Expert: Dana Krempels, Ph.D. - 5/25/2007

Question
Is there any biological reason for laughter?  Why are only humans capable of it, and what is the evolutionary purpose?  What causes a baby to laugh, as opposed to an adolescent or adult?

Answer
Dear Brian,

What's the deal with laughter?  Why do we do it?

This is a question still being pondered by both biologists and pschologists, and no definitive answer exists.  There *are* biological benefits to laughter--that much we know.  It increases blood flow, increases the secretion of hormones that reduce stress, and can help cement social bonds between humans.

And don't think that only humans laugh.  Other species have their own versions of laughter, as anyone who has played with a happy dog can tell you (they have a form of rapid panting with the eyes "crinkled up" as laughter).  Rats and other rodents laugh; rabbits and hares laugh with their whole bodies (I've seen them do it!), and I would suspect that most mammals have some form of behavior that's equivalent (and perhaps even homologous to) laughter.  

If any evolutionary purpose can be ascribed to laughter, my guess would be that those human ancestors who engaged in it were perhaps better at social bonding than their non-laughing conspecifics (apes also laugh (though not with a vocalized "ha ha ha"; it's more of a voiceless "panting" laugh), so it's likely that the common ancestor of human and chimp also had something like laughing.  We are social primates, and it's possible that ancestral animals who laughed (rodents and primates) may have been more successful at forming social bonds, securing mates and successfully producing offspring.  That's what natural selection is all about.  But again, that's just an educated guess.  No one really knows for sure.

No one can get inside a baby's head to know what elicits laughter, but it's probably more reflexive than mental.  Even adolescents and adults don't *consciously* laugh; they just laugh when a particular stimulus makes them do so.  The stimuli may differ from culture to culture (what's funny is somewhat different if you're in Canada vs. China), but the laugh itself is universally understood social signal.

There's an interesting article here about the function and evolutionary roots of laughter:

http://www.msnbc.msn.com/id/3077386/

I think you'll enjoy it!

Take care and keep laughing,

Dana