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It's Lonely Out There – The Evolutionary Explanation For The Fermi Paradox

by John Lambshead




The Fermi Paradox is named after Enrico Fermi, who postulated it in 1950 during informal discussion. It can be summarised as: if the truth is out there, why haven't we seen some evidence? Or to put it another way, where are the intelligent aliens? Not a single shred of evidence has ever been found of a piece of technology that is not human. All around us broods a silent universe, the silentium universi (things sound so much more authoritative when translated into Latin, don't you think?).

Physicists have dominated discussion on the Fermi Paradox, Fermi was a physicist, because it appears to be an issue of astronomy. But actually it is an issue of biology since it is about evolution.

In this paper I am going to address two points: How common is life in the universe, and how common is intelligent life. To gain an insight into the second point, I will be obliged to consider how intelligent life might evolve. For the purposes of this essay, intelligence is defined as human-level intelligence, i.e. the capacity to create a technological civilization.

Of course there are a number of explanations for the paradox of varying degrees of tinfoil-hatted looniness. For example, the Area 51 conspiracy theories to the effect the evidence exists but has been suppressed by the "government." Presumably, this is the one world secret government of giant shape-changing lizards from Draco – sorry, I have been reading David Icke's website again. It's one of those things that make you wonder whether there really is intelligent life on Earth.

You may be blissfully unaware that the world is actually run by a conspiracy of reptiloid aliens known as the Babylonian Brotherhood. Scaly-skinned members include George W Bush, Queen Elizabeth II and Boxcar Willie.

Boxcar Willie?

Moving swiftly on, less lunatic explanations of the paradox are simply untestable and hence pointless. Examples include the idea that alien technology is undetectable because it is too advanced for our primitive monkey brains to comprehend or is simply too, um, alien. For example, consider the Hooloovoos, hyperintelligent shades of the color blue (according to the Hitchiker's Guide to the Galaxy). How do you detect the existence of hyperintelligent shades of the color blue?

Another untestable possibility is that aliens are deliberatively quarantining Earth for some social, scientific or alien reason. This is known somewhat unflatteringly as the Zoo Hypothesis. Presumably, some pettifogging minor official in the Galactic Central Bureaucracy has decided that we are not ready, or worthy, or whatever, to join the great Galactic Society.

Douglas Adams, who else, had a slant on this. He suggested Earth was located in Galactic Sector ZZ9 Plural Z Alpha in the unfashionable uncharted end of the Western Spiral Arm, so guests are unlikely to drop by while in the neighbourhood. Sort of like living in Birmingham, or a flyover state in the USA.

The building of a new hyperspatial highway through the Sector should have solved the problem, were it not that the Earth was in the way so had to be demolished by a Vogon constructor fleet. I believe the corporate psychopaths call that creative destruction, something about eggs and omelettes.

I raise these points simply to dismiss them. We have to assume that if the universe teems with intelligent life then it will be enough like us that we could detect its activities. Otherwise, there is nothing to discuss.

The Fermi Paradox has been explained by something called the Rare Earth Hypothesis. This suggests that the Earth is uniquely capable of supporting intelligent life because of an extremely rare combination of favorable circumstances. The hypothesis was coined by Ward and Brownlee, who interestingly are not physicists, but a geologist/palaeontologist and astronomer/astrobiologist respectively.

The issue with the Rare Earth is that it is the antithesis of the Principle of Mediocrity, also known as the Copernican Principle, which is an important concept in scientific philosophy. Broadly speaking, it goes like this. If you have only one example of something then assume that it is typical of its type. One can think of it as a variant of Occam's Razor (good ole lex parsimoniae). In terms of probability, you are far more likely to be right if you assume ordinaryness rather than uniqueness. Hence Copernican, since Copernicus in 1543 demonstrated the principle by moving the Sun, rather than the Earth, to the center of the universe.

Some seventy years later, the Catholic Inquisition suppressed Galileo's work and labelled him a heretic for pointing out that the Earth went 'round the Sun. Actually, the Catholic Church banned mention of Galileo's and Copernicus' work as late as 1835, not that anyone took much notice. Galileo was not rehabilitated by the Church until a speech by Pope John Paul in 1992.

Before we judge the Church too harshly, it is worth noting that a Dutch television channel censored all reference to evolution in David Attenborough's Life of Mammals and reference to anthropogenic global climate change has been censored from his new series Frozen Earth by American television.

Some scientific conclusions will always be too shocking for the ears of the proles, at least in the opinion of the Establishment. And the Establishment is right to be concerned. Knowledge and ideas are the most dangerous things in the world to the stability of the status quo.

So can we reconcile the principle that the Earth is probably not special to the observation that we can find no evidence for alien civilizations in the rest of the universe? I think we can if we consider evolutionary biology. Most of the debate on this subject is between physical scientists who, inevitably, have a tenuous grasp of biology. My own grasp of quantum mechanics is less than profound so I sympathize. But in this paper, I want to look at the biology of intelligent life and see if it provides a possible solution to the Fermi Paradox.

Let's start with the famous Drake Equation (Frank not David). It is accepted wisdom that one loses half one's audience with every mathematical equation in a paper so I will not copy it out. The equation has seven variables, which means that (i) it will generate all possible probabilities between zero to one depending how the variables are set and (ii) a variety of different variable settings can give the same probability. It is worth pointing out that Drake formulated the equation as an agenda for discussion, not as a predictive or explanatory model.

The variables are:

  1. Rate of star formation.
  2. Proportion of the above stars with planets.
  3. Proportion of the above planets that could support life.
  4. Proportion of the above planets that do support life.
  5. Proportion of the above life that evolves intelligence.
  6. Proportion of the above intelligent life that develops detectable technology.
  7. The life span of civilizations with detectable technology.


You can always add in extra variables; for example Brin (David not Frank) suggested an additional factor for civilizations that colonize new solar systems, but more variables merely add to the problem. It is actually helpful if we can simplify the equation so that is what I’ll do.

With anything like our current state of knowledge, variables three and four must be regarded as a distinction without a difference. We can only be sure a planet could support life if it does support life so we can merge these variables.

Similarly, variables five and six are probably the same thing and can be merged. The only working definition of intelligence in this context is a species that creates a civilization, and using the Principle of Mediocrity we can assume that such a civilization will use detectable technology. I will also ignore the last variable as there is no data, nothing into which to get one’s academic teeth.

That leaves us with just four variables. The first two are astronomic and have been comprehensively discussed elsewhere. I am going to consider the last two: the probability of life evolving on an Earthlike planet and the probability of that leading to a civilization.

To do this I intent to use the evolution of life on Earth as a model, applying Mediocrity, to see if it can explain the Universal Silence.

The oldest minerals on Earth are zircon crystals from Western Australia, about 4.4 billion years old. The oldest solid objects found in our solar system are certain meteorites dated to about 4.6 billion years. So we are probably in the right ball park (now there's an Americanism that has infiltrated British English – I am informed it is something to do with the American version of the game of Rounders) if we estimate the Earth's age to be 4.5 billion years – give or take a million or so. One can be so refreshingly cavalier about inexactitude when dealing with deep time. Evidence from the Moon suggests that there was a massive meteorite bombardment between 3.8 to 4.0 billion years ago so severe that it stripped away any previous atmosphere or oceans. That date sets our baseline for the earliest point for the start of life on Earth.

The universe is calculated to be somewhere in the region of 13.8 billion years so the Earth has existed for the last third of the life of the universe.

Earthlike rocky planets could only form after the first generation of stars spewed out metallic elements in supernovae. These stars probably formed quite quickly after the Big Bang, perhaps after just 0.5 billion years, and most of them had gone by 4.0 billion years. So, to pluck a figure out of the air in the finest traditions of speculative science, many Earthlike planets should have appeared by 5.0 billion years after the Big Bang, or 8.8 billion years ago.

Now let us address the question of how long it might take for life to develop on an Earthlike planet. The first indisputable traces life on Earth are bacterial fossils dated to 3.0 billion years before present. Bacteria are fairly sophisticated prokaryote (lacking a nucleus) cellular organisms. So we have two scenarios. The first is that bacteria arrived from space or that life evolved immediately – and one means immediately – after the bombardment.

For our purposes, the source of life is of no consequence. The key point is that life is found as soon as it was possible. Applying the Principle of Mediocrity, one can only conclude that life must be widespread across the universe, and that it has been knocking round the universe for the last 8.0 to 9.0 billion years.

The next link in our argument chain is to consider when intelligent life, civilization, is likely to appear. The big evolutionary jump is from a prokaryote cell to the much more sophisticated eukaryote cell. Oxygen is a highly reactive, toxic gas that appears in significant quantities in the Earth's atmosphere from around 2.4 billion years ago. We associate modern complex eukaryote cells with oxygen so these organisms were a going concern from at least this time. Oxygen-based metabolism raises biological productivity by around 100 to 1000 times, so the pace of evolution quickens once it appears.

The sophistication of the eukaryote cell makes possible sexual reproduction and multicellular organisms. Multicellularity appears to have evolved more than once so we can conclude that its evolution is probable, although it takes a considerable time (around 1.5 billion years).

Multicellularity allows the cell line specialization necessary for complex organisms such as plants, fungi and animals (incidentally fungi are a sister group of animals not plants). Once metazoa (animals) evolve, the push of evolutionary competition forces life to spread to exploit all possible ecological niches. Some of these niches only become usable by the evolution of increasingly complex organisms. So evolution drives increasing complexity.

A high rate of evolution requires an unstable ecosystem; organisms evolve faster at a time of change. However, too much instability causes localized catastrophe and even global mass extinction because change outruns the ability of organisms to cope. An organism cannot evolve mechanisms to adapt to unexpected catastrophe. The Goldilocks Principle of just the right amount of instability definitely applies.

The first evidence we have for the evolution of a mind capable of creating a civilization is not the manufacture of tools — many species use tools — but the creation of art. Art implies creativity, an ability for abstract thought separate from the mundane.

The first art we have ever found was created by a population that lived about seventy thousand years ago on the southeast tip of South Africa, two hundred miles east of Cape Town. These ancient South Africans engraved abstract (symbolic?) designs onto their artefacts. They also made more sophisticated weapons than had ever been seen before, but it is the art that is significant.

This population was drawn from our species, Homo sapiens, but they are not the first members of our species. H. sapiens evolved in Africa about a quarter of a million years ago from the hominid clade (line), which split from chimps about five million years ago. This raises the possibility that the modern human mind evolved long after the modern human body. I'll come back to this point.

So we have a time line for intelligent life on Earth. Life appears almost immediately but intelligent life took nearly four billion years to evolve. So, applying Mediocrity, civilizations should have been commonplace across the universe for the last four billion years or so.

Therefore we are still deep in the Fermi Paradox. Either the Earth is special or there should be traces of alien civilizations.

However, it is worth noting that four billion years for the evolution of intelligent life from the first tentative self-replicating molecules is a very long time even by geological deep-time standards. So I intend now to focus in on how intelligent life evolves. The human body appeared before the modern human mind so let’s start with that and ask what are the physical characteristics that have to evolve for the evolution of an intelligent mind? To do this we take at human beings as a typical example, applying the Principle of Mediocrity.

An organism must be complex and sophisticated to have the necessary cell line specialization for a central nervous system (CNS). Multicellularity appears to be a highly likely evolutionary outcome so the conclusion must be that complex life is commonplace in the universe.

The second key factor is size. The size of an organism's CNS is directly proportional to the size of the body it controls. Modern humans have a brain that is slightly bigger than body size would suggest but not by much. In fact, statistically adult humans do not have an unusually large brain. A large-enough brain is a prerequisite for intelligence but does not guarantee intelligence and, once the minimum threshold brain size is reached, brain size not an indicator of intelligence.

For example, men have statistically significantly larger bodies than women so have larger brains. Any man who publicly concludes from this that men are more intelligent than women has just demonstrated the falsity of his hypothesis – and I hope he gets good treatment in whatever hospital they incarcerate his bloody remains. Once the critical minimum size-threshold has been reached, intelligence depends on architecture and physiology.

Large organisms evolved repeatedly on Earth so it would seem to be a commonplace product of multicellularity. Hence we may predict that large animals are commonplace across the Universe.

Humans have key characteristics other than size. We are tetrapods that are obligatory bipeds so we had the possibility to evolve hands. This is unique among mammals and reflects our unusual evolutionary journey from the trees to the plains of Africa. This change of habitat is somewhat unusual and seems to have been driven by climate instability causing rapid retreat and advance of woodland.

We have forward facing "predator" eyes, our primary sense is sight, and good hand-eye coordination – again an evolutionary hangover from an earlier arboreal existence.

Most mammals are primarily smell and sound orientated but vision is our primary sense and we use sound near exclusively to communicate, our secondary method being visual. We can make a wide variety of noises so can exchange sophisticated abstract concepts. None of this guarantees intelligence. It merely allows it to develop. For example, birds have many of these features, a sophisticated high-energy metabolism, good vision and complex vocal and visual communication but they are small, having lost out in the competition with mammals to exploit large-body ecological niches. Large non-flying birds did evolve on isolated islands but had no potential for the evolution of hands. Wings are so specialised that it is difficult to see how they could evolve into hands. Evolution is difficult to reverse.

Therapod dinosaurs, birds' close relatives, developed all the physical bodily prerequisites for the evolution of intelligence since they had bird-like characteristics but, being non-flying, could be large and had the potential for the evolution of hands. Feathers did not evolve for flight but as a component of a high-energy sophisticated metabolism and a number of therapods were feathered. So why did an intelligent therapod not evolve?

It seems self-evident to the layman that intelligence, human-level intelligence, is an evolutionary advantage that increases a species’ survivability but actually that is not true. In general, overspecialization is never a long term advantage and intelligence in particular carries severe penalties with no increase in the probability of survivability.

Intelligent brains consume ridiculous amounts of energy. Our babies are born unformed because of the strain placed on our reproductive system by a large head. An adult human might not have an unusually large brain for its body-size but a baby does. Any more than one baby at a time is therefore likely to result in the death of the children and mother so we have a low reproductive rate. Even so, we still have a high death rate for mother and baby in natural birth. Our babies are born helpless and require lengthy parental care before they can survive independently. We also suffer from mental illness. As an aside, it is intriguing that high creativity correlates with maniac-depression illnesses.

Given all these disadvantages, it is not surprising that it takes time before circumstances favour the evolution of intelligence – but time is that something large animals just don't have too much of. Wide geographic distribution and large numbers of individuals offer a buffer against extinction. Small animals have these characteristics, not large ones, so large animals are more vulnerable to random extinction. Statistically, this means that large organisms have a shorter survival span as a species.

Feathered therapods (indicative of sophisticated physiology) appeared in the Cretaceous Period, and possibly as far back as the middle Jurassic so sophisticated therapods were around for about 50 to a hundred million years so, again, why no intelligent therapod?

What kick-started intelligence in humans? Given that our powerful brains have so many disadvantages and not much payback in terms of survival, at least in the early stages before technology, why was increasing brain power been selected for, generation by generation, until the evolution of the human mind?

The primary selection pressure is survival but the second is reproductive success: Darwin pointed this out in the Origin of Species. Complex animals reproduce sexually so success involves mating. Vertebrates have complex signalling systems and behavior to persuade another individual to choose them as a suitable partner. This can result in the evolution of anatomical features that are neutral or even disadvantageous to survival. For example, the growth of antlers in deer have a high metabolic cost, offer little survival advantage, but are essential for a male deer to intimidate competitors to win the hooves of fair deer maidens.

The more complicated an organism's reproductive system the more likely the sexes of a species are to have different reproductive strategies, and the mammalian system is very complicated. The best explanation of human intelligence is that it is the result of sexual selection by women. Men tend to be attracted to women who are fit, healthy, young and not yet pregnant (slim waist).

These characteristics are not unimportant to women (well, except the last) but women get stuck with the baby so, given that people are social animals, women are attracted to high status men who will be able to provide support for them and their children. In a social animal, high status revolves around sophisticated interaction, for which intelligence is an advantage because of the need to manipulate, and enjoy good relations with, other members of society.

Even our verbal facility is probably the result of female sexual selection. In British English, boys attempt to "chat up" girls at parties. If women kept selecting for intelligence in men then this would overcome any counter-survival effect of "wasting" resources on high energy brains.

But note that the exact choice of a sexual selection feature is a haphazard process. Women might have selected on developing an oversized red nose, the ability to hop around in a circle with effortless grace, or antlers. Female birds often select on feather coloration patterns and there is evidence that therapod dinosaurs had similar behavior. Bipedal therapods were mostly predators, like wolves or tigers, whereas we are social omnivores and that is probably the key difference.

The take home message is that intelligence is a rather unlikely end result that depends on a conjunction of haphazard ecological and evolutionary features.

Maybe an intelligent species of social therapod dinosaur might still have evolved if the Cretaceous Great extinction had not happened — but major catastrophes from local events up to mass extinctions are a regular feature of life on Earth.

Species survival over time, particularly for a large organism, is to a large extent a matter of sheer luck. We almost didn't make it. About seventy-five-thousand years ago there was a catastrophe, the Toba super-volcanic eruption. The Toba Event seems to have taken human beings to the very brink of extinction. Genetic evidence suggests that we were reduced to between one and ten thousand breeding pairs. All modern humans are genetically closely related, which is why inbreeding is so very dangerous for us.

Toba was a volcanic pinprick compared to the Deccan Traps associated with the Cretaceous great extinction, or the Siberian Traps with the larger Permian extinctions, but it was enough to nearly do for a large animal geographically restricted to Africa. Toba may even have given the kick needed to evolve the human mind and civilization, but our survival was touch and go.

And here, I think, is the explanation for the Fermi Paradox. There does not need to be anything special about Earth or H. sapiens. Applying the Principle of Mediocrity, the universe probably teems with life, quite complex life. But intelligent life is simply unlikely because the evolutionary dice are rigged against it. It is very unlikely that a large complex animal, with the right sexual selection system, will survive long enough for circumstances to kick start the path to a technological civilization.

You don't need a special, unique planet to evolve an intelligent organism. You just need a lot of life on a lot of planets and one or two will win the lottery no matter how unlikely the probability. It's just a matter of random luck. There is nothing special about someone who wins the national lottery.

I suspect it is the "probability of evolving intelligent life" that is the key variable that governs the Drake Equation: the probability must be close to zero. Should we survive long enough to break free of our solar system cradle, the last variable, I suspect we will find life in abundance but will probably never ever meet intellectual peers.

It's going to be lonely out there.



The End


Copyright © 2011 by John Lamshead