Next time you are in front of a building with a steady crowd going in and out, sit back and watch for a few minutes. Some people hurry through the door. Others hold the door for the people behind them. What makes you decide to hold the door for the people behind you?
There are lots of possibilities, of course. It might be that it is a personality trait. People who are conscientious might be more prone to hold the door for the people behind them. Another possibility is that there is a social component. Perhaps men are socialized to hold the door for women or young people hold doors for older people. Maybe that social component isn't so altruistic. Maybe men hold doors open for women hoping to seem more attractive to them. It is also possible that it is just a habit. If there is someone behind you at a particular distance (say 5 feet), then you hold the door, otherwise you don't.
While it is possible that all of those could be true to some degree, a paper in the May, 2011 issue of Psychological Science by Joseph Santamaria and David Rosenbaum suggests that you also hold the door open for people behind us to minimize the collective effort spent.
Now, clearly, you hold the door for people behind you, because it makes it easier for them. They do not have to take the effort to open the door. If everyone held the door if there was someone close behind them, then over time, you would have the door held open for you about as often as you held the door for others, and overall everyone would spend less effort opening doors.
How could you test this, though?
The authors got video of 148 people approaching a door and measured whether they held the door for people behind them. They did some clever analyses of these data.
First, they tested the habit idea. If there are two people walking behind you, then it should be easier to see them from a distance than if there is only one person behind you. They certainly found that the further behind the second person or pair, the less likely you are to hold the door. But, it did not matter whether there was one person behind you or two.
However, if there are two people behind you, you might be willing to hold the door for a longer time. That is, when you are minimizing effort for a larger group of people, you might be willing to hold the door for a longer period of time. That was the case. People held the door for a shorter period when there was one person walking behind than when there were two people walking behind.
So far, so good, but what about the behavior of the people who are following?
The idea that people are minimizing effort suggests that part of the responsibility for minimizing effort rests with the followers. If you see someone holding the door open for you, and they are trying to minimize effort, then you should speed up.
That is what happens. If the person in front holds the door, the person behind walks faster. Interestingly, though, a single person walking behind speeds up more than a pair of people walking behind. It is almost as though when one person holds a door for a second, both parties need to share equally in minimizing effort. When one person holds the door for a group behind them, the door holder's effort is outweighed by the effort of the group walking behind.
I'm not saying that we are making this calculation consciously. I do think we have a habit to open perform social graces like opening doors. However, these cultural practices succeed, because they help people to minimize the collective effort that needs to be spent on daily tasks.
In some ways, this is just a cultural version of the golden rule. If everyone does things for others that they would like to have done for them, it ultimately makes everyone's life a little better. And these little things add up over time.
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