Having a pet or adopting a pet, biologists say, is a uniquely human activity. If this is true, what's going on here with this long-tailed macaque that was seen cuddling a kitten in Monkey Forest Park, on the island of Bali, Indonesia? The photographer observed the monkey treating the kitten as a pet, cuddling it, nuzzling it and even grooming it. No one seems to know how the kitten and monkey got together but the kitten seemed perfectly happy.

And what about the colony of bearded capuchin monkeys found to be caring for a baby marmoset, another species of monkey? The monkeys treated Fortunata (the name the researches gave the marmoset) like any human couple might treat their pet cat or dog, They played with her, cradled her and carried her around.

Both of these situations raise the questions: are humans really the only ones who have pets? And why don't animals keep pets? Psychologist and author Hal Herzog took it upon himself to answer these questions and in his research he found plenty of examples of long-term attachments between animals of different species but only when they were captive or semi-captive in zoos, wildlife sanctuaries or research labs.

To be truly reflective of the species and conclusive, he felt the activity must occur in the wild. He took to scouring academic journals, consulting a host of animal behavorists and reached the conclusion that pet keeping just didn't happen in the wild. Humans were thus the only animals who truly kept pets.

That's about when the story of Fortunata reached his ears and doubt flickered across his theory. However, Dr. Herzog soon learned that while the capuchins were not confined, the situation was not completely wild either. The monkeys were given food every day as part of a program designed to promote ecotourism. Also, it was unclear to him whether Fortunata was a case of pet or adoption.

In the end, he concluded that in order to qualify as a pet-keeping, the relationship must be relatively long-lasting and not have obvious benefits to the pet's "owner". Since the capuchins had lived with Fortunata for 14 months, he believes they simply are an exception that proves the more general rule that non-human animals don't keep pets. As for the macaque and kitten in Bali, since they have just recently been discovered, only time will tell what they truly are to each other.