There are a whole lot things that human beings do that you would not like---but they do them despite your disapproval. What "animal" has been performing clitorectomy routinely on its female offspring for a thousand years? It's not aadvarks. What animal instituted the practice of no sex before marriage only a few hundred years ago? Before that, following the betrothal system, pregnancy came before marriage.
Normal human beings are weirder than you would like to consider.
Really? I hadn't noticed! Shucks...I must be one of those poor naive religious folks.
You seem to be adopting the idea--and correct me if I'm wrong--that "normal" is defined by what actually occurs in human populations. So if people do it...then it must be normal.
But is that really accurate? So if, say, a culture evolves that promotes statutory rape...then that behavior is normal?
There isn't a society alive that works that way though...every society has a system of "ought". Though of course there are people that go against that system, the system doesn't go away because of those who buck it. And I've never heard of any culture, frankly, that basis said system on what it views in the animal kingdom.