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Name: Sandra F.
Status: Educator
Age: 40s
Location: N/A
Country: N/A
Date: October 2002

Hello. I thought that the definition of species was a population that can interbreed. Why, then, are dogs (Canis familiaris), wolves (Canis lupus & rufus), and coyotes (Canis latrans) considered separate species if they can interbreed? The offspring are not infertile, as in the case of the mule. Thank you.

The inexactitudes of taxonomy and science.

Peter Faletra Ph.D.
Assistant Director
Science Education
Office of Science
Department of Energy

There is always an exception to every rule isn't there? Dogs and wolves are so close to each other in evolutionary time, i.e., their common ancestor was very recent, that apparently they can interbreed and have fertile offspring. Much of this has to do with the chromosome number and being able to match each chromosome during meiosis. Horses and donkeys can produce mules because there isn't a problem at fertilization but the mule offspring are left with an odd number of chromosomes. So when and if two mules tried to mate, at fertilization, there would be a problem matching genetic information. The offspring would fail to develop.


Your query is important. However, one must realize that the definition of "species" is man-made, much like the dog! The definition is full of holes and certainly seems inconsistent. You only mention one of many other striking examples, but there is a catch to the definition..... One rule of thumb that is generally recognized relates to the domesticated animals, in that, they don't count! Man has messed up natural selection with artifical selection and the dog would not be found in North America if it were not for their human connection. It has been found that several other species have been breed with distant relatives that would not normally be found in the same location. Thanks to man again! You migfht recall the attempt to develop a cat-dog called a Cog several years ago. Ok, the definition of species usually includes a statement that refers to "naturally occurring" and is meant to exclude human interference so that is how your question has to be answered. I hope this all helps some.

Steve Sample

I am not a geneticist or taxonomist, so you may get a very different answer from those perspectives, but from this naturalist's view, species are really constructions of the human mind, just like language and other systems of thought, that allow us to talk about and make some kind of sense of the world. Through the process of adaptation and evolution relationships between organisms are constantly in flux, so that some "species" are in the process of splitting, while some populations that had become separated may be back in situations where they can interbreed. "Species" cannot come into being instantly, so there is always a process - evolution - going on. In other words, nature is not nearly so neat as we sometimes make it out to be.

J. Elliott

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