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Switching to phylogenetics

The system of phylogenetic classification works differently than the traditional system.

  1. Looking at rank
    Phylogenetic classification has two main advantages over the Linnaean system. First, phylogenetic classification tells you something important about the organism: its evolutionary history. Second, phylogenetic classification does not attempt to "rank" organisms. On the other hand, the Linnaean classification "ranks" groups of organisms artificially into kingdoms, phyla, orders, etc. This can be misleading as it seems to suggest, for example, that a cat family is somehow comparable to an orchid family. However, they are not comparable:
    • One may have a longer history than the other. The first representatives of the cat family Felidae probably lived about 30 million years ago, while the first orchids may have lived more than 100 million years ago.

    • They may have a different level of diversity. There are about 35 cat species and 20,000 orchid species.

    • They may have different degrees of biological differentiation. Many orchids belonging to different genera are able to hybridize. But the same is not true of cats — house cats (belonging to the genus Felis) and lions (belonging to the genus Panthera) cannot form hybrids.
Orchids of these two different genera hybridize... ...but cats of these two different genera do not.
Laelia purpurata crosses with Cattleya mossiae House cat Lion
Laelia   Cattleya Felis   Panthera

There is just no reason to think that any two identically ranked groups are comparable and by suggesting that they are, the Linnaean system is misleading.

Orchid images © Greg Allikas; House cat image courtesy of Judy Scotchmoor, UCMP; Lion image courtesy of Gerald and Buff Corsi © California Academy of Sciences.

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Teach your students about phylogenetic classification with Classification and evolution, a classroom activity for grades 9-12.

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