Wait a minute here.....
Lion & Tiger... hmmmm "cat family"... that is realistic that they could breed...
Same thing with Mule and Hinny... "horse family"
Just because a line "ends," becomes 'sterile', 'drifts apart' does not automatically say "hey, they all came from one thing"
In fact, to me, it means "less variety", they can only breed with those of their "family."
No one has ever explained how a bear, raccoon, cat, whatever, can become a porcupine? hmm.... quillls, throwing them, etc. Ok, one piece of fur becomes a quill... Then, a million years later, another pice of fur becomes a quilll... then that family of "quill creatures" dies off... Start over... How many quills does a porcupine have? 30,000.
Not that I believe in a "God" anymore, however, I do see evidence of design.... So, let's say I believe in "an inventor." Not that I have all the answers, nope... but I won't accept theories or guesses or assumptions or leaps in logic any, any, more. Science will be put to the test, taken to task, just like the WT.