Inductive probabilities in astrobiology and SETI: Have sceptics retreated?

Abstract

The alleged improbability of particular critical steps has for quite a long time been one of the favoured arguments of the opponents of universal, cosmic evolution. In a nutshell, the argument goes like this: various realms in which we perceive evolutionary processes are separate domains (implicitly endowed with separate conceptual ‘essences’), since the transition, probabilities between these domains are astronomically small numbers, of the order of 10−100 or smaller. For instance, we should discuss chemical and biological evolution separately, since the probability of spontaneous transition between these two domains – the origin of life or abiogenesis – is extremely small; we are dealing with, in Monod’s famous words, ‘a lucky accident’. Analogous arguments are made for transition between simple microscopic life and complex metazoans, or for transition between conventional animals and intelligent beings with language and culture. These arguments are often behind either creationist or ‘rare-Earth’ argument for uniqueness of our astronomical habitat, as well as behind the scepticism towards astrobiology and SETI studies. The probabilities cited are usually inductive inferences from the prima facie requirements deemed historically necessary in the unique terrestrial case. In the last couple of decades, however, we have obtained much better insight into the dynamical processes underlying some of these requirements – and original ideas emerged as to how we could bypass at least some of them. In that light, it is interesting to consider whether this sea change influenced the sceptical discourse; as I will show, there are reasons to conclude that this kind of scepticism is motivated by extrascientific concerns.