Modern videogames are obsessed with guns, and there are a lot of reasons why.

Shooters, shooters, shooters: Whether first-person like Halo or third-person like Gears of War, games that revolve around a player character taking aim and pumping bullets into rivals have been popular for decades, but the genre has grown vastly more popular in the last few years. In 2006, according to the NPD Group, shooters accounted for a substantial 14 percent of console game unit sales in the U.S. By 2011, that number had exploded to 24 percent.

Other game genres may be growing in popularity on smartphones and PCs, but on Xbox 360 and PlayStation 3 shooters are number one with a bullet. So it's no surprise that major publishers pump out more and more of them. But what is it that makes them so attractive in the first place? Do they fulfill some sort of adolescent male power fantasy? Well, yes. But that's not the whole story. Shooters, especially as designed today, have a way of worming their way into our brains and satisfying psychological urges that other game genres do not.

The act of firing a virtual bullet into another player's character is as old as videogames themselves. The first computer game Spacewar!, stored on paper punchcards and played on a computer the size of four refrigerators, was about two players moving and shooting at each other. The basics of the gameplay have hardly changed since then as the genre has become more refined, complex and realistic. And although many women play shooters, the genre has historically appealed mostly to men.

"Being ready to fight is an expectation of manhood," says sociologist Ross Haenfler. The author of Goths, Gamers and Grrrls: Deviance and Youth Subcultures says that studies of masculinity show that many boys and men feel as though they have something to prove. They want to give off, he says, "an aura of daring aggression."

"It’s difficult for most men to live up to that idealized version of masculinity," he says. "Videogames provide a space to safely engage in virtual violence.”

Certain types of games, Haenfler says, tap into men's psychological need to prove their masculinity by allowing players to "dominate" each other, defeating an opponent and making them look weak.

Shooter game design provides ample opportunity to do just that. In Halo, you can hear your opponents through your voice chat channel when they're close, the perfect venue for smack talk. The "kill cam" hovers over your body after you die, giving your opponent time to straddle and "tea bag" you.

Greg Goodrich, executive producer of Electronic Arts' upcoming Call of Duty competitor Medal of Honor: Warfighter, says his team is adding elements to the new shooter that will amplify the sense of competition.

Warfighter will allow players to join one of 12 different tier-one special forces units from around the world: The U.S. Navy SEALS, the U.K.'s Special Air Service, Germany's Gruppa Alfa. Goodrich says the idea came from an actual tier-one specialist who consulted on the game, who said that there was a "natural rivalry" between these units in real life.

Special forces members, Goodrich says, are “all alpha males... For them, the competition is very palpable and real.” Warfighter hopes to tap into a similar sense of team spirit and competition in its players.

Shooters are especially good at giving players a sense of autonomy, self-governance.This could easily apply, however, to all sorts of competitive games: sports, racing, monopoly. Why does the shooter seem to scratch this itch the best?

Scott Rigby, head of the gaming research company Immersyve and co-author of the book Glued to Games, says that shooters are particularly good at scratching a lot of psychological itches.

Shooters are good, he says, at giving players a sense of autonomy, or self-governance.

"You want to feel that if you're going down a path, you want to be going down that path," says Rigby, who studied behavioral science before founding Immersyve. The need to feel like you are in control of your actions is a psychological craving just as important as hunger or sleep, he says.

Another important need, Rigby says, is "relatedness" – feeling like you are connected with other people, that you have a material impact on each other.

Finally, he says, people crave competence and mastery. We aren’t happy doing the same easy, repetitive tasks in our day to day lives. We want to be challenged, to feel as though we are improving.

Shooters hit these needs better than other competitive game genres. Players of sports games have to rely heavily on the performance of their computer-controlled teammates – a reduction in their autonomy. Racing games just don't have that same sense of relatedness – you don't have as great an impact on the other players.

But in a shooter like Halo, you're making all your own decisions. And you're intimately related to the other player – you have to shoot him, and his only job is to shoot you.

The 2007 game Call of Duty 4: Modern Warfare made a major refinement to the shooter genre, one that vastly increased its satisfaction of that need for mastery and competence.

Taking a cue from role-playing games, Modern Warfare added a character-progression system. This kept players going by letting them level up, earning new gear and perks to improve their odds at success. This takes the need for competence and mastery and builds it into the game design, giving players more tangible and visible rewards for success.

Sure, these elements have existed in RPGs forever, making them quite addictive. But the steep learning curve is enough to keep many players away. In the end, the appeal of shooters above other genres of game is enhanced considerably by their accessibility. Anyone can do it; just point and shoot.