Most men begin to straighten their posture, adjust their clothes, and even clear their throats in front of attractive women. The mere presence of, or thinking about, women can cause men to behave differently in unexpected ways. Researchers at the University of Utah in Salt Lake City found when there's an abundance of women, men are more likely to be sexually promiscuous and violent.

Men become less focused or committed to single partners, and show interest in pursuing multiple relationships when there's a surplus of women, which increases aggression. An abundance of women means men become less preoccupied with choice, and adopt promiscuous behaviors that inevitably bring conflict and crime.

“This brings men into conflict with each other in response to their more uncommitted, promiscuous mating orientation," Ryan Schacht, author of the study, of the University of Utah in Salt Lake City told New Scientist.

However, when men outnumber women, they're more likely to commit fewer crimes and infidelities. Rather, they shift their attention toward being more dutiful to win and keep a partner. Here, men alter their behavior to comply with "supply and demand" conditions. When women are rare, men see them as a valued resource. This gives women more "bargaining power over what they expect from a relationship,” according to Schacht.

In the study, published in Human Nature, researchers came to this conclusion by analyzing sex ratio data from the US Census Bureau for all 3,082 US counties in 2010, and contrasting it with crime data from the US Federal Bureau of Investigation, which lists women and men 15 to 45 years old from the same year.

In the counties where the men outnumbered the women, there were lower rates of murders and assaults as well as fewer sex-related crimes, including rapes, sex offenses and prostitution. In other words, there were fewer crimes in counties predominantly male. This held true even when researchers accounted for other potential factors, such as poverty.

Men are less likely to act out of haste when there's a low supply of women.

“In some situations they will be much better behaved, and in others they will be much more prone to nasty behaviour,” Schacht told New Scientist.

This challenges the conventional belief male excess can lead to higher levels of violence. These findings do have implications for crime prevention. The researchers suggest crime prevention should focus on places with more women, where men are more likely to act out on aggression and malice.

So, how else do women influence behavior in men?

Men become less intelligent when being observed by women

The IQ levels of men tend to drop when they believe they're being observed by a woman. In a 2009 study, researchers asked men to perform a Stroop test — where the name of a color appears on the screen in a font that's a different color. After taking the test for the first time, the participants were then asked to pronounce a series of Dutch words in front of a webcam; this was known as a lip-reading exercise. The researchers made them believe there was a person watching them via webcam by giving them the person’s name. However, the participants couldn’t see. Those who believed they had been observed by a woman during the lip-reading test, performed worse the second time taking the Stroop test.

Men feel less happy about their relationship when meeting pretty women

Men tend to feel worse about their relationships after they encounter a pretty woman. In the 2010 study, people interacted with strangers of the opposite sex; sometimes their partners were attractive, other times they were seen identified as average-looking. The participants were then asked to evaluate how they felt about their romantic relationships. Men generally reported feeling less satisfied with their relationships after being exposed to attractive women.

Men become impatient around attractive women

Unsurprisingly, men who stare at a pretty woman will display less patience and willpower. In the study, participants were asked to either receive a small sum of money tomorrow instead of a large one in the future after viewing pictures of attractive or unattractive members of the opposite sex. Men who looked at pictures of attractive women were more likely to choose the small sum of money compared to the men who saw the unattractive women.

Men take more risks in front of women

Men are more likely to take risks in front of women. A 2010 study found when groups of young men were skateboarding, they tended to play it safe and sane. However, when good-looking women came to observe the skateboarders, they took more risks and tries more impressive moves. Men wanted to exert their male dominance in front of these women.