Sometimes some silly atheists go blathering on in a silly Rousseauean vein about "Nature"'s "purity," and how an example of this is that humans are the only species so "depraved" (Can you tell that I really, really hate Rousseau? You can? Good!) as to have something like religion.
Ridiculous. How on Earth do we supposedly know that no other species have religious beliefs? We know nothing of the sort. The absurd assumption that other species lack emotions similar to ours seems finally to be losing currency among zoologists. Let's toss out this assumption about their lacking religious beliefs, too, until we have some reason to assume such a thing.
Don't forget: evolution continues. Even if humans once were the only species with religious beliefs -- that's a tremendously huge "if," but let's assume it for a moment just for the sake of argument -- for tens of thousands of years, humans have both been religious and had close contact with domesticated animal species. Tens of thousands of years in which they've been watching us closely.
I repeat: the assumption that other species have no religious beliefs is absurd, premature, unfounded.
If you're agreeing with me, and about to shout: "Yes! And Exhibit A are the so-called 'elephants' graveyards'!", No. What you may have heard about elephants' graveyards is mostly myth. The most likely explanation for these collections of elephants' skeletons is that they were dumped there by poachers after they killed the elephants and took their tusks.
I have no Exhibit A which is going to make people exclaim and slap their foreheads and insist that animals are religious. I, in fact, am not insisting that animals are religious. I am merely asserting that we have no reason to rule it out, and pointing out how many times already we have realized that certain assumptions about our non-relatedness to other species were incorrect.