Are we alone within the universe? It comes down as to if intelligence is a possible final result of pure choice, or an inconceivable fluke. By definition, possible occasions happen incessantly, inconceivable occasions happen not often—or as soon as. Our evolutionary historical past exhibits that many key variations—not simply intelligence, however advanced animals, advanced cells, photosynthesis, and life itself—had been distinctive, one-off occasions, and subsequently extremely inconceivable. Our evolution could have been like successful the lottery…solely far much less probably.
The universe is astonishingly huge. The Milky Approach has greater than 100 billion stars, and there are over a trillion galaxies within the seen universe, the tiny fraction of the universe we will see. Even when liveable worlds are uncommon, their sheer quantity—there are as many planets as stars, possibly extra—suggests a number of life is on the market. So the place is everybody? That is the Fermi paradox. The universe is massive, and outdated, with time and room for intelligence to evolve, however there’s no proof of it.
May intelligence merely be unlikely to evolve? Sadly, we will’t research extraterrestrial life to reply this query. However we will research some 4.5 billion years of Earth’s historical past, the place evolution repeats itself, or doesn’t.
Evolution typically repeats, with completely different species independently converging on related outcomes. If evolution incessantly repeats itself, then our evolution could be possible, even inevitable.
And putting examples of convergent evolution do exist. Australia’s extinct, marsupial thylacine had a kangaroo-like pouch however in any other case appeared like a wolf, regardless of evolving from a unique mammal lineage. There are additionally marsupial moles, marsupial anteaters, and marsupial flying squirrels. Remarkably, Australia’s whole evolutionary historical past, with mammals diversifying after the dinosaur extinction, parallels different continents.
Different putting instances of convergence embrace dolphins and extinct ichthyosaurs, which developed related shapes to glide via the water, and birds, bats, and pterosaurs, which convergently developed flight.
We additionally see convergence in particular person organs. Eyes developed not simply in vertebrates, however in arthropods, octopi, worms, and jellyfish. Vertebrates, arthropods, octopi, and worms independently invented jaws. Legs developed convergently within the arthropods, octopi, and 4 sorts of fish (tetrapods, frogfish, skates, mudskippers).
Right here’s the catch. All this convergence occurred inside one lineage, the Eumetazoa. Eumetazoans are advanced animals with symmetry, mouths, guts, muscle groups, a nervous system. Totally different eumetazoans developed related options to related issues, however the advanced physique plan that made all of it doable is exclusive. Complicated animals developed as soon as in life’s historical past, suggesting they’re inconceivable.
Surprisingly, many vital occasions in our evolutionary historical past are distinctive and, in all probability, inconceivable. One is the bony skeleton of vertebrates, which let massive animals transfer onto land. The advanced, eukaryotic cells that each one animals and vegetation are constructed from, containing nuclei and mitochondria, developed solely as soon as. Intercourse developed simply as soon as. Photosynthesis, which elevated the power accessible to life and produced oxygen, is a one-off. For that matter, so is human-level intelligence. There are marsupial wolves and moles, however no marsupial people.
There are locations the place evolution repeats, and locations the place it doesn’t. If we solely search for convergence, it creates affirmation bias. Convergence appears to be the rule, and our evolution seems to be possible. However if you search for non-convergence, it’s all over the place, and critically, advanced variations appear to be the least repeatable, and subsequently inconceivable.
What’s extra, these occasions relied on each other. People couldn’t evolve till fish developed bones that permit them crawl onto land. Bones couldn’t evolve till advanced animals appeared. Complicated animals wanted advanced cells, and sophisticated cells wanted oxygen, made by photosynthesis. None of this occurs with out the evolution of life, a singular occasion amongst singular occasions. All organisms come from a single ancestor; so far as we will inform, life solely occurred as soon as.
Curiously, all this takes a surprisingly very long time. Photosynthesis developed 1.5 billion years after the Earth’s formation, advanced cells after 2.7 billion years, advanced animals after 4 billion years, and human intelligence 4.5 billion years after the Earth shaped. That these improvements are so helpful however took so lengthy to evolve implies that they’re exceedingly inconceivable.
An Unlikely Sequence of Occasions
These one-off improvements, vital flukes, could create a sequence of evolutionary bottlenecks or filters. If that’s the case, our evolution wasn’t like successful the lottery. It was like successful the lottery once more, and once more, and once more. On different worlds, these vital variations may need developed too late for intelligence to emerge earlier than their suns went nova, or in no way.
Think about that intelligence will depend on a sequence of seven unlikely improvements—the origin of life, photosynthesis, advanced cells, intercourse, advanced animals, skeletons, and intelligence itself—every with a ten % probability of evolving. The percentages of evolving intelligence grow to be one in 10 million.
However advanced variations could be even much less probably. Photosynthesis required a collection of variations in proteins, pigments, and membranes. Eumetazoan animals required a number of anatomical improvements (nerves, muscle groups, mouths, and so forth). So possibly every of those seven key improvements evolve simply 1 % of the time. If that’s the case, intelligence will evolve on simply 1 in 100 trillion liveable worlds. If liveable worlds are uncommon, then we could be the one clever life within the galaxy, and even the seen universe.
And but, we’re right here. That should rely for one thing, proper? If evolution will get fortunate one in 100 trillion instances, what are the percentages we occur to be on a planet the place it occurred? Really, the percentages of being on that inconceivable world are one hundred pc, as a result of we couldn’t have this dialog on a world the place photosynthesis, advanced cells, or animals didn’t evolve. That’s the anthropic precept: Earth’s historical past should have allowed clever life to evolve, or we wouldn’t be right here to ponder it.
Intelligence appears to rely upon a sequence of inconceivable occasions. However given the huge variety of planets, then like an infinite variety of monkeys pounding on an infinite variety of typewriters to put in writing Hamlet, it’s certain to evolve someplace. The inconceivable end result was us.