Such expressions as that famous one of Linnæus, and which we often meet with in a more or less concealed form, that the characters do not make the genus, but that the genus gives the characters, seem to imply that something more is included in our classification, than mere resemblance. I believe that something more is included; and that propinquity of descent,—the only known cause of the similarity of organic beings,—is the bond, hidden as it is by various degrees of modification, which is partially revealed to us by our classifications (Darwin, 1859, p. 413f).

Wednesday, 21 May 2008

Defining Phenetics ... one last time

The term phenetic is defined in the Oxford English Dictionary (OED) (online version) as:
"Designating or relating to the classification of organisms on the basis of their observed similarities and differences (often assessed in numerical terms), without reference to functional significance or evolutionary relationships".
The term was first used by Cain and Harrison (1960) "[f]ollowing a suggestion made by Mr. H. K. Pusey, we shall refer to the arrangement by overall similarity, based on all available characters without any weighting as phenetic, since it employs all observable characters (including of course genetic data when available)" (Cain and Harrison, 1960: 3).

The OED defines the term phenetics as "phenetic taxonomy or the systematics of phenotypes". It was first used by Ehrlich & Holm (1963) to refer to "[t]he study of relationships of individuals [which] may permit the creation of a 'population phenetics' which will add new dimensions to the study of microevolution" (Ehrlich & Holm, 1963: 240-2).

If the first definition of phenetic is true, then phenetics by definition cannot find evolutionary or phylogenetic relationships, only similarities.

References
Cain A.J. & Harrison G.A. (1960) Phyletic Weighting. Proceedings of the Zoological Society of London 135: 1–31.
Ehrlich P. & Holm R.W. (1963) Letter to the Editor. Science 139: 240 – 242.
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