A simple thought experiment suggests that humans are earth-life’s best bet. In this experiment there are three key factors: the probability that humans can avoid extinction and transcend oblivion; the probability that new intelligent life would re-evolve if humans became extinct; and the probability that a newly evolved intelligent species could avoid its own extinction and transcend oblivion, assuming there is enough time to do so. To favour extinction of humans, the product of the second and third probabilities must be greater than the first probability.

Bruce Tonn, ‘Futures Sustainability’, Futures, vol. 39, no. 9 (November, 2007), p. 1100