Clearly the best evidence for other advanced life being too rare and/or too far away is the fact we haven't heard from them yet.
But, I hesitate to make all those other assumptions about no liquid water and this kind of solar system vs that kind of solar system because we have only seen a sample size of one solar system. Only recently have we started to obtain data on other solar systems.
And, the rate of advance of our scientific discoveries and technologies has been logarithmic. So who's to say in the future we won't find animals or at least evidence of animal life in nearby solar systems?
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