Re:how, exactly (Score 1)

Maybe development of new species is not something that happens within a generation.

You could have some off-springs that mutate somewhat, who then pro-create with others also carrying a mutation, eventually creating a mutation that's incompatible with another branch spawned from their common ancestors. Most of the branches die off and/or recombine and only couple truly distinctive ones survive.

Those surviving branches become incompatible for breeding purposes and there's your new species.

P.