The researchers thought the motivated females would keep their hands in the water longer than they would without the monetary motivation, thus narrowing the gap between Tarzan and Jane because now the females were motivated to stand the pain.
But "we got the complete reversal of what we expected," Fillingim says.
There wasn't any difference for the females. But the men who were offered up to $20 lasted longer than the men who were offered just one lousy buck.
Fillingim says the study suggests that there is much more at work here than the motivation to deny pain.
"The gender-sexual-male macho thing is clearly not the only explanation for sex differences in pain," he says, because even motivated women are not better equipped to deal with pain. "If gender is playing a major role it may not be based on motivation (like the need to protect the male image.) There may be another path."
But, as he admits, maybe he chose the wrong motivation.
"It might be that some other incentive would work better for women," he says.
And of course, no one's saying cheap, cheap, cheap here, but 20 bucks can't buy a heap of motivation these days.
Women’s Pain Varies by Cycle
But at least the project suggests that the motivation to protect the male image is not the only thing at work. That dovetails with other research projects, notably at the University of Michigan, that reveal fundamental biochemical differences in how men and women deal with pain. They found that sex hormones like estrogen play a big part in how we react to pain.
That finding helps explain how women, the so-called weaker sex, can deal with the excruciating pain of childbirth. New non-invasive brain-imaging techniques have allowed these researchers peer inside the brain, examining the chemical processes that occur in the presence of pain.
Estrogen levels among women vary widely during the monthly menstrual cycle, and during pregnancy, and the research shows that estrogen plays a critical role in helping the brain's natural ability to suppress pain.
"When estrogen levels are high, the brain's natural painkiller system responds more potently when a painful experience occurs, releasing chemicals called endorphins or enkephalins that dampen the pain signals received by the brain," the Michigan team reported. "But when estrogen is low, the same system doesn't typically control pain nearly as effectively."
So a woman's ability to withstand pain changes repeatedly over time.
And researchers at the University of California, San Francisco, have found that while women may be less tolerant to the sudden onslaught of acute pain, there is no difference between men and women when it comes to dealing with chronic pain, like cancer. Men and women were found to suffer equally with cancer of the bone.
So, many questions remain. But the "me Tarzan" bit is a little weaker today than it was just a few years ago. We appear to be far more complicated than that, both male and female.
Lee Dye’s column appears weekly on ABCNEWS.com. A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.