You know you're supposed to act differently around your boss than you do around your colleagues, and if you've ever watched a group of dogs interact, you'll see that they have a social order, too.
There's a "top dog" that's in charge, and the others know their place.
Monkeys and other animals have rules about who does what, too. It's called the social hierarchy. And it has a huge influence on us -- on how we act, whom we spend time with, even where we go and what we buy.
Now, researchers have found evidence that our brains may actually be hard-wired for hierarchy. And in fact, we may be wired to value the "top dog" over the people who rank below us.
To understand how our brains process social ranking, Caroline Zink, a neuroscientist at the National Institute of Mental Health, and her colleagues set out to capture images of the brain while having volunteers play a simple computer game.
The researchers looked for differences in brain activity after volunteers were told they were "superior" or "inferior" to others playing at the same time.
"I actually did the analysis twice because I couldn't believe how strong these differences were," Zink said. "It was striking."
The study, published today in the medical journal Neuron, involved placing volunteers in a special MRI scanner. As each person played the computer game, the researchers were able to see what parts of the brain were most in use. They told the volunteers that someone else would be playing the game at the same time and that the other person was either more- or less-skilled.
The researchers made it clear this was not a competition: Players earned a dollar for each correct response, no matter what the other person did. Although the volunteers were shown a photo of the other player, they were really just playing against a computer.
While some parts of the brain always "lit up" no matter who the volunteers thought was playing, an additional pattern emerged when the players thought their opponent ranked higher than they did.
One area that became more active in volunteers facing a higher-ranked player was the ventral striatum, a part of the brain that responds to money and rewards. Essentially, it recognizes things that are of value to us.
The brain activity suggests that players not only placed more value on the superior player, but even cared more about that person.
Another active area in the same scenario was the occipital parietal cortex, which processes vision and attention.
"We pay more attention to the superior person than the inferior person," Zink explained. "We see that in primates, too. They spend more time looking at the dominant monkey than at the inferior or submissive one."
Volunteers' comments also showed they were paying more attention to the higher-ranking player, as they would comment on that person's appearance, even remembering their hair color.
Conversely, the volunteers didn't say much about the lower-ranking players.
Because social rank is so important, you might think our brains would spend a lot of effort figuring out where people stand. And in fact, although the brain doesn't exactly create social status, certain regions do seemed to be wired to interpret it.