Human intelligence is a peacock feather

In the 1950’s, physicist Enrico Fermi asked a seemingly innocuous question over lunch, “Where is everyone?” Those present immediately understood he wasn’t talking about anyone being missing from the dining room. Fermi was referring to aliens. Fermi wanted to know, why don’t we see evidence for intelligent extraterrestrial beings when we look out into space?

Why would there be intelligent life in outer space?

The universe is both astonishingly big and surprisingly transparent. We can look into the dark night sky and see light from 13.8 billion years in the past, showing us the emerging structure of the cosmos in remarkable detail. The sheer size and scale of the universe is beyond comprehension, with roughly two hundred billion galaxies in the visible universe, containing upwards of 10^29 stars, that’s 100,000,000,000,000,000,000,000,000,000 stars.

To think we are alone in the universe stretches the bounds of credulity, especially when we consider some of the complex molecules we’ve found forming naturally in deep space. The Sagittarius B molecular cloud, as an example, contains billions of gallons of alcohol in the form of C2H4O, and copious amounts of at least one of the amino acids coded by DNA, glycine—CH2NH2COOH, along with various simple sugars. It seems ET is boozy and has a sweet tooth.

Space is a chemical factory. There are over five hundred different types of amino acid. Life on Earth uses just twenty. To our surprise, we’ve found meteorites containing seventy-five different amino acids, although only ten of these are used in biology.

Laboratory tests simulating the environment of space, have shown that these acids can naturally link to form chains, marking the beginning of the complex chemistry that underpins life on Earth.

Sagittarius B

Sagittarius B molecular cloud. Picture credit: dailygalaxy

When you consider that the Sagittarius B molecular cloud contains enough material to form three million stars like the Sun, each with its own unique planetary system, you realize life may be far more common than we suspect. There are literally millions of opportunities for life to form.

So if the lego building blocks for life are abundant in space, and if life arises naturally elsewhere in the universe, where is everyone? This is precisely the question that perplexed Fermi.

Once an intelligent species ventures into space, it should naturally branch out to explore the galaxy in much the same way Europeans spread throughout Earth once they mastered sailing. Given the immense age of the universe, and given how relatively quickly we should be able to populate the galaxy once we get going, Fermi’s question is a paradox—Where is everyone? There should be dozens, hundreds, perhaps thousands of other intelligent space-faring alien species out there, but there’s only silence.

Common solutions to Fermi’s Paradox

There are at least fifty potential answers to Fermi’s Paradox but here are the top ten.

  1. Hospitable planets like Earth are extremely rare and we are the first species to make it into space.
  2. Aliens are everywhere, but we can’t detect them because their communication is point-to-point and highly efficient.
  3. There’s a Great Filter, something that blocks progress to the stars so very few civilizations expand into space.
  4. Interstellar travel is too costly and too time consuming to undertake. Although under this scenario, we should still be able to detect other space-faring species.
  5. Earth is in a nature preserve, being deliberately isolated until we develop into a peaceful star-faring species. This is the Star Trek Prime Directive, although both isolating us and deliberately hiding all knowledge of other galactic civilizations seems unrealistically complex to be practical.
  6. Aliens keep to themselves. Either they’re not interested in exploration or they’re weary of provoking other more hostile aliens to attack. After all, it’s not smart to shout in a jungle.
  7. ET has transcended physical form and escaped mortality by living in virtual reality in a computer server farm on the edge of the galaxy.
  8. Forget ET, we’re living in a virtual reality similar to the Matrix so space isn’t real.
  9. We are ET. The movie Prometheus explores this possibility, but as life has evolved for at least 3.6 billion years on Earth, for this premise to hold, ET would have to be a very primitive microbe that encountered Earth billions of years ago.
  10. Aliens are already among us but keeping their presence secret. Although this is a popular notion it’s highly unlikely.
Seti @ Home

Picture credit: Seti @ Home

Great Filter

The Great Filter addresses Fermi’s Paradox by suggesting life might be common throughout the universe, but it may have a torturous, hazardous path to the stars.

Looking at our own history, we can seen numerous gates/checkpoints life had to pass through before Homo sapiens arose.

For billions of years, life on Earth consisted of nothing more than microbes. It took an absurd amount of time for life to make the jump from single-celled organisms to multicellular plants and animals. What if that was a fluke?

There’s been dozens of mass extinction events that could have obliterated life on Earth, but somehow life survived. And if an asteroid hadn’t wiped out most of the dinosaurs roughly 65 million years ago, mammals may never have diversified into their current forms.

When considering the Great Filter, one question that arises is—which side of the filter are we on?

Even now, there’s no guarantee we’ll make it to the stars. Any number of possible doomsday scenarios may yet play out, from nuclear war to the rise of a terminator-like artificial intelligence, or an engineered disease. Any of these may drive us to extinction. We could still be filtered out of the celestial equation. Even such promising advances as nanotechnology could ultimately be our undoing.

If the Great Filter that has held back interstellar colonization for others was the leap from single to multicellular life, we’ve already made it, as we are well beyond that. If the Filter turns out to be our own warring, self-destructive nature, we may not make it to the stars. Stephen Hawking goes so far as to say, “Our only chance of long-term survival is not to remain inward-looking on planet Earth, but to spread out into space.


Fermi’s Paradox has one critical, underlying assumption—intelligence will arise naturally elsewhere in the universe. But what if this assumption is wrong?

What does it take for intelligence to flourish?

Although life may thrive on thousands, perhaps millions of other planets throughout the universe, a closer look at the evolution of intelligence on Earth suggests the Great Filter may be more of a Great Brick Wall. Intelligence is not a default for evolution.

Natural selection is the winnowing process by which organisms have adapted to life on Earth. Too many seeds fall, too many puppies are born, and too many microbes divide for them all to survive in the long term.

E. Coli, as an example, doubles every 20 minutes. If it could E. Coli would cover the entire planet in a day and a half. By the end of two days, E. Coli would weigh considerably more than the entire planet, molten core and all. Clearly, that doesn’t happen, and the reason is E. Coli doesn’t have unlimited resources and cannot divide unchecked.

Charles Darwin’s astonishing insight in On the Origin of Species was that those bacterium, seeds or puppies that do survive, survive for a reason. If one out of a thousand seeds flourishes into a tree, the question is—why that particular seed? What allowed that seed to thrive? If it was blind luck, there’s no evolutionary advantage. But if it was because of a genetic trait, a trait that made the seed slightly lighter so it could float on the wind, or slightly thicker so it couldn’t be digested by an animal, then that trait will be passed on to the next generation, and so gradual change dominates evolution.

It’s tempting to think that intelligence is the result of natural selection, as our intelligence certainly gives us an advantage over other animals and has allowed us to dominate life on Earth, but that’s not entirely correct. Intelligence is not necessarily a survival trait.

There are varying degrees of intelligence in nature. Intelligence is found in species such as corvids and cephalopods, cetaceans and apes, but we don’t find any intelligence as advanced as our own. Why? This is an important question, as when we look at evolutionary traits that bestow advantages such as sight or flight, we see convergent evolution happening on a vast scale.

Convergent evolution describes how entirely different, seemingly unrelated species evolve similar traits, like dolphins and sharks both having dorsal fins even though sharks evolved 450 million years ago, while dolphins are mammals that returned to the sea a mere 50 million years ago.

Take sight as an example. Sight has evolved independently at least 40 different times. Being sensitive to light conveys such an overwhelming evolutionary advantage it spawned an arms race between predators and prey. As marvelous as our sight is, our vision is nothing compared to that of the Mantis shrimp that sees twelve primary colors compared to our three. The Mantis shrimp sees a broader spectrum of light than we do, and can also distinguish different types of polarized light, something we need sunglasses to detect.

The point is—sight provides such an immense evolutionary advantage, we see sight emerging throughout the animal kingdom, and in ways that dwarf our own vision. The same is true when it comes to flight, with birds, bats and insects all adopting different methods to take to the air. We don’t see this when it comes to advanced intelligence. And it’s not just that we don’t see whales as smart as us. We don’t see any other species in the Homo genus with our level of intelligence, and yet we’re sure they once existed. Think about how astonishing that is. We are the only remaining species on this branch of the evolutionary tree of life. Why? If intelligence is a survival trait, we should see dozens of other Homo species, but we don’t.

There are twenty thousand different species of butterfly. There are three hundred and fifty thousand different species of beetles. There is only one Homo species. Us. Sapiens.

If intelligence provided an evolutionary advantage, why don’t we live in a world with Homo neanderthals and Homo erectus? It’s tempting to think of neanderthals as brute cavemen, but our own ancestors weren’t faring much better at the time.

Neanderthals were highly intelligent, with a level of ingenuity and cognitive awareness well beyond that of chimps or dolphins. They had complex social structures, caring for their sick, burying their dead, working with stone tools, painting on walls, making jewelry and even playing musical instruments. Although the evidence is scant, there’s reason to consider Neanderthals were ocean faring, having established colonies on such remote islands as Crete. We still don’t fully understand why it was Homo sapiens that eventually planted a flag on the Moon and not Homo neanderthals.

Homo sapiens

Evolution of the Homo genus. Picture credit: Nova

When we consider the evolution of human intelligence, we have to think beyond ourselves. We’re simply the latest rendition of Homo, a complex genus that branched from hominids to become Homo sapiens. Roughly 4-5 million years ago, we shared a common ancestor with chimpanzees, that is to say, from that point our ancestors gradually branched out into a number of species that eventually led either to extinction or to Homo sapiens. The physical traits we have are hominid/homo traits, they’re not unique to Homo sapiens. We inherited these traits from those that came before us, including our intelligence.

If intelligence isn’t a survival trait, then what is it? How did intelligence arise?

Following on from On the Origin of Species, Charles Darwin wrote The Descent of Man, describing another often overlooked aspect of evolution—sexual selection. Like natural selection, sexual selection describes a mechanism by which species adapt, but instead of survival traits allowing an animal to reproduce, sexually desirable or sexually dominant traits allow an animal to mate. In both cases, the end result is passing successful genes onto future generations.

Natural selection is blind and indifferent, whereas sexual selection is in the eye of the beholder.

Lophorina superba is the "superb bird of paradise"

Lophorina superba is the “superb bird of paradise.” Here a male dances before a female, enticing her to mate. Picture credit: Birds of Paradise

Natural selection refines traits necessary for survival. Sexual selection doesn’t. Sexual selection is extravagant and, on occasion, can be wasteful, perhaps even detrimental when maladaptations arise.

Deer have antlers developed as the result of sexual selection, being used for fights over mates, but these can cause an untimely death when caught up on bushes. The Irish Elk may have gone extinct due to a combination of factors, from human hunting to the inability of males to negotiate wooded areas, and even the excessive nutritional demands of its antlers on its diet.

Irish Elk may have gone extinct due to the excesses of sexual selection

Irish Elk may have gone extinct due to the excesses of sexual selection: Picture credit: Christies

In the same way, peacock feathers attract pea hens while placing a burden on flight when escaping predators. Over time, this dichotomy balances out or a species goes extinct.

For millions of years, the survival of the Homo genus relied on making stone tools and harnessing fire, skill in hunting and scavenging. This dependency caused intelligence to become a desirable trait, an indicator of biological fitness. Both men and women, when selecting mates, had a natural preference for someone with a level of intelligence capable of mastering these skills. This isn’t to say geeks are sexy, but that there was a minimum level of intelligence below which prospective partners would be seen as repulsive. Once established, a positive feedback loop led to a level of intelligence far in excess of that required by hunter-gathers, bringing us music, art, literature and science, and yet the evolution of Homo sapiens was by no means guaranteed.

Intelligence came at a price. Big brains are burdensome. Whereas giraffes can walk within minutes of being born, human children take years to mature to the point of being physically independent, placing a strain on the overall survival of the species. For the rest of the Homo genus, such a development may have compounded with other pressures and led to extinction. Like peacocks struggling to flee from predators, numerous species of the Homo genus arrived at an evolutionary dead-end, unable to juggle sexually selective pressures against natural selection. Somehow, we got lucky and the advent of agriculture allowed civilization to emerge.

If the level of intelligence required to reach the stars is a sexually selected trait and not the result of natural selection, we may well be alone in the universe. If sexual selection is a requisite for advanced intelligence then the good news is, we’ve already passed through the Great Filter, but we may very well be one of only a few species to emerge among the stars. After 3.8 billion years of evolutionary development, it seems advanced intelligence isn’t natural, it’s sexual. We may well find life on other planets, but the proportion of intelligent life might be exceedingly low given how specialized intelligence is in nature.

Human intelligence is a peacock feather, an extravagant excess developed due to sexual preferences, and this may well explain why we don’t see intelligent life elsewhere in the universe as the level of intelligence required to build a rocket ship is far rarer than we ever imagined.


Peacocks are examples of sexual selection in extreme. Picture credit: 281 Photography

I’m an optimist. With all the focus NASA has on imaging distant planets, I think we’ll find life flourishing elsewhere in space within the next few decades. I’d like to think SETI will prove me wrong about advanced intelligence being exceedingly rare because of its dependence on sexual selection, but it is worth considering the concept and adding it to the discussion around Fermi’s Paradox.

4 thoughts on “Human intelligence is a peacock feather

    • It’s an interesting concept, huh? Once you become aware of it, you see sexual selection (or the lack thereof) almost everywhere, it’s a spectrum… from there being no distinction between male and female crows, to the magnificent differences between peacocks and peahens.

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