From Cosmiclog at MSNBC...
How do you graph the evolution of a laugh? Researchers tickled babies and six different kinds of apes, quantified their giggles, and found that the patterns fit a classic evolutionary tree.
Those patterns hint at the ancient origins of human hilarity and suggest that other social species - including apes, dogs and rats - really, truly laugh as well.
"What we can say is that laughter goes back at least 10 to 16 million years," said University of Portsmouth primatologist Marina Davila Ross, one of the researchers behind the study published online today in the journal Current Biology. "It could go farther than that."
A prominent researcher in the specialized field of animal laughter, Jaak Panksepp of Washington State University, said it definitely goes farther back than that. "I personally think that a credible laughter concept can, and already has been, extended to mammalian species as lowly as the rat..."