Re: A Sample of...One
I think there's "life" out there, in the sense of self-replicating information-carrying structures (like DNA or RNA but potentially different).
Of course, microbes are much more likely than macroorganisms (given Earth's history of life and their relative prevalence). And vegetative macroorganisms are probably much more likely than animal-like ones. And dumb alien animals are more likely than intelligent ones. And so on, with intelligent enough to communicate less likely, intelligent enough to develop complex technology, intra-solar-system space travel, interstellar travel, intergalactic travel, etc. etc.
For intelligent life also needs to have managed not to destroy itself, and given human history, it seems like developing a general intelligence can be such a strong adaptive advantage (the ability to outsmart disease, exploit non-obvious resources, develop weapons that aid in hunting and largely eliminate the threat of predators, etc.) that it leads to population growth that will consume the planet's resources and create conflict, etc. long before they develop the means for interstellar travel and colonization. The idea of Vulcans is nice, but given what we know about evolution, doesn't it seem only logical that the illogical and selfish Vulcan ancestors might've reproduced more? It could be that technological civilizations tend not to survive very long. It could be that there have been thousands or millions of advanced (i.e. to human level technology) civilizations in the universe... and also that >99% of them are long gone.
And given that a planet has life, it isn't guaranteed to be easily discoverable. Evolution is powerful but there are still areas of Earth that are devoid of life. It could be that it's on a planet with a frozen surface and the life is in the oceans beneath. Or it could be that the life is deep down where there is geothermal heat. It could be that life once covered the planet, but massive changes to the planet, climate changes or asteroid strikes or the like have killed most of it. Maybe eventually the remaining/existing life will adapt to colonize the rest of the planet, but that could be millions and millions of years from now.
It's also possible there could be lifeforms we wouldn't even recognize as life (at least, not for a long time) even if they fell into our laps.
But how likely is it to be near enough to us that we can discover it directly? Given how much effort it has been to explore our own backyard... While unlikely, it could be there are or were microbes on Mars but we haven't even explored the areas of Mars with significant amounts of water. But imagine that there are microbes on a planet in one of the 1,000 closest solar systems (all of which are light-years from ours!) - which would already be a pretty lucky occurrence. How long would it take us to explore those solar systems, to be able to travel to the planet, and to discover the existence of microbes on the surface? And then think of how much rarer life intelligent enough to have developed language and civilization would be.
I think the possibility of some sort of life, and even intelligent life, elsewhere in the universe is pretty high. Especially if we also allow that it could've existed in the past but be dead now. But the likelihood we'll ever encounter any of it, much less advanced spacefaring civilizations that we would want to meet (because given human history of uncontacted peoples, being contacted seems highly likely to be disastrous* even if the aliens don't just immediately declare war on us), seems extremely low to nonexistent.
*On the other hand, one could propose that species that behave in a warlike/oppressively colonial manner would be less likely to develop to the point of being able to visit Earth, since they may be more likely to destroy themselves through infighting and resource mismanagement. In other words, the Klingons would've been too busy nuking each other to get to the point where they could make contact with humans, while the Vulcans wouldn't. On the other other hand, it could also be that they would be a species that's developed a more eusocial way of being and their high-level of intraspecies peacefulness has little to no bearing on how they'd treat humans. And on the fourth hand, organisms vary! Even if the Vulcans as a whole were peaceful on planet Vulcan in the period immediately preceding their development of easy interstellar travel, there's no guarantee that Vulcan colonists would be so or remain so since the survival pressures would be very different and it would probably be a very non-representative sample of Vulcans who would choose to leave the homeworld.
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