Board Thread:Lore Discussion/@comment-9062114-20140323022721/@comment-202.156.8.10-20140323091139

As long as two types of organisms can breed together and produce fertile offspring, they are generally considered as one species, if their DNA is congruent enough. This is one underpinning of biology in general. If two seperate species breed to create a fertile hybrid, then we could have speciation. If a species diverges, then we got speciation too

One way to look at it: Man and Mer are one species, Khajits are GM mer (Azura did some magic meddling I think and so become a new species through divergent evolution, Argonians have and will always be seperate, being reptiles.

Or else: Man and Mer are two closely related species, so they bred to create Bretons as a third species (best example of hybrid vigor, seeing how OP bretons are), Khajits and Argonians are third species.

Parsimony makes the first more likely, I'd say Man, Mer and Khajit diverged from a common ancestor through magic meddling and evolution, while Argonians evolved all their characteristics and genius through convergent evolution and some magic.

--Some random science geek--