Which criterion is NOT used to define a species?

Biochemical diversity is not typically used as a defining criterion for a species in the same way that morphological similarity, interbreeding capability, and a common gene pool are.

Morphological similarity refers to the physical characteristics that organisms share, which can help in identifying and classifying species based on observable traits. Interbreeding capability is a crucial factor in species definition, particularly in the biological species concept, as it emphasizes the ability of individuals to reproduce successfully and produce viable offspring. A common gene pool also ties into the idea of species, as it suggests that members of a species share a set of genes that facilitate reproduction and the continuation of the species.

While biochemical diversity can indicate genetic variation or potential evolutionary divergence, it does not inherently define a species. Instead, it reflects the differences within or between populations, which could lead to the emergence of new species but is not a primary criterion used to identify a species itself.