It's the easiest test of attraction.
Ask anyone what he or she most values in a date or a marriage partner, and sense of humor is likely to come to the top of the list. But when Norm Li and I asked several hundred students in my classes what they meant by a good sense of humor in a date, men and women gave slightly different answers.
The women were more likely to say a man has a good sense of humor when "he makes me laugh;" the men were more likely to mean "someone who laughs at my jokes."
We believe there's a reason for the sex difference, linked to what evolutionary biologists call "sexual selection." Throughout the animal kingdom, males are more likely to show off (think: peacocks), whereas females are more likely to play careful comparison shoppers, evaluating the male's displays.
Why? Biologists have shown it's because females have to invest a lot in any given offspring, while the males can often get by with a minimal investment of sperm.
To attract the more selective females, the males need to compete, hoping to demonstrate that they have better characteristics to pass on to the offspring. The story is a little more complex in humans, where men typically stay around and help the offspring, but the biological price is still usually a lot higher for a human female (who must carry the fetus and nurse the newborn, besides providing more of the childcare).
Nevertheless, men in a mating frame of mind do show off a lot more than females, becoming more creative, spending more frivolously, or doing crazy stunts on their skateboards. In fact, men will go to ridiculous lengths men in the interest of attracting women.
Norm and I never published those findings, because other researchers had a similar hunch, and published their findings before we did.
Meanwhile, Norm and several other colleagues branched off to study the broader communication function of humor. Does your spouse still care for you? Are you getting along with your boss? Is that blind date bored or excited with you?
A great gauge of their feelings is whether they're laughing at your jokes. You don't need to be a stage comic, either.
If someone really likes you, you can tell them a joke about a chicken crossing the road and they're likely to laugh. If they don't like you, you can use Woody Allen's best material and you'll hear, "I don't get it. Are you trying to be funny?"