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Flight has evolved separately several different times in the history of life on earth — insects, birds and mammals have all taken to the skies, and each class evolved the ability independently of one another.  Eyes have evolved several different times over the history of life on earth.  The jellyfish developed camera eyes not unlike the human eye, despite the fact that our two species are separated from one another genetically by some 600 million years.

But exactly how common is… intelligence?

It is a trait that seems to have evolved only once in the four billion year history of life on earth.  Like photosynthesis or like the evolution of the eukaryotic cell, intelligence seems to be an outlier, a wonderful spelling error in the recipe that changed something less tasty into the cookie.  And certainly, “intelligent life” is open to interpretation… chimps & apes, dogs, dolphins, elephants, crows and the aforementioned jellyfish all share intelligence, even down to the ability to manipulate tools.  And if an extraterrestrial were to come to earth judging on the curve, even our degree of intelligence might not impress.

But let us for a moment reconsider the question to focus on a species that is capable of a technological society.  In four billion years of life (and four and-a-half billion years of the earth’s existence) a species with an intelligence capable of producing a technological society has arisen only once.  Homo sapiens emerged out of the tangled tapestry of earlier Homo lines some 200,000 years ago, .005% of the history of life on this planet, or .0044% of the planet’s existence.  By any interpretation this is a fluke — it’s like throwing down a royal flush; it wouldn’t happen the first time you throw down the cards, but if you’re tossing down cards often enough the odds demand that eventually a perfect hand will come down… even if it does take four billion-plus years.

If a technological-capable species has existed on this planet for only a fraction-of-a-fraction of its existence, here’s the big question as we send out signals and carefully listen for reply from giant radio-telescopes… exactly how likely is it that we might find intelligence elsewhere?  Make no mistake, the building blocks for water-based life such as we find on earth seem everywhere in the universe.  Simple amino acids and water are found in abundance in asteroids and comets — and what are all rocky planets but accretions of these same asteroids and comets?  Comets and asteroids whiz around planetary systems like prepackaged freeze-dried, life-delivery kits!  But if it took three billion years for the eukaryote to evolve on earth; if it took four billion years for complex life to find its footing; if it took four and-a-half billion years for intelligent life to evolve and ponder life elsewhere… then finding intelligent life in the universe is a different measure entirely.  As NOVA’s 2014 episode entitled “Alien Planets Revealed” suggested:  “The probability of intelligent life evolving on another planet is perhaps the greatest unanswered question.  But there are hints on earth that intelligence might be the exception, not the rule.”

 Sharks… have ruled the seas for 400 million years, and yet their brains are no larger than peas.  How could it be that after 400 million years sharks have not developed a higher intelligence?…  That tells us something frightening about life elsewhere in the universe:  perhaps the intelligence of which we humans are so proud is not an attribute that is strongly favored in Darwinian evolution.

– Geoff Marcy (http://www.pbs.org/wgbh/nova/space/alien-planets-revealed.html)

And considering an intelligence capable of a technological civilization lengthens those odds considerably.  Just as no human is born an adult, we did not emerge as a species technologically aware.  We used tools from the beginning, but so did our ancestors millions of years ago, so at what point did we actually become a “technological species”?  This is certainly an elastic term open to interpretation, but let’s say for the sake of generosity that we’ve been technological since the invention of writing, some 4,500 – 5,000 years.  This also coincides with many of our early megalithic and monolithic structures, so this seems fair, if not overly kind.  By this metric, the planet earth has possessed an intelligent species capable of technological understanding for one one-millionth of the planet’s existence.  Let me stress than again.  One one-millionth — that’s equivalent to one second in 11 and-a-half days.  It’s like a lifelong shut-in across the street opening his blinds and peering outside for 42 minutes in his 80-year life.

Now apply the same metric to another technological society in the galaxy.  What is the likelihood of two 80-year old hermits (whose lives don’t even necessarily coincide!) peering out the window and spotting one another in the same 42 minute overlap?

But the likelihood would increase if there were more than two.  Since the Kepler telescope began finding exoplanets in 2009, estimates of habitable planets in the galaxy have reached from the stratosphere into the airless region of hyperbole, but if one were to consider a rather conservative estimate and begin building a template from that, let’s say that there are 10 billion habitable planets in our galaxy — and to be clear, “habitable” should not be confused with “inhabited,” the former means capable of hosting life, but not necessarily inhabited.  So imagine 10 billion habitable planets, and let’s just say for argument’s sake that those 10 billion aren’t quite as habitable as we thought at first flush and maybe only one out of ten actually does harbor life.  Now if even just 1 in 10 hosts life that would still be one billion inhabited planets in the galaxy.

But as we’ve seen it takes time to evolve intelligence; on earth it took four and-a-half billion years.  Factor in the same metric for a technological society as we’ve seen on earth and that means that only one one-millionth of a planet’s existence might see a species capable of technological advancements and capable of understanding communication.  So essentially, there’s a one-in-a-million chance of an inhabited (similarly-aged) world possessing a technological society right now.  That’s right, we have to divide our number by one million.  This winnows the field from one billion to 1000.

But not all planets are the same age; some in the Milky Way are older, but many are younger, and this is likely to further reduce the number.  One must also consider the idea that some intelligent species might exist on “water worlds” or never have left the water as life on earth eventually did, which means its society would be unable to take advantage of any “technology” as we would recognize it.

Other considerations:

  • Exactly how common is an over-sized moon like ours that was so crucial in stabilizing the earth’s tilt, allowing for long-term climate stability?
  • How common is photosynthesis, a necessary precursor for the production of free oxygen, itself a necessary precursor for complex, multi-cellular life?
  • How common is a churning-iron core fueling a magnetic field and plate tectonics?
  • And here’s perhaps the biggest one…  How common is it that water-based life actually leaves water?

All of the above are crucial thresholds, without any of which you would not be reading this.  What are we down to now… 100?  200?  Generously!

But even with such a low estimate of 200 technological civilizations spaced around the Milky Way galaxy right now, the same result dictates that in the larger observable universe there would still be some 40 trillion civilizations at this moment.  Forty trillion, right now.

Still, even if we could bridge the boundaries of physics and talk to them… well, could we really?

 We don’t have conversations with any other species on earth, with whom we have DNA in common!  To believe that some intelligent other species is going to be interested in us, enough to have a conversation…?  ‘Isn’t that quaint…!’

– Neil Degrasse Tyson (https://www.youtube.com/watch?v=K2wp5Qe3JV0)

I know, kind of a bummer to end with, but listen… chimps are between 96% and 98% genetically identical to us, and we can’t even achieve meaningful conversations with our closest existing relatives.  If we are unable to have a significant conversation with any other species on earth — and we’re related to them — then what would suggest a conversation is even possible with some species that is completely unrelated to us?