|MadSci Network: Evolution|
Let's see now, just answering off the top of my head (no references except my Webster's New World) In biological classification, a species is a division of a genus. A working definition of a species is a group of plants or animals that have a high degree of similarity and generally interbreed with themselves. Take dogs (canis familiaris) or cats (felis catus). Dogs are thought of as being their own species. They can interbreed with wolves, but that doesn't happen usually in nature. So the interbreeding thing isn't absolute. And just a few mutations will not a species make. But when the chromosomes are of different number or are different enough, when the egg meets the sperm, the inability of the chromosomes to pair can prevent a viable offspring from forming. Or, the offspring is viable but sterile, for example horses and donkeys make mules, which are sterile. Lions and tigers make ligers and tiglions, depending on which is the father, and I think one of those combinations is fertile and the other is sterile. Have we ever seen a new species arise? Well, the development of the mamalian species occurred over tens of millions of years. There was plenty of time for geographic isolation to result in divergence through selection of variants, reproductive isolation and then speciation. The divergence of birds on the Galapagos clued Darwin in to the idea that natural selection generates new species. Actually this evolution happened rather "quickly". The Galapagos are quite "young" volcanic islands being only several million years old. But that's still millions! But wait a minute. Dogs developed from wolves coexisting with man and then being domesticated. This happened in the last ten thousand years or so. So there's a new species that people have actually witnessed the creation of. And cats are a new species that was developed by man in Egypt also about ten thousand years ago from some wild ancestor. People did that too. So I guess you can say we've seen the development of these new species within human time. I think there are about a million and a half different species named and most of those are insects and most of the insects are beetles. I've heard that beetles get so specialized that even different individual trees in the tropics can have their own species of beetles. That's pretty extreme if you ask me, but that being the case, there should be many recent beetle species.
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