It has often been said that, if the human species fails to make a go
of it here on Earth, some other species will take over the running. In
the sense of developing high intelligence this is not correct. We
have, or soon will have, exhausted the necessary physical
prerequisites so far as this planet is concerned. With coal gone, oil
gone, high-grade metallic ores gone, no species however competent can
make the long climb from primitive conditions to high-level
technology. This is a one-shot affair. If we fail, this planetary
system fails so far as intelligence is concerned. The same will be
true of other planetary systems. On each of them there will be one
chance, and one chance only. (Hoyle, 1964)