Partner Series

It's obvious that animals hook up, at least during mating season, but do they like it? According to experts, there are two answers: "yes" and "it is impossible to know."

"Mosquitoes, I don't know," said Mark Bekoff, a University of Colorado biologist and author of "The Emotional Lives of Animals" (New World Library, 2007), "but across mammals, they enjoy sex."

In fact the enjoyment of sex among humans and among animals may be similar in that it's experienced in primitive parts of the brain.

Not only do animals enjoy the deed, they also likely have orgasms, Bekoff said. They are difficult to measure directly but by watching facial expressions, body movements and muscle relaxation, many scientists have concluded that animals reach a pleasurable climax, he said.

Then why do some animals abstain most of the year?

"It is not that they don't like it, it is just who they are," Bekoff said. In the wild, having sex makes one vulnerable to attack. For example, a male wolf gets "locked" inside the female for up to a half hour, he said. Besides, if wolves got it on during the summer, it would be poor family planning; their delicate pups would be born in the dead of winter, he said.

Humans, though, are not the only species that wants sex regardless of reproductive timing. Bonobos and possibly dolphins also pursue sex recreationally, Bekoff said.

Still, we can never completely know another being's emotional state, Bekoff points out, adding that it can even be hard to judge that of a human. And we can't ask a tomcat how his date went last night.

Sweets and sex as well as drugs, winning the lotto and every other rewarding experience stimulate the same brain circuit, said Kent Berridge, a biopsychologist at the University of Michigan, and this pleasure circuit is common to both human and non-human animals. His experiments suggest a further homology, one of emotional experience.

"Our chief anatomical difference from [other animals] is up in the prefrontal cortex," explained Berridge, but the generation of pleasure is happening at "lower" brain structures. The human cortex may interpret pleasurable sensations and assign them special meaning (or not). In this way, a human's experience of sex may be qualitatively different than an animal's, but no less (or more) enjoyable.

And of course, Nature offers her own proof that sex is pleasurable: plentiful offspring.

"There are damn good evolutionary reasons for animals to enjoy sex and have orgasms," said Bekoff. "My null hypothesis is that they do," he said, adding a challenge: "Prove that they don't."