With countless planets and stars in the universe, it is beyond any reasonable doubt that life is not restricted to our world. This is the only certainty about extraterrestrial life, everything else rests somewhere between well founded scientific speculation and pure schizophrenia.
Life on Earth seems to have appeared as soon as the planet developed adequate physical-chemical conditions to host large organic molecules: enough energy available to activate chemical reactions, but not so much that would quickly destroy the products.
From this standpoint, it is fair to suppose that life is a common phenomenon. Just a natural followup of the increasing chemical complexity occurring in a system fed by an external energy source, like a sun or a geothermal hot spot. The elusive threshold between a chemical inanimate complex and the simplest living being is just the capacity of replicating itself. From then on, only evolution matters.
After having life, the evolutionary way progressing towards intelligent beings curious about the universe should be more or less straightforward, no?
Not necessarily. I would say that is very likely that we can find simple life forms like virus in every warm and wet hole in the galaxy. To believe, however, that life aims at intelligence is just anthropocentric silliness.
People believing that we may find other intelligent beings out there use to appeal to an statistical reasoning: with so many planets in the universe, intelligence must have emerged somewhere. They dream of f i = 1 in the Drake equation.
But we can use the statistical reasoning to argue for the opposing view as well: we have today over 8 million species in our planet. From those, maybe only one hundred, among rodents, birds, fishes, octopus, whales and primates, show some degree of culture accumulation, in the sense of behavioral patterns that are not genetically encoded, but are spontaneously invented or copied. And only two of them, modern humans and neanderthals, ever showed complex levels of cultural accumulation.
Moreover, take also into account that from the 3.8 billion years since life first appeared and the 2 million years of human natural history, complex cultural activities have been important for only 50 thousand years.
Thus, not so good statistically. In this light, emergence of intelligent life in our planet looks less a necessity of evolution, and more a singularity. A rare accident, which does not need to occur in other living worlds. I will return to this point in a next post.
It is disappointing, but f i may be really near zero. Although I sympathise with SETI people and see greatness in their search for extraterrestrial intelligence, it is much likely, we are alone on our small warm rock in the middle of an oppressively mute universe.
At least this may be one more reason for us to take better care of each other.
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