Um NO !!
If B1 is the current form and then off shoots a B2, B2 IS not BOUND by any laws to destroy B1 and most likwly will merge with B1 to produce more B2's and even B3's later .
Come on JP ( self digs ya ! but dont get pig headed in defending your point ) ..
Vero 99 has given a good example of a possible situation ..
Or heres evolution for you that can be tracked !! reveiw the history of WINDOWS 3.1 to XP Pro ..shure its not animals but same concept .. Then look to just about anything still on the planet we just might not be able to track the changes at this time nature is slower than us mini Gods in changeing things ..

But once again slef agrees with the core of your thinking evolution alone will not explain the vast amouts of forms the DNA seems to have created ,hell it dont even explain plants square cells vs animals round cells and howcome there are no plantimals ?? harnesting the BEST of both traits ??or even crystal creatures ? Self knows there is a Mind behind the madness lol !!