"Love does transcend DNA...I have read about and seen instances of love even cutting across species. Cats have adopted abandoned puppies, and vice-versa. Even one instance of a bird adopting a cat has happened. Even the case of people having pets and treating them like their own children is rampant."

These are rare exceptions to the rule.

There are also many instances of lions killing young leopards, and vice versa.

In the wild, canines would likely kill young felines. And, if given a chance, depending on the species of feline(if they cat was big enough) vice versa

A young antelope was seperated from its herd. Because predators were not far behind, it sought sanctuary with a zebra herd. The zebras refused to allow the antelope to hang out among them.

Speaking of the true nature of dogs, their wild forms (wolves) live in packs that have an alpha male and an alpha female. The alpha couple are the only ones that breed. The alpha female will kill the puppies of other females, generally.

If a sheep or a calves approaches a female who is not his mother and tries to suckle, he or she will get butted by that angry female.

I'm not denying that exceptions exist, but in all species, preferences tend to be given towards relatives!