Evolutionary grade

The term was coined by British biologist Julian Huxley, to contrast with clade, a strictly phylogenetic unit.

In the early 19th century, the French naturalist Latreille was the first to divide tetrapods into the four familiar classes of amphibians, reptiles, birds, and mammals.

[3] In this system, reptiles are characterized by traits such as laying membranous or shelled eggs, having skin covered in scales or scutes, and having a 'cold-blooded' metabolism.

In Linnaean systematics, evolutionary grades are accepted in higher taxonomic ranks, though generally avoided at family level and below.

While taxonomy seeks to eliminate paraphyletic taxa, such grades are sometimes kept as formal or informal groups on the basis of their usefulness for laymen and field researchers.

[6] In bacteriology, the renaming of species or groups that turn out to be evolutionary grades is kept to a minimum to avoid misunderstanding, which in the case of pathogens could have fatal consequences.