RE: The strange case for human beings having descended from ....?
hmmm good point, it's all about how you define it. But what you're really saying is that regardless of definitions the more different two critters are different the more rare it is to get any viable young from them, and yeah I think that is super true!!
One of the things about backcrossing that's kinda cool is that it can improve fertility. So if a random weird lifeform is able to live long enough to breed, it gets easier and easier down the line.
There's a couple of quotes that I really enjoy.
God didn't put pigs and humans in different taxonomic orders. Taxonomists did.
I have no idea where it comes from, but I do appreciate it...after all taxonomic orders are contrivances of humans, and even if we are bringing a substantial amount of insight, and pattern recognition to bear, I do think it is ever foolish to consider our own machinations as law.
Also, I really appreciate this by Rupert Sheldrake
Governments have laws. Nature has habits.
I wouldn't call explaining phenomena as "law", it's just our silly minds trying to make sense of reality in whatever possible way we can.
It definitely holds predictive capabilities, so I'll accept it. :^) However, there is a much better discipline that is now an addition to taxonomy; Cladistics. I don't know much about it on the same level I do taxonomy, but I know taxonomy now requires it to function much more properly in describing things.