In theory, a number of different explanations could account for a singularity. Schematically, I distinguish seven different, not necessarily mutually exclusive kinds. Represented schematically in Figure I.1 (printed on the front endpaper of this book), these different kinds of singularities are, in the order of decreasing probability:

Mechanism 1. Deterministic Necessity. According to this interpretation, things could not have been otherwise, given the physical–chemical conditions that existed. Most physical and chemical phenomena belong to this category. They obey the laws of nature in a strictly reproducible fashion. Only at the subatomic level does quantum mechanics allow for some uncertainty. Life is not affected by events at that level, except, according to a theory proposed by some investigators but far from unanimously accepted, in the brain–mind connection.

Mechanism 2. Selective Bottleneck. This mechanism applies to any situation where different options are subject to an externally imposed selection process that allows only a single one to subsist. The most familiar such situation occurs in Darwinian natural selection, where different organisms compete for available resources within ecosystems and the organism most apt to survive and reproduce under prevailing environmental conditions ends up predominating. Many other instances of a basically similar process are encountered or can be created, depending on the nature of the competing entities and on that of the selection criteria.