The biological species concept says that a species is a population (or group of populations) that have the potential to interbreed and produce viable, fertile offspring. (Campbell's
Biology 5th ed.)
The biological species concept is not applicable in all situations, such as when dealing with asexual organisms. Some different species can mate and create fertile and non-fertile hybrids. Mules are non-fertile. Many fish species can hybridize within the same genus. Wolf and dog and coyote orgies, oh my! The biological species concept seems to break down in many situations, doesn't it?
However, one thing that no one that I know of mentioned was that reproductive isolation isn't just at the genetic level. It also involves habitat isolation, temporal isolation, behavioral isolation, mechanical isolation and gametic isolation. (Campbell)
Some organisms don't normally meet (lions and tigers) in the wild.
Species can also be isolated based on when they mate.
Some species are also just not attracted to other species, or they see the other species as food or competition.
Sometimes the parts just don't fit!
Sometimes the gametes, even if they are in the same general area (water, uterus), just aren't attracted (chemically) to each other.
The species that we see producing viable hybrids have either had their normal environmental barriers broken down or are just not that far away from their common ancestry with another species.
The "discrepencies" in the biological species concept, however, do not strengthen the case against speciation nor show that "kinds" actually might mean something.
quote:
I don't like the methods we use to break down species. Why we could use the same methods on man, well we do in a sense with the term race, but whats keeping science from breaking man down like they have the finch?
The barriers between the finches, I would say, would most likely be behavioral. Each finch has a specialized beak for its specific food. Also, habitat isolation would also probably play a part.
The bahavioral and habitat barriers that exist for the finches do not exist for humans.