Phenetics

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This article is about the classification of organisms. For the study of speech sounds, see Phonetics.

In

phylogeny or evolutionary relation. It is related closely to numerical taxonomy which is concerned with the use of numerical methods for taxonomic classification. Many people contributed to the development of phenetics, but the most influential were Peter Sneath and Robert R. Sokal. Their books are still primary references for this sub-discipline, although now out of print.[1]

Phenetics has been largely superseded by

neighbor-joining, are used for phylogenetics, as a reasonable approximation of phylogeny when more advanced methods (such as Bayesian inference
) are too expensive computationally.

Phenetic techniques include various forms of clustering and ordination. These are sophisticated methods of reducing the variation displayed by organisms to a manageable degree. In practice this means measuring dozens of variables, and then presenting them as two- or three-dimensional graphs. Much of the technical challenge of phenetics concerns balancing the loss of information due to such a reduction against the ease of interpreting the resulting graphs.

The method can be traced back to 1763 and Michel Adanson (in his Familles des plantes) because of two shared basic principles – overall similarity and equal weighting – and modern pheneticists are sometimes termed neo-Adansonians.[2]

Difference from cladistics

Phenetic analyses are "

monophyletic. Phenetic analyses are also liable to be rendered inaccurate by convergent evolution and adaptive radiation
. Cladistic methods attempt to solve those problems.

Consider for example

monophyletic
too, but their shared traits were present in the ancestors of all songbirds already. It is the loss of these ancestral traits rather than their presence that signifies which songbirds are more closely related to each other than to other songbirds. However, the requirement that taxa be monophyletic – rather than paraphyletic as for the case of the Corvida – is itself part of the cladistic method of taxonomy, not necessarily obeyed absolutely by other methods.

The two methods are not mutually exclusive. There is no reason why, e.g., species identified using phenetics cannot subsequently be subjected to cladistic analysis, to determine their evolutionary relationships. Phenetic methods can also be superior to cladistics when only the distinctness of related taxa is important, as the computational requirements are less.[3]

The history of pheneticism and cladism as rival taxonomic systems is analysed in David Hull's 1988 book Science as a Process.[4]

Current usage

Traditionally there was much debate between pheneticists and cladists, as both methods were proposed initially to resolve evolutionary relationships. One of the most noteworthy applications of phenetics were the

Ciconiiformes" or the "Corvida") have been rejected. However, with computers growing increasingly powerful and widespread, more refined cladistic algorithms became available which could test the suggestions of Willi Hennig
. The results of cladistic analyses were proven superior to those of phenetic methods, at least for resolving phylogenies.

Many systematists continue to use phenetic methods, particularly to address species-level questions. While a major goal of taxonomy remains describing the 'tree of life' – the evolutionary relationships of all species – for

fieldwork one needs to be able to separate one taxon
from another. Classifying diverse groups of closely related organisms that differ very subtly is difficult using a cladistic method. Phenetics provides numerical methods for examining patterns of variation, allowing researchers to identify discrete groups that can be classified as species.

Modern applications of phenetics are common for

DNA sequences
.

In addition, many of the techniques developed by phenetic taxonomists have been adopted and extended by

community ecologists, due to a similar need to deal with large amounts of data.[5]

See also

References

  1. ^ Sneath, P. H. A. & R. R. Sokal. 1973. Numerical taxonomy – The principles and practice of numerical classification. W. H. Freeman, San Francisco. xv + 573 p.
  2. ^ Schuh, Randall. 2000. Biological Systematics, p. 6. Cornell U. Press.
  3. ^ Lindberg, David R. "Principals of Phylogenetic Systematics: Phenetics" (PDF). Integrative Biology 200A Principles of Phylogenetics: Systematics. University of Berkeley. Retrieved 10 October 2018.
  4. ^ Hull, David L. (1988). Science as a process: an evolutionary account of the social and conceptual development of science. Chicago, Illinois: University of Chicago Press.
  5. ^ Legendre, Pierre & Louis Legendre. 1998. Numerical ecology. 2nd English edition. Elsevier Science BV, Amsterdam. xv + 853 pages.
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