster we are part of): the Andromeda galaxy is quite large and seems to have a larger fraction of main sequence and solar type stars. So our nearest ETI may only be about 2.5-3 million lightyears away ;-)
Furthermore, as Malcolm also mentions, the Jupiter screen function is questionable, beside the fact that Jupiter type planets appear to be quite common.
And even a large moon is mainly something that we ‘are used to’, not an absolute prerequisite.
Finally, (late G and) K stars can have lifespans of tens of billions of years, making advanced life, if and when it arrives at earthlike timing, not appearing so late after all.

@Adam: I think your latest posting says it all: life in general is NOT, never, a matter of sheer coincidence, but a combination of certain biochemical ‘driving mechanisms’ and natural selection. For that same reason complex macromolecules exist, even with self-organizing and self-replicating traits, that could otherwise not exist from a purely chance-event point of view.

kurt9 April 13, 2008 at 13:43


I read somewhere that the Andromeda galaxy, although bigger in size than ours, is actually less dense and, therefor, has fewer stars than our own. Also, the average metallicity of its stars is lower than ours.

Otherwise, I would agree with you. I read “The Anthropic Principle” in the late 80′s. From that point on, I always assumed that the nearest aliens would be in Andromeda. Now I thinks its Virgo.

You know, the cheezy 80′s movie “E.T.” was not too far off with its estimate about ET coming from a place “3 million light years away”.

Technically, you’re right that we are part of the Virgo supercluster. However, we are way on the outer fringes of it in kind of the same way that Barstow California is a part of Southern California. The main part of the supercluster is 60 million light years from year.

The Virgo is not even the largest collection of galaxies. There are several larger colections (5-10x larger) 200-300 million light years away.

In short, I believe that ET exist, but that they are a lot further way than most people presume.

bchurch April 13, 2008 at 15:42

The focus of comments seems to be on mental aspects of evolution, i.e intelligence, but I wonder if our transition to civilization hasn’t been due in equal part to physical characteristics like opposable digits. The ability to manipulate tools doesn’t do much without intelligence, but neither does intelligence do much to advance a species towards civilization without an ability to manipulate the environment through tools.

So while some sort of higher intelligence may be a valuable evolutionary trait, it seems as though it would usually come into play long after certain physical plateaus have been reached. For example, by the time dolphins evolved any significant intelligence, it was too late for them to physically evolve to sorts of arms/hands/digits that would allow them to use that intelligence to manipulate the environment– their fins are already too specialized to evolve backwards into something that could then be evolved into a useful means of interacting with the enviornment (in the way hands are).

One big stroke of human (or primate) luck may be that we had such physical equipment already evolved for swinging around in trees. It just so happens that this equipment translates very very well into tool manipulation when combined with intelligence. But how many other sorts of species could be so lucky? Maybe an elephant’s trunk could serve as a decent starting point– but there’s only one of it, and the lack of skeletal support makes finer motor skills difficult. Tentacles would be better, but their usefulness on land is questionable, and it seems at first blush that elemental expliotation required for andvanced civilization would be more problematic in water than on land.

Adam April 13, 2008 at 19:07

Hi bchurch

Good comments.

I think it was Engels who first pointed out that evolution of hominids first meant bipedalism to free up the hands from locomotion. Seems like a logical move for a future tool-wielder. Birds are bipeds, but missing the extra set of limbs. Could hexapods have evolved flight and digital manipulators? Could the pterosaur single wing-digit approach have led to useful hands?

On other worlds there’s no reason we know why such alternatives could not have arisen. So perhaps we are being too prosaic in our thinking?

bchurch April 13, 2008 at 22:38

Interesting ideas, Adam. I’m sure there’s a whole myriad of limbs that could serve the same purpose as our arms hands and fingers, even if I lack the imagination to come up with them.

As for hexapods, there don’t seems to be any instances of it working here on earth– all animals large enough to support a complex nervous system seem to have been stuck with four limbs (even if all are not necessarily quadrapeds). I’ll confess I don’t know whether this is believed to have resulted from a single common four legged ancestor or whether it four leggedness evolved multiple independent times. It could be that once an animal reaches a certain size, the utility of extra limbs doesn’t match the cost in resources; four seems a pretty stable number for moving around and balancing on land.

One part of me wants to imagine that life could have evolved into something far different on another world, but another part of me thinks that there are probably some basic commonalities that have more to do with efficiency and material physical limitations than any unique environmental constraint on Earth or mere chance. I tend to actually lean more towards the idea that the same sorts of broad features would evolve pretty regularly in independent cases, even on different worlds. Whether large animals having four limbs is one of those features, I don’t know.

Interesting that you brought up pterodactyls, I hadn’t considered that. But I guess the closest we’ve seen in the past to an animal with anything resembling arms/hands would be bipedal dinosaurs. Assuming that they’d lived a few hundred million years longer, could some of them hit the double jackpot of more dexterity in their upper limbs and intelligence?

Ronald April 14, 2008 at 4:35

as for the nearest ETI in Virgo, you may be entirely right, I simply have no idea (who has?).

Andromeda (M31): the latest I read is that, although indeed, its mass seems to be somewhat less than that of our Miky Way (but that may appear to be within margins of error), that is probably largely due to a smaller dark matter mass and its number of ‘normal’ stars is actually significantly higher than the MW’s: I read estimates of varying from 400-1000 billion, more recent ones tending towards the higher end.
Metallicity seems to be generally OK as well (well, there are old metal-poor star clusters in it as well, but that does not seem to be the general picture).
See for instance ‘The Milky Way versus M31, by Tim Hunter’ with its references. Even the halo is relatively metal-rich.
Aren’t you confusing Andromeda with the Maghelanic dwarf galaxies, which are metal-poor indeed?
Also some interesting info and refs on Wikipedia.
Quotes: ‘(…) recent observations by the Spitzer Space Telescope revealed that M31 contains one trillion (1012) stars, greatly exceeding the number of stars in our own galaxy’; ‘M31 does contain many more stars than our own galaxy and has a much larger size. In particular, M31 appears to have significantly more common stars than the Milky Way, and the estimated luminosity of M31 is double that of our own galaxy’. But it also adds that star formation is (3-5 times) greater in our MW, so that in the (distant) future we may catch up with M31.
So do not discard Andromeda and our Local Group yet. Then there is also M33, Triangulum galaxy, in our Local Group, though I know virtually nothing about it.

To quote the late great Sir Arthur: ‘I am just a smalltown boy, hardly interested in anything beyond the Milky Way galaxy’.

Though I would like to add: I will make an exception for Andromeda, my favorite galaxy beyond our own (and it is important to maintain good relationships with the neighbors ;-) ).

kurt9 April 14, 2008 at 13:16

Hello Ronald,

I did some reading about Andromeda. As far as we know, it does indeed have more stars than our own galaxy does, although it is less massive. So, it may be possible that the nearest ETIs are a mere 2.3 million light years away.

There are about 5-6 galaxies closer to us than Virgo that are larger than our own. One would think that these are likely places for ETI. However, unless they do any kind of galactic level engineering works, we are unlikely to detect them. Any kind of radio transmissions from these great distances are likely to be so weak (inverse square law attenuation) that they are unlikely to be distinguishable from background noise. I think that even Dyson spheres and the like would be difficult to detect at the distances that these galaxies lie at (2.3 million lyr for Andromeda, 15-20 million lyr for the others).

Unless a very fast FTL or transversable wormhole technology gets developed, we are alone for all practical purposes.

Adam April 14, 2008 at 15:14

Hi All

Andromeda is ~ 2.5 Mly away according to the most recent estimates, though some go as high as 2.9 Mly, the figure in most studies is 785 kpc (2.56 Mly.) Interestingly, according to Frank Tipler, a Hypernova in M31 is the most likely cause of the “Star of Bethlehem” phenomenon in the New Testament.

bchurch, I’ve always found the idea of intelligent dinosaurs a real possibility as they’re the closest group to birds that still retained useful hands. Contrary to their bad press some dinosaurs had large brains and, as we know from crows and Homo floresiensis, a big brain isn’t always a sure sign of tool-using ability. Ken Macleod, the Scottish SF writer, wrote a trilogy (“Engines of Light”) which posited bipedal dinosaurs as “the Greys” of UFO-folklore – his ideas are well worth exploring, as he did a bit of research developing his concepts. He also drew on materials from Chris Boyce, the late SETI researcher, about ETIs in the Kuiper Belt/Oort Cloud.

Zen Blade April 14, 2008 at 17:02


Regarding limbs, think common ancestor. Pretty much all/most of the 4-limbed organisms you can think of had a common ancestor 400-500 million years ago (although I could be off by several hundred million years). Some organisms (snakes) have lost limbs, and they could definitely regain their limbs–dependent on what exactly happened to their genome to get rid of the limbs in the first place. The bigger question is how long does it take for this trait to come and/or go. Many marine animals have different… “limbs” and I believe they have been aquatic for 50 million years or fewer… That could give us a sense of how long it takes to lose limbs–especially if we have fossils detailing different stages of the evolution.

Insects have 6 limbs, spiders 8 limbs, other organisms have other numbers, but it is completely dependent on where/who you came from. You aren’t spontaneously going to generate new limbs if something is already working. It’s possible that mutation could give rise to additional appendages, but this is more likely going to occur gradually than “poof, now our species has four arms”.

Some of these linkages are still being worked out, but I bet you could find some information somewhere linking the different gains/losses of limbs online.

-Zen Blade

yeti April 15, 2008 at 6:30

i agree with the comments that say we need more than a sample size of one but intelligent life is looking rare.

technological intelligence does not appear to be a convergent feature of evolution. We can see this becuase the experiments have already been done over hundreds of millions of years on earth . Africa,south america , newzealand etc land masses seperated for hundreds of millions of years but only on one, Africa, did technological intelligence arise

when humans went to new zealand we didnt find any animal occupying the human niche despite the fact those animals had 200 million years to evolve tech intelligence which is ALOT longer than the 3 million years it took our brains to treble in size in africa. So even with collosal timespans tech intelligence is not inevitable. Same with south america no intelligence despite having the “raw materials” & plenty of time.

i think this tells us tech intelligence is extremely rare.

Zen Blade April 15, 2008 at 14:16


the problem with what you wrote is that, we humans could simply be the first. We could be the leading edge. There could be other species heading in that direction, but they won’t reach it for some time. And realistically, we didn’t separate from many of the organisms in Australia until ~180 million years ago. Enough time to diverge, but enough time to independently develop intelligence leading towards technology?

Just because something hasn’t happened, doesn’t mean it can’t or won’t. It just means it hasn’t happened… yet. The converse is also true, just because something did happen does not mean that it will always happen, it just means that it has.

I point this out because, what if intelligence had developed on Australia 5 million years ago, before humans or human ancestors began to behave “intelligently”?

And there do exists crows near Australia that make and use tools… and dolphins.

-Zen Blade

david lewis April 15, 2008 at 18:26

There are elephants that have learned how to paint. If their trunks are flexible enough for that then adaptations that might enable them to be versatile tool makers might not be that improbable. However is there a need, any evolutionary pressure, for such adaptations? Given the need, and a few million years, they might make the leap to a technological civilization. However there might also be evolutionary pressure that counters such adaptations.

I recall one of the sites linked to by this site a while back,, that dealt with oxygen in the oceans. If this is common then the steps for complex life to appear might go like this:
- a billion years for life to appear
- two billion for complex life to appear
- several hundred million for intelligent life to appear.

A planet might then need, at minimum, 3.5 billion years for intelligence to appear. (Combine this with the post above “Massive Gamma Ray Burst Still Lingers” and one wonders if within this galaxy our arrival on the scene might be the earliest one can expect intelligence to appear.)

3.5 billion years is a long time. What size would a planet need to be to retain its atmosphere and have plate tectonics for this length of time I wonder. The planets more likely to possess both of those for a long period of time would be larger and hence be ocean worlds where intelligence might arise, but never become technological. Larger worlds would also have more protection against impacts.

If we ever venture forth into the galaxy we might find:
- many worlds smaller than the earth where conditions suitable for life did not last long enough for an oxygen atmosphere to emerge.
- many worlds larger than the earth where life did arise and evolve intelligence but never a technological civilization due to the ocean environment.
- a very few worlds where conditions are not to dissimilar to that of earth.

The universe might be filled with intelligences, we might just need to actually go to them first in order to be able to speak with them.

Though I wonder if intelligent life has actually evolved on earth yet. Are we intelligent? We’re pretty clever technologically yet we, as a race and as individuals, do things that are not intelligent. Nuclear arms for one. The mere fact that we can consider creating artificial plagues. A true intelligent species would not hesitate once it has the ability to create a meteor defense for its sole place of habitation yet we have few people who would support such things and more who would rather we abandon technology altogether and go back to nature. What is intelligence? What might another species define intelligence as, and would we meet their definition.

yeti April 17, 2008 at 8:32

Zen blade its a fair comment to say “we dont know” but i also think its wishfull thinking on your part.

from what we do know i think its pretty safe to say tech intelligence is not a convergent feature of evolution. if we had found another species occupying the intelligence niche on these other continents then the arguement would be reversed we could say tech intelligence is a convergent feature of evolution. and it should be common in our galaxy. unfortunately it deosnt match what we see on our only data point for life in the universe.

we’re looking for a very specific kind of intelligence, a species specific kind. Dollos law shows us that any particular species specific trait , like human intelligence, once it disapears never re-appears in the fossil record.

i dont think we would ever have another tech intelligence on earth again if humans were wiped out.

andy April 17, 2008 at 15:40

There’s some interesting abstracts from AbSciCon 08 which may relate to the evolution of intelligence, particularly this set, which contains “Inferences from the Independent, Infrequent, and Underutilized Evolution of Intelligence on Earth” and “The Planet of the Apes Hypothesis and Why Human-Like Intelligence Is Not a Convergent Feature of Evolution”.

One of the best arguments against “runaway technological intelligence” being common is that cephalopods evolved about 500 million years ago. Since cephalopods are among the more intelligent creatures on the planet, intelligent life may have existed for half a billion years on this planet without developing a technological civilisation.

The other sobering thought is that technological growth may well become self-limiting (so much for the Singularity!): that would provide another possibile explanation for the Fermi paradox.

Zen Blade April 17, 2008 at 16:26


I think you are over simplifying things.

1. Intelligence on other continents.

Your supposition would be correct if we had stayed on Africa in an intelligent state for millions, and millions of years. “We” did not. “We” migrated and were present on much of Europe and Asia for the past 1-2 million years. “We” = closely related hominids.

Homo Sapiens took off less than 200,000 years ago and were on 6 of the continents by 10,000 years ago. The point being that we have expanded very quickly and rapidly. During that expansion we have contributed to numerous extinctions of species across the globe.

Thus, using the single example we have… only 1 intelligent species can exist at a time because that one species will quickly come to dominate the entire planet before a second species can evolve intelligence. –This is quite a leap in speculation on my part, but it is just as plausible as your hypothesis.

Thus, we would not have expected to find the intelligence niche developed on other continents because if it had done so first, it would have marched over Africa and likely stopped our intelligence progression. [again, speculation]

2. Regarding, “once it disappears [it] never re-appears in the fossil record”… that’s just not accurate. Some traits to reappear. Their is genetic evidence that some species of insects have gained and lost the ability to fly several times do to adaptation to new environments. I don’t know how thorough this area of research has been, but unlikely is different from impossible. It may be unlikely to re-evolve a trait, but not impossible. For example, whales, dolphins, marine mammals, they all came from a land-based mammal. They re-evolved the ability to live in water (fins can be the specific trait).

Again though, the problem lies with trying to make definitive statements using too little data. Scientists often use “suggest” or “likely” or “possible” because it is very difficult to make a declarative statement that has no possible interpretation.

-Zen Blade

Zen Blade April 17, 2008 at 18:38


I’ll take a look at those abstracts when I have a chance tonight, but regarding Cephalopods,

The problem with comparing cephalopods is that the whole nervous system is distinct from that of mammals. We are comparing apples and oranges, and it isn’t clear how you can get apple cider from oranges… or if you can, how long it takes.
I say this because there are certain physical developments/traits that must be present for higher intelligence to develop. The invertebrate route of evolution may not favor some/all of those traits. That doesn’t mean those traits won’t develop, just that those traits may be less likely or that they may require different/longer routes.

-Zen Blade

andy April 18, 2008 at 5:57

The problem with comparing cephalopods is that the whole nervous system is distinct from that of mammals.

In the discussion of the evolutionary convergence of technological intelligence, that is surely an advantage: if technological intelligence is a convergent feature of evolution, then a totally different route to intelligence should converge to the same type of intelligence. Cephalopods have had 500 million years and have not.

The chance of mammals evolving on an alien planet is essentially zero, so if a mammalian nervous system is required for technological intelligence, we can safely say that we are the only technological intelligence anywhere.

yeti April 18, 2008 at 12:51

zen im sorry it was really bad wording on my part i should say- Once a species goes extinct it never re-appears in the fossil record or never re-evolves.

our intelligence is unique – making it species specific. Its like a dodo bird saying “i think dodo birds are common throughout the galaxy”.

i wish there was evidnce that tech intelligence is a convergent feature of evolution. But its just not there.

David Nataf April 21, 2008 at 11:05

Dolphins, humans and parrots are each on very different evolutionary tracks, and each has developed language. As such the development of language cannot be argued to be a “vanishingly” rare event.

Personally I’m not interested in such papers because they are non-scientific. So it took 3 billion years on earth to go from the first life to intelligent life… is that fast, slow or average? The truth is that nobody has an educated opinion on the matter.

I’ll also note that Watson eagerly states that the Earth will no longer be habitable a billion years from now. Perhaps not, but K stars live many times longer than G stars like the sun, and they’re a lot more common.

Lastly, it should be noted that Andrew Watson has an agenda. He’s involved with the Gaia hypothesis, and it’s not exceedingly rare for some environmentalists to be opposed to space romanticism. They sometimes fear the prospect that it could lower our valueing of the Earth.

ljk April 22, 2008 at 9:18

Where might we find alien life in the Milky Way galaxy?

At the Astrobiology Science Conference 2008 in Santa Clara,
Charley Lineweaver, a Senior Fellow at the Planetary Science
Institute, contemplated a “galactic habitable zone”:

Ron S April 22, 2008 at 13:43

I did skim Watson’s paper when this thread was new, and stopped because I got annoyed with his faulty analysis. I think this blog entry (link below) does a nice, succinct job of demolishing Watson’s faulty statistical analysis. He suffers from the too-common defect of assigning arbitrary priors.

ljk April 28, 2008 at 22:47

Nick Bostrom hopes SETI never succeeds:

ljk May 1, 2008 at 12:50

The Astrobiology Universe

The Astrobiology Science Conference, recently held in
Santa Clara, California, was a complex universe teeming
with topics and ideas. Although there were far too many
interesting presentations to cover in full, this overview
provides a few highlights.

ljk May 23, 2008 at 13:10

Sun’s properties not ‘fine-tuned’ for life

New Scientist news service May 22, 2008

There’s nothing special about the
Sun that makes it more likely than
other stars to host life, a new
study by Australian National
University scientists shows. The
finding adds weight to the idea that
alien life should be common
throughout the universe. They
suggest that there are probably no
special attributes that a star
requires to have a…

ljk April 16, 2009 at 18:41

Universe May Not Be “Fine-Tuned” for Life

The chemistry of life may be more robust than we thought against changes in the fundamental laws of physics.

Wednesday, April 15, 2009

The anthropic principle is the idea that the physical laws that govern our Universe are precisely those that allow complex life like ours to emerge.

Many scientists have wondered at the balance of these laws, arguing that any small change would alter the universe so radically that life would be impossible. Why is the Universe so finely tuned for life, they ask.

Nobody has come up with a reasonable answer to this question but today James MacDonald and Dermott Mullan at the University of Delaware argue that matters may be more robust than we thought.

Their argument is about the strong nuclear force. Various physicists have noted that if the strong force were just a little stronger, then protons would bind together more readily. That would mean that soon after the Big Bang, most protons would join together to form diprotons, leaving few if any single protons available to form hydrogen. Consequently, chemistry as we know it would be impossible.

But this reasoning fails to take other factors into account, say MacDonald and Mullan. The biggest factor is that protons and neutrons will always bind more strongly than protons and protons, regardless of the strength of the strong force. So although diprotons would form in this universe, they would also tend to decay into deuterons.

So hydrogen (and deuterium) chemistry would be just as likely in a Universe in which the strong force were stronger. (Of course, how the change would affect the the nucleosynthesis of other elements is another question.)

The work gives the lie to some of the more extraordinary claims regarding the anthropic principle. For example, some argue that since we are unable to find anything special about the combination of laws in our Universe, then maybe any permutation is possible. And if any permutation is possible, then perhaps these combinations exist in countless other universes. Of course, the only one we would experience is the one in which the laws are fine-tuned for our existence.

That’s an extraordinary line of argument. But the alternative–that organic chemistry is an emergent property of a wide range of the parameters governing the basic laws of physics–is even more jaw dropping.

MacDonald and Mullan’s work gives a tantalising hint that this idea might be worth pursuing a little more diligently.

Ref: Big Bang Nucleosynthesis: The Strong Force meets the Weak Anthropic Principle

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