30th
…an observation selection effect is operating to filter the evidence we can have about the success of our own evolutionary development.
Suppose it were true that on 99.9% of all planets where life emerged, it went extinct before developing to the point where intelligent observers could begin to ponder their origin. If this were the case, what should we expect to observe?
Answer: something similar to what we do in fact observe. Clearly, the hypothesis that the odds of intelligent life developing on a given planet are low does not predict that we should find ourselves on a planet where life went extinct at an early stage. Instead, it predicts that we should find ourselves on a planet where intelligent life evolved, even if such planets constitute a very small fraction of all planets where primitive life evolved.
The long track record of life’s success in our evolutionary past, which one may naively take to support the hypothesis that life’s prospects are in general good and that there is something approaching inevitability in the rise of higher organisms from simple replicators, turns out, after reflecting on the overwhelming observation selection effect filtering the possible evidence we could have, not to offer any such support at all, because this is the very same evidence that we should expect to have had if the optimistic hypothesis were false.
A much more careful examination of the details of our evolutionary history would be needed to circumvent this selection effect.
