Evolutionary grade

An evolutionary grade is a group of species at the same level of organisation.^[1]^[2]

It refers to a group of animals or plants which are very similar, but which are not a clade. They have a similar morphological or physiological complexity, and they are often adapted to the same way of life.

The term was coined by Julian Huxley, to contrast with clade, which is a strictly phylogenetic unit.^[3]^[4] The use of 'grade' as a term in biology was strongly supported by Ernst Mayr,^[5] who also pointed out that the term had been used for some time before cladism.^[6]

↑ Futuyma D.J. 1986. Evolutionary biology. 2nd ed, Sinauer. p288
↑ Futuyma D.J. 2005. Evolution. Sinauer. p84 and figure 4.17
↑ Huxley J.S. 1958. Evolutionary processes and taxonomy with special reference to grades. Uppsala Univ. Arsskr. (1958) 21–39
↑ Huxley J. 1959. Clades and grades. In Cain A.J. (ed) Function and taxonomic importance. Systematics Association, London.
↑ Mayr, Ernst 1982. The growth of biological thought. Harvard. p614
↑ Bather F.A. 1927. Biological classification: past and present. Proc. Geol. Soc. 83, 62–104

[1] Futuyma D.J. 1986. Evolutionary biology. 2nd ed, Sinauer. p288

[2] Futuyma D.J. 2005. Evolution. Sinauer. p84 and figure 4.17

[3] Huxley J.S. 1958. Evolutionary processes and taxonomy with special reference to grades. Uppsala Univ. Arsskr. (1958) 21–39

[4] Huxley J. 1959. Clades and grades. In Cain A.J. (ed) Function and taxonomic importance. Systematics Association, London.

[Ernst-5] Mayr, Ernst 1982. The growth of biological thought. Harvard. p614

[6] Bather F.A. 1927. Biological classification: past and present. Proc. Geol. Soc. 83, 62–104

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