I have wanted to write this essay for a very long time now. In the last few years, things kind of came together in a way which made writing it possible. The essay is quite long, and will be difficult to follow for those unfamiliar with the territory. I tried to keep things as simple and straightforward as I possibly could, but there's only so much I could do and still get the key points across. That said, I didn't write this for you, the reader, although I tried to consider you at every turn. I wrote this essay because I wanted to write it, and I enjoyed doing it. The last section can be read separately — Dave
*... or they're very rare
Generally speaking, there are two answers to the question Is There Intelligent Life In The Universe?, where the term "intelligent life" means technologically advanced sentient beings broadly similar to humans. In the first essay I discussed optimistic answers to this question. Optimists imagine a Universe teeming with more advanced versions of ourselves, an answer which coincides (not coincidentally) with their vision of a bright human future.
This week we look at the views of the pessimists, who constitute a small minority of those concerned with astrobiological questions. Pessimists believe that Homo sapiens is alone and unique in the observable Universe, or believe that species broadly similar to Homo sapiens are very rare.
I am a pessimist, a position which follows from prolonged contemplation of the Fermi Paradox, which Paul Davies called "the eerie silence" (see the first essay). Let me begin with an illuminating quote from Lee Billings, whose book Five Billion Years of Solitude was recently published by the Penguin Group (October, 2013).
The book’s title, Five Billion Years of Solitude, is actually a subtle nod to some things I’ve changed my mind about in the course of my research.
It’s a reference to the longevity of Earth’s biosphere. Earth’s life emerged shortly after the planet itself formed some 4.5 billion years ago, and current estimates suggest our world has a good half-billion years left until its vibrant biosphere of diverse, complex multicellular life begins sliding back to microbial simplicity.
When I first began planning this book, I believed that we would eventually find clear signs of life beyond our solar system, and suspected that contact with other cosmic civilizations was just a matter of time, for they were probably common throughout our galaxy. I believed that humans had a future, a destiny, beyond the Earth, and that our discoveries of other habitable or inhabited worlds would galvanize society to strive to voyage to the stars. I no longer hold these beliefs as foregone conclusions.
My optimism for humanity’s long-term prospects has dimmed.
I now believe that while life may be widespread in the universe, creatures like us are probably uncommon, and technological societies are vanishingly rare, making the likelihood of contact remote at best.
I am less confident than I once was that we will find unequivocal signs of life in other planetary systems within my lifetime. I believe that, when seen in the fullness of planetary time, our modern era will prove to have been the fulcrum about which the future of life turned for, at minimum, our entire solar system.
I believe that we humans are probably the most fortunate species to have ever arisen on Earth, and that those of us now alive are profoundly privileged to live in what can objectively be considered a very special time.
Finally, I would guess that though we possess the unique capacity to extend life and intelligence beyond Earth into unknown new horizons, there is a better-than-even chance that we will fail to do so.
The human story may end as it began — in nasty, brutish, and short isolation on a lonely, solitary planet. The book in part is my attempt to explain and come to terms with these beliefs, beliefs that I would very much like to be proved wrong.
The change in Lee's thinking about the human future which occurred as he wrote his book happened to me a long time ago. Unfortunately, prolonged contemplation of the Deep Questions tends to do that to a person.
If you think about it a certain way, generalized pessimism about the human prospect will be easier to accept. What I call "Big Optimism" in humans is an automatic reflex response. It appears to be an innate trait—humans can not assess risks realistically—and certainly such optimism is (literally) mindless in so far as conscious awareness of this response only rarely occurs in the people exhibiting it.
However, if you are actually forced to think about these Deep Questions, as Lee Billings was, discerning people will begin to see the outlines of the true situation of Homo sapiens on the Earth. As it turns out, this Big Picture does not point to a prosperous human future.
You can also think of mindless optimism as part and parcel of anthropocentrism. For humans, a Universe in which our species is eventually crushed by disinterested natural forces (including biological imperatives) beyond its control is unthinkable. Humans literally can not imagine a Universe without humans in it.
Let's examine the arguments of pessimists about the existence of alien "intelligence". Perhaps you will find them as persuasive as I do.
The Problem Of Evolutionary Biology
The problem of evolutionary biology with respect to the existence of technologically advanced alien sentience can be simply stated:
The history of life on Earth is so filled with evolutionary accidents, incidents, coincidences and other random stuff that if, in Stephen Gould's phrase, we "re-ran the tape of life" from some suitably ancient moment in geological time, the species Homo sapiens would certainly not be here now.
Worse yet, it appears to be very, very, very, ..., very improbable that any technologically advanced sentient species would exist on the Earth now. Evolutionary outcomes are highly contingent, and this is especially true in the case of an unusual species like Homo sapiens.
In short, we got lucky! (If you want to call it that; many of you may not because of all the suffering which follows from living among humans.)
Let us first explain contingency in evolutionary biology.
The unpredictability of evolution by natural selection was given by Stephen Gould. Darwin is associated with chance variation but William Paley argued that living things are the products of design [i.e., what is now called "intelligent design"].
Paleontologist George Gaylord Simpson, for each case of directional evolution, either denied the phenomenon or offered an alternative explanation that did not rely on any unknown causal processes. According to Simpson, there were two main reasons to explain why evolution is unpredictable.
The first is that evolution is driven principally by natural selection of chance variations and is termed “opportunistic” as there is no plan or provision by which organisms automatically vary in ways that are adaptive.
The second reason is that there are “multiple solutions” to any environmental “problem”. Gould gave the hypothesis that the traits that predominate in a population are optimal for the environment inhabited by the population, and hence if different traits prevail in different populations, this must reflect environmental differences.
Evolutionary unpredictability is usually contrasted with evolutionary convergence, which is a kind of limited directionality in which evolution tends to come up with the same "solutions" (adaptations) over and over again. I will discuss this subject as the essay progresses.
While admitting that convergence certainly exists in the history of life on Earth, contingency forces us to conclude that evolution has no Grand Plan, especially regarding Homo sapiens. We are not the end product of a 4 billion-year-old process which was "designed"—by whom?, the judeo-christian God?—to bring about a species like us. In short, all teleological interpretations of the history of life on Earth are tragically mistaken. Species come and go. That will happen to Homo sapiens too.
In 1995, Ernst Mayr, one of the founders (along with George Gaylord Simpson) of the 20th century "evolutionary synthesis", debated Carl Sagan, who we recognize as the premier optimist of our time about the existence of alien sentience. I covered Crazy Carl, such as he was, in Part I. This time we will quote the pessimist Mayr at some length, for his remarks go to the heart of the argument for the probable non-existence of technologically-advanced, sentient alien species.
... one must be aware of the fact that evolution never moves on a straight line toward an objective ("intelligence") as happens during a chemical process or as a result of a law of physics. Evolutionary pathways are highly complex and resemble more a tree with all of its branches and twigs.
... After the origin of life, that is, 3.8 billion years ago, life on Earth consisted for 2 billion years only of simple prokaryotes, cells without an organized nucleus. These bacteria and their relatives developed surely 50 to 100 different (some perhaps very different) lineages, but, in this enormously long time, none of them led to intelligence.
Owing to an astonishing, unique event that is even today only partially explained, about 1,800 million years ago the first eukaryote originated, a creature with a well organized nucleus and the other characteristics of "higher" organisms. From the rich world of the protists (consisting of only a single cell) there eventually originated three groups of multicellular organisms: fungi, plants and animals. But none of the millions of species of fungi and plants was able to produce intelligence.
The animals (Metazoa) branched out in the Precambrian and Cambrian time periods to about 60 to 80 lineages (phyla). Only a single one of them, that of the chordates, led eventually to genuine intelligence. The chordates are an old and well diversified group, but only one of its numerous lineages, that of the vertebrates, eventually produced intelligence. Among the vertebrates, a whole series of groups evolved—types of fishes, amphibians, reptiles, birds and mammals.
Again only a single lineage, that of the mammals, led to high intelligence. The mammals had a long evolutionary history which began in the Triassic Period, more than 200 million years ago, but only in the latter part of the Tertiary Period—that is, some 15 to 20 million years ago—did higher intelligence originate in one of the circa 24 orders of mammals.
The elaboration of the brain of the hominids began less than 3 million years ago, and that of the cortex of Homo sapiens occurred only about 300,000 years ago.
Nothing demonstrates the improbability of the origin of high intelligence better than the millions of phyletic lineages that failed to achieve it.
You can see that Mayr is not particularly impressed with Sagan's Billions And Billions. You might think that Ernst has concluded mopping the floor with Carl, but I am delighted to say that there are even more important points for him to make.
Adaptations that are favored by selection [convergent adaptations], such as eyes or bioluminescence, originate in evolution scores of times independently.
High intelligence has originated only once, in human beings.
This is another key point to which I will return in the next section.
I can think of only two possible reasons for this rarity.
One is that high intelligence is not at all favored by natural selection, contrary to what we would expect. In fact, all the other kinds of living organisms, millions of species, get along fine without high intelligence.
The other possible reason for the rarity of intelligence is that it is extraordinarily difficult to acquire. Some grade of intelligence is found only among warm-blooded animals (birds and mammals), not surprisingly so because brains have extremely high energy requirements. But it is still a very big step from "some intelligence" to "high intelligence."
Mayr is of course on to something important regarding the probable non-existence of sentient aliens. First, there is indeed a tendency toward greater encephalization quotients (brain/body ratio, or EQ) in the fossil record, and social mammals (like humans) tend to have larger EQs than other mammals or non-mammals. But the picture is more complicated than it might first appear. These remarks are from Paul Grobstein in the department of biology at Bryn Mawr College.
It is ... possible to talk about both evolutionary trends and evolutionary advantages in relation to a better-defined variable: brain size. For exactly the reasons mentioned above, it is not possible to equate brain size with either intelligence or cognitive abilities.
But studying brain size yields insights that may be relevant nonetheless. Useful observations were documented and discussed in an article by Harry J. Jerison in Scientific American ('Paleoneurology and the Evolution of Mind", January 1976.) [See the first graph below.]
Brain size—or, more accurately, brain size in relation to body size—has clearly increased over evolutionary time, not only in human lineages but in those of many other groups of organisms as well.
In general, however, what has occurred is not the replacement of smaller-brained organisms by larger-brained ones but rather an expansion of the range of brain sizes: larger-brained organisms appear later in time, but smaller-brained organisms continue to persist. The only really valid criterion for evolutionary success is current existence, so the conclusion would seem to be that large brains do not, in general, confer an evolutionary advantage over small brains. Instead large and small brains seem to represent different but equally good evolutionary outcomes.
It is helpful to bear in mind that trends in evolution do not necessarily mean that later-appearing organisms have an evolutionary advantage (that is, are in some way 'better than') over earlier ones. This important general principle most likely applies in the cases of intelligence and cognitive ability, however one comes to understand those terms. Evolution is the continuing exploration of the viability of randomly created variants of preexisting life-forms. Hence, a feature that appears later in evolution means that it is a novel alternative, but not necessarily a ' better' one.
That much is reasonably clear, but it leaves an intriguing, nagging question, along with some additional observations about brain size. There certainly seem to be some meaningful mental attributes that humans (and at least some other contemporary organisms) have more of than did prior ancestors. Furthermore, the recent human lineage (and at least some other animal lineages) does seem to show not only the emergence of creatures having larger brains but in addition their replacement of creatures having smaller brains.
A comparison of the encephalization quotients (EQ) of mammals and reptiles from Jerison (1976). I've edited the graph to show where modern humans are. Importantly, note that this graph uses a log/log scale, which means the human anomaly may not be noticeable at first glance. See the graph and text below. Also see my post The Incredible Shrinking Brain for a few additional details.
The EQs of living mammals. "The results of these studies was presented in the frequently cited "Brain Size in Vertebrates" by van Donger in The Central Nervous System of Vertebrates,Vol 3, 1998.... This (log/log) plot, the slope of which demonstrates that brain size grows as the 3/4 power of body mass, shows that most fall close to the line. Above the line, a species is "smarter than they should be", and if below the line, not so much. Humans are "best" in this regard, although some small rodents and dolphins are close. Adding brain mass was found to increase intelligence only if increased brain mass wasn't diverted to sensory or motor capacities, as for elephants or cows. Humans and elephants have virtually the same number of cortical neurons, but there is clearly a great difference in "intelligence". A mouse is as smart as a cow but it has only 1% of the brain size." Source
In the 542 million years since metazoans (animals) became prominent in the fossil record, only one lineage, the hominins, culminated in highly encephalized species like Homo heidelbergensis, Homo neanderthalensis and Homo sapiens [graph below]. The high EQ of these late hominin species is highly anomalous compared with that of virtually all other species which existed throughout the Phanerozoic Eon. Among modern mammals, only certain species of dolphins are close, but one hopes the differences between humans and dolphins are obvious enough so as not to require additional comment.
The Genus Homo — "The March of Progress had many dead ends."
In short, Big Brains came about only once at the very end of 542 million years of animal evolution, so we can be comfortable in saying that such brains are not a common evolutionary trajectory (i.e., do not reflect convergent evolution). In response to Mayr's obvious point, Carl Sagan had only this to say—
But [Mayr's] basic argument is, I think, acceptable to all of us. Evolution is opportunistic and not foresighted. It does not "plan" to develop intelligent life a few billion years into the future. It responds to short-term contingencies.
And yet, other things being equal, it is better to be smart than to be stupid, and an overall trend toward intelligence can be perceived in the fossil record. On some worlds, the selection pressure for intelligence may be higher; on others, lower.
Sagan's assertion that there is an "overall trend toward intelligence in the fossil record" is misleading. As Grobstein points out, there has not been a replacement of smaller-brained organisms by larger-brained ones but rather an expansion of the range of brain sizes.
The jury is still out on whether it is "better to be smart than stupid," all other things being equal, although if we go by current trends, the eventual answer is going to be resounding No. Grobstein's interpretation of the fossil record is correct—large brains do not confer an evolutionary advantage over small brains. That conclusion contradicts Sagan's assertion.
Worse yet, Sagan seems to be completely unaware of the outrageous anthropocentrism and reflexive optimism of his response to Mayr. Mayr thought scientists like Sagan were unaware of other things as well.
Why are there nevertheless still proponents of SETI?
When one looks at their qualifications, one finds that they are almost exclusively astronomers, physicists and engineers. They are simply unaware of the fact that the success of any SETI effort is not a matter of physical laws and engineering capabilities but essentially a matter of biological and sociological factors.
These, quite obviously, have been entirely left out of the calculations of the possible success of any SETI project.
Mary's point concerns the highly intricate dance of Chance and Necessity (the title of Jacque Monod's book on this subject.) As Michael Shermer once said in Skeptic Magazine (Vol. 14, No. 2, 2008)—
I have noticed an interesting difference between the SETI optimists and evolutionary pessimists (we would consider ourselves realists). And that is that astronomers traffic in the rule of nature's laws, which are repetitive, reliable and necessary, whereas biologists traffic in the chain of accidents, which are quirky, chancy and contingent. Among biologists, no one has emphasized the role of contingency more than Stephen Jay Gould... [see above]
I would take this comparison much further. I am talking about techno-optimism of course. While such types are not entirely unknown among biologists, the vast majority of them are physicists, chemists, engineers of various sorts, or "visionaries" with some background in the so-called hard sciences (leaving out clueless economists). There are of course rare exceptions to the rule.
My observation is that techno-optimists have a very narrow type of intelligence, but little or no generalized intelligence regarding the human situation. Certainly these optimists are unaware of the strong positive biases which guide their thinking on the narrow range of subjects they tend to consider, including astrobiology. I will leave it at that, because this is a big subject which speaks to Human Nature itself.
The human brain is thought to be the most complex object in the Universe. If that is true, you might think that it would give optimists pause when they claim that functionally equivalent (superior?) biological "objects" arise frequently on other planets revolving around other stars (exoplanets). And there is an excellent reason why inordinately Big Brains did not evolve many times on Earth.
The energy requirements of running such a brain are enormous, which raises all sort of issues about how such an organ could have evolved even once. These energy requirements also impose severe constraints on what sort of animal could satisfy those requirements (e.g., meat-eating omnivores versus herbivores).
It's a disappointment—given the unfathomable human-caused suffering and general stupidity which characterize the Human Condition, those 100 billion neurons amount to a whole lot of shucking for not much corn
Ernst Mayr thought SETI was pointless. I do not because the longer "the eerie silence" goes on, the more probable it becomes that it might finally occur to humans that there may indeed be something special about their existence on Earth. And if that's true, then maybe, just maybe, it might occur to them that flushing this golden opportunity down the drain is a big, big mistake.
Woodpeckers, Earth-Centrism And Universality
In his 1991 book The Third Chimpanzee, Jared Diamond included a chapter called Alone In A Crowded Universe (pp. 205-215). In that chapter Diamond uses the evolution of woodpeckers to argue that humans may be alone in the observable Universe. That argument is worth looking at.
Diamond looks at evolutionary convergence as we did above, which is the strongest argument (outside of the sheer LARGENESS of the Universe) for the probable (even common) existence of technologically advanced sentient beings elsewhere in the Milky Way.
... life on Earth is characterized by what biologists term convergent evolution. That is, seemingly whatever ecological niche or physiological adaptation you consider, many groups of creatures have converged by evolving independently to exploit that niche, or to acquire that adaptation.
An obvious example is the independent evolution of flight by birds, bats, pterodactyls, and insects. Other spectacular cases are the independent evolution of eyes, and even of devices for electrocuting prey, by many animals...
There’s nothing surprising about the seeming ubiquity of convergent evolution. If you expose millions of species for millions of years to similar selective forces, of course you can expect similar solutions to emerge time and time again.
We know that there has been much convergence among species on Earth, but by the same reasoning there should also be much convergence between Earth’s species and those elsewhere.
Hence, although radio communication is one of those things that happens to have evolved here only once so far, considerations of convergent evolution lead us to expect its evolution on some other planets as well.
As the Encyclopedia Britannica puts it, “It is difficult to imagine life evolving on another planet without progressing towards intelligence.”
That's the argument. You will recognize the Teleological Error in that Encyclopedia Britannica quote (discussed above). Remember, evolution is not going somewhere, it is not progressing towards anything at all, let alone the development of a species which builds radio telescopes.
Diamond then makes the standard move, noting that such optimistic reasoning does not square with Fermi's Paradox—where are the aliens we would expect to see? Now, lets consider these woodpeckers.
Woodpeckers provide a good test case, because woodpecking is a terrific life-style that offers much more food than do flying saucers or radios.
The “woodpecker niche” is based on digging holes in live wood and on prying off pieces of bark. That means dependable food sources all year round in the form of sap, insects living under bark, and insects burrowing into wood. It also means an excellent place for a nest, since a hole in a tree affords protection from wind, rain, predators, and temperature fluctuations. Other bird species besides woodpeckers can pull off the easier feat of digging nest holes in dead wood, but there are many fewer dead trees than live trees available.
These considerations mean that if we’re counting on convergent evolution of radio communication, we can surely count on convergent evolution among many species to exploit the woodpecker niche. Not surprisingly, woodpeckers are very successful birds. There are nearly two hundred species, many of them common. They come in all sizes, from tiny birds the size of kinglets up to crow-sized. They are widespread over most of the world, except on oceanic islands too remote for them to reach by flying. 18.
How hard is it to evolve to become a woodpecker? Two considerations might seem to suggest “Not very hard"...
Diamond covers the two considerations, and then gets to the heart of his argument.
Thus, while woodpeckers have many adaptations for woodpecking, most of those adaptations have also evolved convergently in other birds or animals, and the unique skull adaptations can at least be traced to precursors.
You might therefore expect the whole package of woodpecking to have evolved repeatedly, with the result that there would now be many groups of large animals capable of excavating into live wood for food or nest sites.
But all modern woodpeckers are more closely related to each other than to any non-woodpecker, proving that woodpecking evolved only once.
Even on remote landmasses that woodpeckers never reached, like Australia, New Guinea, New Zealand, nothing else has evolved to exploit the splendid opportunities made available by the woodpecker life-style. Some birds and mammals on those landmasses do excavate dead wood or bark, but they are only feeble excuses for woodpeckers, and none can excavate in live wood. If woodpeckers hadn’t evolved that one time in the Americas or Old World, a terrific niche would be flagrantly vacant over the whole Earth.
I have dwelt on woodpeckers to illustrate that convergence is not universal, and that not all splendid opportunities are seized. I could have illustrated the same point with other, equally flagrant examples...
Regardless of whether we're talking about woodpeckers or big-brained, bipedal primates who build radio telescopes, convergent evolution on Earth does not entail that such creatures evolved elsewhere in the Universe, nor does it imply that such developments were probable. There is no "woodpecker niche" on Earth, nor is there a "big brain niche" which evolution on Earth (or elsewhere) necessarily fills up in the fullness of time.
And now, let's raise the ante. The discerning reader will have noticed that we have been talking about evolution on Earth. Aren't we generalizing from one example? Surely things might have gone differently on other planets revolving around other stars.
This "Earth-centric" (but not anthropocentric) reasoning may not be as much of a mistake as it is commonly made out to be. It's true, we would be very happy to have another informative "complete" example of the evolution of life on another world over billions of years, but we don't have one and we're not going to get one.
This raises the very important question of what we might consider universal (as in "necessarily applying everywhere in the Universe") as opposed to what is contingent and local (as in "applying in some places sometimes, but not necessarily").
I will not beat around the bush—here are the universal principles I am assuming.
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The laws of physics and chemistry are the same everywhere in the Universe. Thus the very foundations of biochemistry are very likely the same everywhere in the Universe. To evolve life, you need liquid water, an energy source, and complex organic (carbon-based) molecules—the so-called "building blocks of life". If you're looking for silicon-based complex life, or other exotic varieties of complex life based on non-carbon biochemistry, you can stop looking. If you want "advanced" life (metazoans, aka. animal life), you need large amounts of free oxygen to support respiration or some functionally equivalent mechanism to meet the energy requirements of large, complex organisms.
Free oxygen levels in Earth's atmosphere over geological time, from Nick Lane's Life's A Gas (New Scientist, February, 2010).
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We assume the universality of evolution itself. To go from simple (prokaryotes, i.e., bacteria, archaeans) to complex (metazoans) and on to "advanced" beings like Homo sapiens, life must pass through a series of major macroevolutionary stages (see the next section below). At the level of microevolution, evolution proceeds by a process of replication (which is DNA-based on Earth) with mistakes (copying errors). These "mutations" are evaluated (as successful or failing) with respect to an ever-changing external environment. Beneficial mistakes are perpetuated, disadvantageous mistakes are eliminated from the "gene" pool or its alien equivalent. These step-wise changes (with respect to the external environment) lead to branching in the tree of life (speciation).
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In very "advanced" life forms, such as Homo sapiens or broadly similar species elsewhere in the Universe, evolution may proceed in a way which is seemingly independent of the environment along "cultural" lines, which accounts for, among the countless examples which could be brought to bear here, the seemingly improbable existence of Kei$ha, Alex Jones and Paul Krugman. Clearly, if evolution were working properly as defined above, these humans and many, many others much like them would have ceased to exist some time ago
You may think these are unrealistic assumptions, but to me (and most astrobiologists) they seem quite reasonable. Bear these assumptions in mind as you read on.
Hard Evolutionary Steps And Eukaryotes
You will recall Stephen Gould's famous remark about re-playing the tape of life. Gould concluded that if we had an opportunity to do so, if we could run "the experiment" again and again, we would very likely not find a big-brained, bipedal primate like Homo sapiens at the end of the run.
Obviously we can not do that and will never be able to do it. Our inability to run realistic simulations, combined with our complete lack of observational evidence from other worlds, means that we have no experiential (a posteriori) knowledge of how probable an evolutionary event is. Just as obviously, we do not know a priori (as deduced from first principles) how probable some evolutionary event was. We are in the dark.
That said, we can pick out critical steps in the evolution of life on Earth which led to metazoans and, eventually, to Homo sapiens. We must make educated guesses about the difficulty (relative probablility) of each of these critical steps. There is a good enough (if not fool-proof) method for determining whether a critical macroevolutionary step was hard, where a step is critical if we would not be here had it not occurred.
If a critical macroevolutionary step occurred only once in the history of life on Earth, it seems reasonable to posit that the step in question was improbable (hard).
A quote from Mark Twain comes to mind here.
There is something fascinating about science. One gets such wholesale returns of conjecture out of such a trifling investment of fact.
I hope to convince you that Twain's observation doesn't necessarily apply in the case of the probable absence of sentient aliens in the Milky Way. Before I get to a specific result which turns mere conjecture into solid science, I need to set some things up.
In a 1983 paper called The anthropic principle and its implications for biological evolution, physicist Brandon Carter laid out a research program which has borne much fruit for pessimists on the alien question. Carter concluded that "civilizations comparable with our own are likely to be exceedingly rare, even if locations as favorable as our own are a common occurrence in the galaxy."
I have never been able to get a copy of Carter's original paper, but I can reconstruct a version of his argument from the accounts of others (see the text box below). I shall expand on the required concepts in two short articles directly below the box. Also, you must put up with some notation:
"≈" means approximately equals
">>" means much greater than
"<<" means much less than
Brandon Carter's 1983 Argument There is no reason to believe that the habitable period of a life-bearing planet revolving around a main-sequence star like the sun should be related in any way to the time it takes for complex, intelligent (radio-telescope using) life to evolve on that planet.
Taking these as independent uncorrelated variables, let us define them:
t* = the habitable period of a life-bearing planet revolving around a main-sequence star
tb = the time required for complex, intelligent life to evolve on that planet
In our own solar system, the only example of complex, intelligent life we have, we observe that the values of these seemingly independent variables are quite close to each other within the same order of magnitude.
t* ≈ tb
where t* = (approx.) 5.5 billion years, and tb = (approx.) 4.55 billion years
In so far as nothing links the two variables, this looks like a bizarre coincidence.
However, there is an observation selection effect (an anthropic bias, and here) in which the only available "evidence has been filtered by the precondition that there be some suitably positioned observer" who considers that evidence. This next quote is from Andrew Watson's important 2008 paper Implications of an Anthropic Model of Evolution for Emergence of Complex Life and Intelligence. Watson's paper is based on Carter (1983).
"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."
More formally, Carter reasoned like this—
In general, it should be the case that
(1) t* >> tb
or
(2) t* << tb
but we observe
(3) t* ≈ tb
in the only example we have. Since what we observe (3) is very improbable given the assumed independence of the two variables, and since (1) seems very improbable because we observed (3) in the first case we know of (our own solar system), it must be the case that (2) is generally correct, meaning that in the presumed normal case, the time it takes for complex, intelligent observers to arise (tb) is much, much longer than the time available for that evolution to occur (t*).
Thus an observer selection effect (anthropic bias) explains why we observe (3).
This simple but ingenious reasoning explains why we observe no other complex, intelligent civilizations, and strongly suggests that the evolution of such civilizations is constrained by the existence of some number of very difficult, improbable macroevolutionary steps.
Improbably, life on Earth made it through all prior hard steps and, consequently, we are here to speculate about the existence of aliens.
In short, we got lucky.
If Carter's argument seems hard to understand, here is a similar, simpler argument from The Great Filter, Branching Histories and Unlikely Events by David Aldous, a statistician at the University of California.
The generally accepted answer to the question
have we observed evidence of extraterrestrial intelligence, either contemporary (e.g. via radio astronomy) or in the past (e.g. evidence of previous visits to the solar system)?
is "No".
From this single bit of data, much speculation has resulted, under the names the Fermi paradox and Drake equation. The topic is discussed at length in two non-technical books [Paul Davies' The Eerie Silence and Stephen Webb's If the Universe Is Teeming with Aliens ... Where Is Everybody? — Fifty Solutions to the Fermi Paradox and the Problem of Extraterrestrial Life.]
Consider the product
(1) Npq
where
N is the number of Earth-like (loosely, and at formation) planets in the galaxy
p is the chance that, on such a planet, an intelligent species at a technological level comparable to ours will sometime arise
q is the chance that such a species would continue in such as way as to be observable (via communication or exploration) to other galactic species for an appreciable length of time.
... The point is that Npq represents the number of other intelligent species we expect to observe in the galaxy. Because we don't observe any, we conclude prima facie (treating absence of evidence as evidence of absence) that it cannot be true that Npq >> 1. Since it would be a bizarre coincidence if Npq ≈ 1, we should conclude that Npq << 1 and so humans are most likely the only technological species in the galaxy.
The Aldous version leaves out the temporal dimension and anthropic bias which are central to Carter's argument. Scientists have figured out that the expected future habitability of the Earth is only about 1 billion years, as discussed in Science Daily's What Are The Odds Of Finding Extraterrestrial Intelligent Life? (April, 2008). This was their report on Andrew Watson's paper.
Structurally complex and intelligent life evolved late on Earth and it has already been suggested that this process might be governed by a small number of very difficult evolutionary steps.
Prof Watson, from the School of Environmental Sciences, takes this idea further by looking at the probability of each of these critical steps occurring in relation to the life span of Earth, giving an improved mathematical model for the evolution of intelligent life.
According to Prof Watson a limit to evolution is the habitability of Earth, and any other Earth-like planets, which will end as the sun brightens. Solar models predict that the brightness of the sun is increasing, while temperature models suggest that because of this the future life span of Earth will be ‘only’ about another billion years, a short time compared to the four billion years since life first appeared on the planet.
“The Earth’s biosphere is now in its old age and this has implications for our understanding of the likelihood of complex life and intelligence arising on any given planet,” said Prof Watson.
“At present, Earth is the only example we have of a planet with life. If we learned the planet would be habitable for a set period and that we had evolved early in this period, then even with a sample of one, we’d suspect that evolution from simple to complex and intelligent life was quite likely to occur.
By contrast, we now believe that we evolved late in the habitable period, and this suggests that our evolution is rather unlikely. In fact, the timing of events is consistent with it being very rare indeed.”
Prof Watson suggests the number of evolutionary steps needed to create intelligent life, in the case of humans, is four. These probably include the emergence of single-celled bacteria, complex cells, specialized cells allowing complex life forms, and intelligent life with an established language.
“Complex life is separated from the simplest life forms by several very unlikely steps and therefore will be much less common. Intelligence is one step further, so it is much less common still,” said Prof Watson.
His model, published in the journal Astrobiology, suggests an upper limit for the probability of each step occurring is 10 per cent or less, so the chances of intelligent life emerging is low – less than 0.01 per cent over four billion years.
This is figure 1 from Watson (2008). Click to enlarge.
Regardless of what Watson's model says about the chances of intelligent life emerging, it behooves us to look at a list of generally agreed upon (at least among astrobiology pessimists) "difficult steps" which must be traversed sequentially in order to get from prokaryotes to big-brained bipedal apes with iPhones. All this took at least 3.5 billion years (going by the earliest fossils).
This list is a simplified amalgamation of other lists. The main source of the list is Watson (2008), which in turn is based on John Maynard Smith and Eors Szathmary's influential book The Major Transitions in Evolution (1995). The first three entries cover the origin of life itself, which led to LUCA, the last universal common ancestor of all life on Earth.
1. replicating molecules to populations of such molecules2. unlinked replicators to chromosomes
3. RNA as gene and enzyme to DNA and protein (genetic code)
4. oxygenic photosynthesis
5. prokaryotes to eukaryotes
6. asexual clones to sexual populations
7. protists to animals, plants, and fungi (cell differentiation among the eukarya)
8. tool-using animals with big brains (hominids)
9. a "successful" big-brained species, planetary expansion, space exploration
10. colonization of the galaxy (Fermi's Paradox, it appears this has never occurred)
You will recall that our criterion for the "hardness" of a critical evolutinary step is that the step in question occurred only once. Skipping over the earlier "origin of life" steps, we have several good candidates, including but not necessarily limited to steps #4, #5, #8, #9 and #10. In a later 2008 paper, Brandon Carter considered a scenario with 5 or 6 difficult macroevolutionary steps.
Step #10 has never occurred as far as we know, so that's the problem we're looking to solve. Step #9 is where the human species is now. But nobody seems to have made the transition from #9 to #10. That's pretty alarming if you take some time to think about it. (You can read about the so-called "Great Filter" here and here.)
There are excellent reasons to focus on step #5, the transition from prokaryotes (bacteria, archaeans, image above) to simple (early) eukaryotes with mitochondria. If we can demonstrate that only one of these steps was incredibly improbable, we have effectively explained why we don't see any sentient aliens. As the old saying goes, the proof of the pudding is in the eating.
As far I can see, the work of evolutionary microbiologist Nick Lane of University College London has been largely ignored by astrobiologists, most of whom are astronomers, geophysicists, and so on—these Carl Sagan-types tend to ignore biology and evolution, as I said above. It's a damn shame because Nick is making alien optimists look bad everytime he writes a book or makes a video. Here, in a nutshell, is what you need to know about the origin of protists (e.g., amoebas, paramicium) and eurkaryotic cells—
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it only occurred once, perhaps as early 2.2 billion years ago near the end of the Great Oxygen Event (GOE) pictured in a previous section. All eukaryotic organisms and cells evolved from a common ancestor.
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this solitary event occurred in a non-standard way which lies outside the realm of microbiology (genetic change w.r.t. an external environment) when one prokaryote "swallowed" or engulfed another (a process which occurred many times after eukaryotes became established, e.g., in the evolution of photosynthetic plants). The merger was successful somehow, and the absorbed bacterium apparently became the first mitochrondrion (pl. mitochondria). Mitochondria are the "energy factories" of eukaryotic organisms and cells.
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according to Lane, there was basically no other way eukaryotes could have emerged due to the higher energy requirements of very large single-celled organisms like the earliest protists. Single-celled bacteria could never have achieved this on their own.
That, ladies and gentlemen, is a recipe for mindboggling improbability. I am not going to get into the details because Nick can do that himself in the two videos below. I will also reprint this 2010 New Scientist report Why complex life probably evolved only once. I have highlighted the last section because in respect to astrobiology and our existence on this Earth, it may be the most important text you will ever read.
The universe may be teeming with simple cells like bacteria, but more complex life — including intelligent life — is probably very rare. That is the conclusion of a radical rethink of what it took for complex life to evolve here on Earth.
It suggests that complex alien life-forms could only evolve if an event that happened just once in Earth's history was repeated somewhere else.
All animals, plants and fungi evolved from one ancestor, the first ever complex, or "eukaryotic", cell. This common ancestor had itself evolved from simple bacteria, but it has long been a mystery why this seems to have happened only once: bacteria, after all, have been around for billions of years.
The answer, say Nick Lane of University College London and Bill Martin of the University of Dusseldorf in Germany, is that whenever simple cells start to become more complex, they run into problems generating enough energy.
"It required a kind of industrial revolution in terms of energy production," says Lane. "[Our hypothesis] overturns the traditional view that the jump to complex eukaryotic cells simply required the right kinds of mutations."
"It is very, very convincing, in my opinion," says biologist John Allen of Queen Mary, University of London, on whose work Lane and Martin have drawn.
Growing costs
To become more complex, cells need more genes and more proteins – and so they need to get bigger. As the volume of any object increases, however, its relative surface area falls: an elephant has less surface area per unit of volume than a mouse, for instance. This is a major problem because simple cells generate the energy they need using the membrane that encloses them.
Lane and Martin calculate that if a bacterium grew to the size of a complex cell, it would run out of juice. It might have space for lots of genes, but it would have barely enough energy to make proteins from them.
Folds don't help
In theory, there is an easy answer to the energy problem: create lots of folds in the cell membrane to increase its surface area, which in turn will increase the amount of energy the membrane can produce. Indeed, many bacteria have such folds. But this leads to another problem as they get larger.
Producing energy by "burning" food is playing with fire. If the energy-producing machinery straddling the membrane is not constantly fine-tuned, it produces highly reactive molecules that can destroy cells. Yet fine-tuning a larger membrane is problematic because detecting and fixing problems takes longer.
These obstacles were overcome when a cell engulfed some bacteria and started using them as power generators – the first mitochondria.
By increasing the number of mitochondria, cells could increase their membrane area without creating maintenance problems: each mitochondrion is a self-contained system with built-in control and repair mechanisms.
Birth of complexity
Once freed from energy restraints, genomes could expand dramatically and cells capable of complex functions – such as communicating with each other and having specialised jobs – could evolve. Complex life was born.
So if Lane and Martin are right, the textbook idea that complex cells evolved first and only later gained mitochondria is completely wrong: cells could not become complex until they acquired mitochondria.
Simple cells hardly ever engulf other cells, however – and therein lies the catch. Acquiring mitochondria, it seems, was a one-off event.
This leads Lane and Martin to their most striking conclusion: simple cells on other planets might thrive for aeons without complex life ever arising. Or, as Lane puts it:
"The underlying principles are universal. Even aliens need mitochondria."
Journal reference: Nature, vol 467, p 929
Here's the short version.
Here's the long version.
Astrobiology And The Meaning Of Everything
I've seen things you people wouldn't believe. Attack ships on fire off the shoulder of Orion. I watched c-beams glitter in the dark near the Tannhauser gate. All those moments will be lost in time... like tears ... in rain... Time ... to die
— Roy Blatty, replicant in Blade Runner (1984)
Keen, unbiased observation of humans reveals time and again that they are very confused. However, when animals with big brains became conscious, so did the observable Universe. The existence of sentient observers means that the Universe can contemplate itself—it became self-aware. In equal measure, we are disappointed about the weak, confused nature of human awareness even as we are astonished that it exists at all.
If we are searching for the meaning of everything, including our own existence, consideration of that disappointment and astonishment is where the discussion must begin. The rest of this essay is philosophical. If I have not demonstrated to your satisfaction that our existence on this planet is the outcome of a long series of improbable evolutionary events, nothing further I could say will persuade you. You might also bear in mind that I've merely scratched the surface in describing some (but not nearly all) of the Good Fortune which made our existence possible. We got lucky.
Contemplation of the sentient alien existence question forces us to deal with human confusion and our disappointment in the Human Condition. In the historical past, humans usually attributed their Good Fortune to unseen powers—the god(s) or, earlier on, the ancestors—who watched over them, or who had to be appeased to keep that lucky streak going. I don't want to make a sweeping generalization here because the human relationship to the god(s) has all the complexity of human relationships to other humans.
That observation isn't surprising because the god(s) are a human invention, and thus subject to the same unconscious psychological projections humans always make. Today such attribution goes by the name intelligent design, even if this fundamentally religious view has been modified somewhat to accommodate the existence of scientific knowledge, for example, the god who fills in the gaps (what is missing) in our scientific knowledge. Confusion reigned and, in some quarters, still does.
Under this benighted view, humans were special in a way consistent with their religious beliefs. Science overthrew that view when Copernicus and many others demonstrated that the Earth is one planet revolving around one star in a very, very, (etc.) BIG universe. But then these scientists threw out the baby with the bathwater when they decided that if there is nothing special about the Earth and the solar system, that must mean there is nothing special about our own existence. In astrobiology, that is the very question which requires an answer. These scientists can not allow themselves to be astonished by our existence. Instead, these "optimists" are searching for future successful versions of themselves in outer space. Confusion reigns again.
All of which brings me to the all-important longevity question, which I have not talked about up to now. It's a simple question. It was Deckard's question in Blade Runner—it is now 2013 by our own reckoning, how much time have we got?
It is a standard question in astrobiology. In fact, that question is right there in the Drake equation (see Part I). One answer to Fermi's Paradox says that all extraterrestrial civilizations broadly similar to ours destroyed themselves. These ETCs came into existence and then winked out in the blink of an eye. It's a compelling story because our misnamed species Homo sapiens—Homo laeviculus?—is destroying its Earthly environment, and on the geological time scale, this tragic outcome is taking place in basically no time at all (within a few centuries, at most 1000 years on current trends).
And now we return to our disappointment and human confusion. (There's no escaping it.) Years ago, I would ask myself a simple question—what's the worst possible outcome? I have long been interested in astrobiology, and in that context, the answer to this question was simple too—we are alone, or at the very least we are effectively alone, and we are fucked. It looks like that worst possible outcome is coming true. At least, I will die convinced that it's true. I see nothing which would cause me to change my mind.
Later on in my contemplation of the meaning of everything, I started asking another question which required an answer—why is the news about Homo sapiens always so bad?
Well, to answer that question, we have to ask another—what's the situation? I will mix in an astrobiological perspective as we look at the Big Picture. We need to look at our disappointment and human confusion, we need to look at some inconvenient truths to use Al Gore's pithy phrase. Of course, Gore himself would agree with none of this, for like most everybody else, his anthropocentric, overly optimistic secular religion tells him that humans are marching to the drumbeat of Perpetual Progress. Ignoring Gore's irreparable confusion, let's look at the situation.
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First and foremost, humans are animals. I have to say it because humans no longer remember it, which of course does not make this observation less true. As animals, humans evolved to become what they are, evolved to create the human-made world of the 21st century. (I am a determinist.) If broadly similar extraterrestrial civilizations arose on other planets revolving around other suns, however widely scattered in space and time, the "lucky species" in question would be (would have been?, will be?) animals too. They would have evolved just like we did, although the details of their evolution would be somewhat different—not altogether different—than the way things went on Earth.
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DOTE readers will be familiar with my catch-phrase Homo sapiens is a species, so what you see is what you get. I attempted to capture some of our species-specific characteristics in my post Flatland — A "Good Enough" Theory Of Human Cognition. What is of particular interest to me is that cognitive or neuroscientific research by those studying these Big Brains of ours is slowly but surely uncovering a picture of unconscious cognition which looks one hell of a lot like Flatland!
My answer to the "always bad news" question I posed above is that you can chalk it up to faulty wiring, which is the relationship of the conscious, self-aware mind to the vast unconscious sea underlying it. That's the source of human confusion and our disappointment. For example, humans are destroying marine ecosystems at an alarming rate. If humans destroy most animal life in the oceans, they will ultimately destroy themselves. Why are humans doing this? Why do they continue to do it, despite dire warnings from marine scientists? My answer? Bad Wiring! That's why humans can not acknowledge or even see that they're destroying vital marine ecosystems, even though the pertinent research is out there in public view. In the Internet Age, anybody can access and consider it.
Anthropocentrism and mindless optimism (among other biases) arise from the fact that we are animals, and thus we were "designed" by Nature to be self-centered. These biases are hard-wired in the brain. I have called this the Human Conceit. It is therefore amazing that a few people can "back away" sufficiently from the Human Condition to see it for what it is, at least in part. It is equally predictable that only a few people are able to do so. Their inability to see themselves "objectively" from a psychological distance keeps humans mired in confusion (they can not escape their basic frame of reference). Humans are thus imprisoned in Flatland. Their confinement means they can not escape their Fate.
From an astrobiological perspective, the question becomes whether sentient aliens broadly similar to us would be wired the same way we are. As I said, these unseen aliens would be animals, they would have evolved in some way broadly similar to the way we evolved. Would they have the same flaws, the same bad wiring that we do? I don't know. Aliens with a different consciousness might be able to assess risks realistically. Humans lack this ability when doing so runs counter to deeply ingrained (innate, instinctual) social behaviors. Aliens might view sustaining growth in populations and economies as choices they can make. At the level of populations, humans don't exercise choice in these aspects of life (for example, anthropogenic climate change requires scaling back of human economies). There does seem to be something inevitable (necessary) about the way we're wired, given the way evolution works, but who knows? If sentient aliens were a lot like us, they most likely destroyed themselves just as we're doing (via habitat destruction and, eventually, resource depletion), though not necessarily in the same way.
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From a Big Brain perspective, what we humans are now is As Good As It Gets. Humans are still evolving—there are still genetic mutations and there is still an external environment by which these are evaluated—but such microevolution only amounts to minor tinkering at this point, considering the relatively short time remaining.
So-called "cultural" evolution is happening very, very quickly now—we're going nowhere fast
—but biological evolution, especially in large, complex "advanced" animals like humans, or chimpanzees for that matter, occurs very, very slowly on human time scales. Humans have been basically the same for about 200,000 years, although some paleoanthropologists argue that some major brain re-wiring occurred about 50,000 years ago. Maybe so, but that doesn't change the human prospect. If current trends continue, and there's no reason to believe they won't, we don't have 50,000 years to see how it all turned out.
In fact, the situation looks even worse when we consider recent scientific results which suggest that humans are as smart as they're going to get (and see here). That conclusion comes as a result of physical constraints on brain expansion and processing power (in neural network terms). So we're back to where we started—Homo sapiens is a species, so what you see is what you get.
You Are Here (click to enlarge)
Despite all these very disappointing and inconvenient truths, here we are. The human optimist will say there aren't any problems, the human pessimist predicted last week that this week was literally the last week we would be here, and the human realists, all 17 of them, say well, things look really bad, but the astonishing fact is that we're still here. And the most astonishing fact of all is that we were ever here to begin with.
Revel in your time! Be heartbreakingly aware that you are a (partially) conscious living being, a sentient observer of this Earth and the rest of this really, really, (etc.) BIG Universe. I know from much personal experience how hard this is to do because, let's face it, life among Homo sapiens entails a whole lot of suffering because humans are such egregious fuck-ups. They're very confused. It's very disappointing. Get over it. That's the only answer. There are no other answers.
And, hell, we humans can't really explain why there is anything at all (matter and energy) instead of nothing. A Big Bang? 13.82 billion years ago? What the fuck! We'll never know why there is something instead of nothing. That's just the way it is. Get over that, too, just in case you've ever thought about it.
And that, ladies and gentlemen, as far as I can see, is the meaning of everything.
Revel in your time because someday this astonishing movie is going to end.
Dave Cohen
Decline Of The Empire
November 3, 2013
Dave -- I have followed you on and off for many years -- since you were contributing to TOD in fact. Your piece above is the best I have seen on the subject. Gene B
Posted by: gene b | 11/03/2013 at 01:54 PM