... evidence of evolution of different species that then later merged to become one new species.
One of the advantages the frogs would have is that the first batch would have numerous offspring to then mate with.
They would have to be closely related species, or actually sub-species, (by definition of species) to mate.
I think of horse and donkey and similar occurring -- such offspring would need to mate with either parent type.
There certainly is not a loss of genetic material in this situation ...
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