Sir

Lewin in his engaging Concepts essay (Nature 410, 637; 2001) asserts that unless “demanded by expediency”, recent changes in taxonomy “muddle our language, and could introduce confusion in our libraries”. Two of his examples involve traditional groups that are unambiguously paraphyletic (each of them includes an ancestor but not all of its descendants), and they nicely illustrate why monophyletic taxa (those comprised of a common ancestor and all of its descendants) are preferable for teaching, research and influencing public attitudes towards nature.

Lewin claims that molecular phylogenetics has led to “a host of new problems”: for example, “Because crocodiles are believed to be more closely related to birds than they are to turtles ... are sparrows just feathered reptiles, and does ornithology become merely a branch of herpetology?”. That birds and crocodiles are each other's closest living relatives was a consensus view long before the advent of DNA sequencing, as has the conclusion that reptiles (including birds) are more closely related to mammals than they are to amphibians. Herpetology, defined monophyletically as the biology of tetrapods, thus does incorporate mammalogy and ornithology, but this no more makes sparrows “just” feathered reptiles than it reduces bats to “just” winged mammals; ornithology is no more “merely” a branch of herpetology than the latter is “merely” a part of vertebrate biology.

More important, traditional failure to taxonomically formalize a close relationship between crocodilians and birds obscures their similarities in parental care, acoustic communication and various internal traits. Perhaps that failure also explains why some recent analyses of life-history evolution in each group fail to cite work on the other, and why they also ignore a substantial literature on reproduction in closely related, extinct archosaurs.

Lewin correctly notes that the coelacanth Latimeria “is closer to humans than it is to herrings”, but then complains, “so what price ichthyology?”. Actually, the incredible panoply of fishes is done an injustice by traditional recognition of two basal taxa, one of them spectacularly successful (there are more than 20,000 species of ray-fins) and the other usually viewed as an evolutionary dead-end (Latimeria and lung-fishes).

A monophyletic perspective enriches ichthyology by, instead, emphasizing that the adaptive radiation of fishes includes two more-or-less equally speciose subclades, one largely confined to water (the ray-fins) and the other represented by both aquatic and terrestrial forms (coelacanths, lung-fishes, tetrapods).

Of course, one could argue that tetrapods are special because they move about on land and have changed a lot, but then so have walking catfish, swamp eels and mudskippers, all of which we appropriately leave in with other ray-finned fishes.

Lewin disapproves of new names and altered meanings for old names, whereas my experience is that students are inspired by the underlying rationale for such changes. Lay people likewise are intrigued by behavioural similarities between crocodilians and birds, and amused by the realization that we are all fishes. Rather than hindering biology, increasingly accurate and phylogenetically based taxonomy promotes the study and appreciation of life's diversity.