 Leigh Van Valen proposed the hypothesis as an "explanatory tangent" to explain the "Law of Extinction" (known as Van Valen's law), which states that the probability of extinction does not depend on the lifetime of the species (or higher-rank taxon), instead being constant over millions of years for any given taxon.However, the probability of extinction is strongly related to adaptive zones, because different taxa have different probabilities of extinction.In other words, extinction occurs randomly with respect to age but nonrandomly with respect to ecology.