December 4, 2003
No one definition has satisfied all naturalists, yet every naturalist knows vaguely what he means when he speaks of a species.
Charles Darwin, 1859
A family of chipmunks has taken up residence by my house and they have been eating my birdseed. I am trying to make friends with them. They are delightful animals. I mentioned this to Barbara Wilson, who is our local authority on wild rodents. She asked me what species they were. I had no idea, so I looked it up in my Field Guide to the Mammals of America and Northern Mexico. Apparently there are two species that are found in this area. The distinguishing feature that would enable me to tell one species from another has to do with the color pattern of the back of the ears. I tried looking at the back of their ears and didn't see much. I gave up; a chipmunk is a chipmunk.
We hear a lot about "endangered species." Everyone knows what the word "endangered" means, but what about "species?" The word species has been around for a long time, probably long before Linnaeus(1707-1778) classified various life forms according to the things that they had in common and the ways in which they differed. Darwin's book The Origin of Species caused a minor revolution in the middle eighteen hundreds. Darwin knew almost nothing about what is now called genetics. No one did. The subject really didn't exist before 1900, when Gregor Mendel's work was re-discovered.
Well, what is a species? Zoologist and botanists have as many definitions of the word as there are for the word "love." The most precise, and genetically accurate, definition is that two similar life forms are members of different species if they cannot interbreed and produce fertile offspring. The horse(Equus caballus) and donkey(Equus asinus asinus) can breed and produce a mule, which is usually sterile. Consequently, they are considered to be different species. However, the percheron horse and the pony are considered to be members of the same species. A mastif and a chihuahua are also considered as members of the same species even though I can't see how they could get it on in order to produce offspring. If someone from another planet came here and saw those two dogs, he would surely classify them as different species, if not as different genera. This was a central argument for evolution in Charles Darwin's Origin of Species.
The dog(Canis familiaris) and the wolf(Canis lupus) are considered separate species even though they can interbreed and produce fertile offspring. The dog was probably derived from the domestication of the European wolf. Of course, all animals are related if you go back far enough.
The Ivory Billed Woodpecker of the southern US is listed as possibly extinct. When I look at pictures of one it looks a lot like the Pileated Woodpecker which is found in my area and is not only not extinct, but not even considered endangered.
Taxonomists are people who specialize in classifying organisms. They are to biology what lexicographers are to language. There is an old wise crack : "Yesterday I couldn't even spell lexicographer, and now I are one."