People joke about the differences between men and women: Men don't listen. Women can't read maps. Men snore more. Women are less likely to have affairs.
But are men and women really different or are those statements myths?
It turns out that science says men and women are different.
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At the University of Rochester, students were blindfolded and then led through a maze of tunnels that run underneath the campus.
The experimenter stayed behind them and guided them with a tap on the shoulder so they wouldn't run into anyone.
When the women were asked where a college building was, they rarely knew.
Men, however, have a better sense of spatial relations, according to the experiment. Most knew roughly where they were.
In contrast, at York University in Toronto, students were asked to wait in a cluttered room. After two minutes, the experimenter moved them to another room and asked the students to tell him every object in the room that they could remember.
Women typically gave incredibly detailed answers.
The men were more likely to say, "I dunno. There was some stuff there."
Many women went on and on.
Why are there differences like that or more men at the top levels of science?
Is it, as transgendered Stanford University neurobiologist Ben Barres says, all because of sexism? Or is it inborn, caused by the bath of testosterone boys get in the womb?
June Reinisch, a former Kinsey Institute director, studied data on thousands of baby girls and boys, and she concluded there were just inborn differences.
"Girls sat up without support earlier than boys did. Boys crawled independently, away from their caretaker, earlier than girls," Reinisch said.
Still, one could argue that even those differences happen because of some early sexist parenting.
But how do you explain behavior differences in newborns?
"So when they look at babies in the first 72 hours of life, they find that males and females are not identical in the way they behave," Reinisch said. "Males startle more than females. If you give a little puff of air on their abdomen, they startle much bigger and much more likely to startle than females, and females rhythmically mouth. They suck on their tongues. They move their lips and so forth more than males do."
Could this explain the myth that men don't listen?
"The male brain … actually has a harder time processing the female voice versus the male voice, which is a possible explanation to why we don't listen when our wives call us," Dr. Billy Goldberg said on "20/20."
Goldberg and Mark Leyner are co-authors of "Why Do Men Fall Asleep After Sex?"
They said it was true that men listened less because of biology.
"Male babies make less eye contact, for instance, with their mothers than female babies," Leyner said. "So what we're talking about are different ways of relating to people that start at the earliest possible age."
So can men say, "Honey, it's not my fault. It's my brain"?
"I like to use that excuse," Goldberg said.
Despite the book's title, the authors don't have an exact answer for why men fall asleep after sex.
"Science has not figured this one out. It could be that men are more often having orgasms during sex than, than women," Goldberg said.
Another gender myth: Women don't have Adam's apples.
"Well, that's another of these myths that's out there," Goldberg said. "Women do have Adam's apples. They're less prominent than men's."
Adam's apples are basically thyroid cartilage, which everyone has. Testosterone causes it to enlarge.
"Meg Ryan, Sandra Bullock -- they have larger Adam's apples," Goldberg said.
If a woman has a noticeable Adam's apple, it doesn't mean she has more testosterone than the average woman, according to Goldberg.
"It doesn't reflect on the testosterone levels," he sad. "Some people develop anatomically different and just happen to have a more prominent Adam's apple."
As for snoring, men do it more than women.
"There's a couple of reasons for that. One reason is that men tend to drink and smoke more, and that leads to more snoring," Goldberg said. "Women actually have a wider airway circumference, and that decreases the amount that they snore. Also, when men gain weight, they tend to gain it around the neck, and that weight around the neck also increases snoring."
Another common gender myth is that men cheat much more than women.
Studies show the cheating difference is now slight. Current research data says 80 percent of women remain faithful to their husbands, while 65 percent to 85 percent of men are faithful.
Women are catching up.
Although men often claim that they're better at driving, the jury is still out on whether men are better at this mechanical skill, but when it comes to safe driving, women are ahead.
Men are much more likely to get into accidents, killing themselves and others. Men speed more, drive drunk, run stop signs, and crash twice as often as women, research shows.
A World Health Organization study said, "Masculinity may be hazardous to health."
Study after study shows that men, especially young ones, take more risks than women. It is one reason women live five years longer.
But it's not the only reason, according to Goldberg.
"You still have heart disease," he said. "Heart disease tends to be the big factor that makes men die earlier, even once you get beyond the traumatic injuries."
Another reason is evolution, Goldberg and Leyner said.
"Women are evolutionarily around to prolong the species," Goldberg said. "They need to raise our children and to have our children."
Leyner said, "Men are basically sperm-dispensing machines and once they've done that, they're not as necessary."
Of course it's always bad to generalize.
"People are very afraid to say that men and women are different," Goldberg said.
Different can mean one is better, and many people don't want to hear that.
"There are differences that are genetic, and those don't necessarily mean that we're different and bad, that means that we're different and good," Goldberg said.