If correct, the theory of the existence of discrete species, each with its own essence, brings biology closer to the physical sciences.

Such analyses can suffer from polymorphisms within a species, the existence of cryptic species and the frequent lack of distinct morphological characters amongst females.

Some studies have revealed the existence of numerous cryptic species and have contributed to taxonomic expansion of the group.

In light of this work and the known existence of cryptic species, it is important to characterise isolates used to develop biological insecticides.

Similar processes would explain anomalies such as the existence of closely related species in widely separated locations.

He further argued that variation, far from being problematic, actually provides the explanation for the existence of distinct species.

The widespread breeding and distribution of hybrids could threaten the existence of both pure species and subspecies of the ecosystem.

Various populations of rare fern exist, although the impact of 19th century collectors threatened the existence of several species.

The effect of the ecological footprint of our species is to prevent the continuing existence of certain other species in the planetary ecosystem.

The existence of cryptic species suggests that neither the number of symbionts nor their evolutionary relationships are necessarily fixed ecologically.