[ml/nj]

If I continue the experiment long enough, and keep selecting for new attributes, eventually they will be so different that they will no longer be able to interbreed at all. At some point they are no longer guppies, but become some new species.

Really?

You may believe this, but there is no evidence that I know of to support such a statement. Do you think the ones that are not guppies any longer will have a different chromosome count?

ML/NJ

[MikeJ]

If I continue the experiment long enough, and keep selecting for new attributes, eventually they will be so different that they will no longer be able to interbreed at all. At some point they are no longer guppies, but become some new species.

Really?

You may believe this, but there is no evidence that I know of to support such a statement. Do you think the ones that are not guppies any longer will have a different chromosome count?

Well, according to Darwin, this where different species come from. You may or may not choose believe this explanation, but any book which explains the idea of Natural Selection can describe it for you in detail.

There are numerous examples of selective breeding being used to create new species, just as I described. As I understand it, modern corn is now so different from the original plant from which it was derived (maize) that they can no longer pollinate one another. Maize and modern corn are now different species of plants.

WRT the chromosome count, the short answer is that these two groups of fish really will be genetically different. They may or may not have the same number of chromosomes, but it is the composition of the chromosomes, not their number, that really matters. (I'm guessing, but I'm pretty sure that apes and humans have the same number of chromosomes, yet they are clearly a different species).