While conniving is complex, love is simple. Because reproduction is a fundamental drive, common sense tells us that nature would make producing offspring a positive experience. That's the perspective of biological anthropologist Helen Fisher, PhD, who notes that chemicals in the brain produce the feelings associated with love (and lust, and long-term attachment) not just in humans but in a broad range of species. Obsessed with the object of your affection? That's probably because an elevated level of dopamine has driven down your serotonin levels, which in turn permits obsessive thinking. Similar chemistry is at work in elephants, lions, beavers, and a host of other creatures. To be sure, humans are the most eloquent animals when it comes to reflecting on feelings of love, but the neurobiology of the feelings themselves is widely shared.

Intelligence may be widely shared as well—and of all the things I've learned about animals over the years, this has been perhaps the biggest surprise. I'm not alone in that broadening of perspective. "I was something of a snob about where to look for animal intelligence," admits Karen Pryor, a behavioral biologist, "but over the years I've seen animals do things they're not 'supposed to' be able to do." Forty years ago, Pryor caused a stir when she demonstrated that a dolphin could invent its own tricks. Now she's gotten dogs to do the same.

The late zoologist Donald Griffin, a pioneer in the study of animal intelligence, would not be surprised. He always believed that some degree of awareness was present in many animals. For the sake of argument, let's say Griffin was right. If consciousness is broadly spread throughout the animal kingdom—if animals share to some degree the abilities and feelings that combine to make us human—what does that mean?

It shouldn't make a difference in how we treat animals—no creature need pass an awareness test to justify its existence—but, of course, it does. Once you've heard enough stories about the intelligence and valor of pigs (like Priscilla, who towed a struggling boy safely to shore in a Texas lake; or Harley de Swine, a Vietnamese pot-bellied pig who literally ran to work, such was his enthusiasm for helping head-injury patients at a medical facility in California), it's hard to keep eating pork. I should know: I gave it up, even though it was my favorite meat. The short, miserable life on a typical hog farm is bad enough, but the possibility that pigs might be aware of their situation is intolerable.

We tend to treat animals as commodities (useful for food, clothing, labor, research and experimentation, etc.) or as personalities (remember Free Willy?). Yet the evidence of animal awareness suggests a third choice: that animals are fellow participants in an unfolding evolutionary drama. We humans want to believe that we are special. The idea that we're intrinsically different from other animals gives us, among other things, the moral justification for treating those animals as so much stuff. But nature has no stake in any particular species, including humans. And if natural selection can produce identical shapes in animals with utterly different ancestries (witness the pangolin and anteater), perhaps it has also produced similar emotional states and mental tools in humans and, say, crows.

This perspective allows us to appreciate that other creatures besides ourselves might have a sense of humor, pride, even honor. And, we can hope, appreciation might lead to recognition of our deep bonds. We can see ourselves as the lone species capable of thought in a landscape otherwise populated with wind-up toys. Or we can embrace the idea of a world filled with many sentient beings, some of whom can scheme and joke, and some who would cooperate with humans to save their babies. Acknowledging consciousness in other species might be inconvenient for us comfort-seeking omnivores (it requires treating animals with respect—particularly the ones we eat), but I know which world I would rather inhabit.

Animals are especially captivating on camera. Watch video clips that stirred our souls and split our sides Watch

From the June 2009 issue of O, The Oprah Magazine.