It’s a pretty safe bet that anyone who talks about “natural law” has never really studied biology. For centuries, theologians have written about what is “natural” and “unnatural” in terms of sexual behavior. That approach requires a selectivity beyond the reach of most honest people.
What follows is the type of observation that never made it into the discussion. It is the observation of one of Captain Scott’s explorers observations about the “depravity” they observed among the penguins. At the time the notes were censored, but they were recently rediscovered at the Natural History Museum one hundred years after they were written.