[jujumantb]

Originally Posted by c312

But there's a difference in believing that natural selection led to adaptive changes within a species and believing that natural selection led to changes from a species to a new species.

well, to a biologist that wouldnt make sense.

lets first define what a species is, which a commonly accepted definition is "a reproductively isolated population". now, with this definition, all it takes for a new species to arise is to have those "adaptive changes" you state change their reproductive status within a population. Generally, this occurs through whats called speciation where a single reproductively isolated population is divided for a number of reasons into two or more populations.

Over many generations, these two populations will go through natural selection in their environments (your "adaptive changes") and eventually lose the ability or drive to breed with eachother. Thus, even if those populations were reintroduced with eachother, they would not breed, and, according to the defition of a species, we end up with one or more new species.

As this happens over billions of years, we get that branching effect with more and more variance and more and more species. We see how the only process identified here in the creation of new species is, in fact, natural selection (genetic drift too, but thats not important in this discussion)

So if you believe in natural selection, you really cannot present a good arguement about how you dont believe it can create new species.