For as long as humans have claimed territories, we’ve been faced with the need to defend them. The most proactive defense is to make boundary lines obvious so that potential competitors believe that crossing them will result in dire consequences. Tigers scent-mark their territories with urine and feces. The crows in my yard voice a special territorial clamor. And humans? The variety of boundary markers we deploy defies enumeration.

I subscribe to the typical Western pattern. A stranger approaching my territory would note first a hedge growing between the public sidewalk and my shelter. Then steps ascending to a roofed porch. And finally a door. The nearer he got to the core area, the more solid the defenses would appear. As I approached this stranger from inside, I could assess him through the glass door before deciding whether to release the lock.

If a hostile human did penetrate my defenses, I’d probably react like most other territorial animals. Imagine that you have discovered a stranger in your shelter. If the invader is a good distance away, you will likely flee. If the invader is close enough that your flight would attract his attention, you might opt to hide (a “freeze” response is more common in other species). Closer still, and your options will narrow. You’ll be forced to confront the invader and issue a defensive threat. A cornered raccoon would hiss and growl; you might scream or grab a kitchen knife. Finally, if the invader is close enough to render all these options moot, you’ll attack like the proverbial cornered beast. But that’s the least appealing option, and the riskiest, for any species. Given the chance to escape, most will jump at it.

Human females, especially, strive to avoid a fight. In a recent study of the two sexes’ response to various threats, the difference was stark. Females were more likely to flee or hide at the first sign of trouble. Given the same sign — a stranger jumping out from behind a bush — males were more inclined to investigate the situation, or seek a weapon. Overall, females were much quicker to shout for help, too.

Happily, not every attempted invasion leads to such a showdown. Usually, competitors have a chance to size each other up before committing to an invasion or defense. If I look out my door and spy a peddler of life insurance or religion, my frown or hand-flap is usually aggression enough to rebuff the invader. If the invader is an unfamiliar or seems menacing, I’ll retreat to my core area and spare myself a fight.

Just what chemistry causes a female like me to act more or less territorial isn’t known. Laboratory experiments with rodent mothers suggest that nursing her offspring causes chemical changes in a mother’s brain. So perhaps those changes allow breeding females to put aside their fear when their offspring need a champion. But many females are territorial even without offspring to inspire them. The famously aggressive hyena females take the lead in marking the clan’s territory, patrolling it against trespassers, and launching strikes against neighbors. In monogamous klipspringer antelopes (Africa), it’s also the female who attends to the boundary-marking chore. Even the oriental fruit fly will guard the peach on which she lays her eggs.

In addition to defending my core area, I also maintain a bubble of space that surrounds me wherever I go. I feel it bump up against competitors when I stand in line at the grocery store, and my bubble shudders with irritation when another driver cuts in front of me or follows too near behind. In fact, one of the seminal studies on human territoriality focused on drivers. In 1997, a sociologist measured the time it takes for a driver at a shopping mall to vacate a parking space. He found that a human takes seven seconds longer when another human is waiting for the space. And if the waiting human blasts his horn, the occupant will defend the temporary territory for an additional twelve seconds. This shocked me, as a human who often hustles to accommodate my fellow humans. Even more shocking was this detail: males (and only males) will actually abandon a territory more quickly if the intruder is driving a more expensive car. Females are either unimpressed by such status displays or, like me, they don’t know their Alfa from their Edsel.