As SCOTUS debates the constitutionality of Proposition 8 and DOMA this week, Facebook users all over the nation have become part of a burgeoning social media trend. Supporters of marriage equality have been changing their profile pictures to the icon on the left, a version of the Human Rights Campaign logo designed specifically to indicate support for same-sex marriage rights.

Although many people have said that it's been personally meaningful to sign onto Facebook and see a screen full of red avatars, many have criticized the trend for being a silly way of "showing support" without actually accomplishing anything significant. However, although the SCOTUS justices might not be checking Facebook to tally up the red avatars before rendering a decision, a demonstration of solidarity like this one really could end up making an impact.

The reason why those avatars might actually make a difference has to do with the fact that at the end of the day, there's a part of our brains that never quite made it out of high school. Namely, we're all too susceptible to the powers of peer pressure, or social proof. Our friends, family, and the people around us exert strong influences on our attitudes and behavior, whether intentional or not.

One of the big ways that the people around us exert these influences is through the use of norms, those messages that we send out about what's acceptable, appropriate, and...well, normal. Descriptive norms simply describe the way that things are, whereas prescriptive norms offer a mandate about how things should be. For example, if I said that most college students go to class wearing jeans and sweatshirts, that would be a descriptive norm. If I said that you should wear jeans and a sweatshirt in order to fit in, that would be prescriptive. Quite possibly the most important takeaway point from all of the research that's been done on norms is just how powerful descriptive norms can be. When people try to change behavior, they often focus on prescriptive norms, telling people what they should do. We often underestimate just how strongly we respond to what other people actually do.

In a classic study, Cialdini and colleagues manipulated the signs that were displayed in Arizona's Petrified Forest National Park, a site often plagued by tourists who end up grabbing some of the petrified wood to take home as a souvenir. In situations like this, the first inclination of well-meaning environmentalists might be to set a strong prescriptive norm -- perhaps by saying something like, "Many past visitors have removed the petrified wood from the park, changing the state of the Petrified Forest. This is bad, don't do this." The idea here would be to invoke a sense of shame and severity before asking visitors to refrain from taking the wood. But read that prescriptive message once again. Is there anything descriptive in there? Yes, of course there is. That message is not just telling you that you shouldn't take the wood -- it's also telling you that most other people do. In fact, people were actually more likely to steal wood from the forest when they saw the sign telling them how many people tend to do it themselves, even though the very next sentence was asking them to refrain. But when the researchers simply tweaked the message to read that "the vast majority of past visitors have left the petrified wood in the park, helping to preserve the natural state of the Petrified Forest," the thievery plummeted.

We don't really care so much about what we should do. We care about what other people do. And then we really, really care about not being different.

We see this happen all of the time in the world around us. Have you stayed in a hotel lately? If you have, then you've probably seen the little cards requesting that you re-use your towels to help conserve water. Well, as you can probably guess by now, the wording on those cards actually matters. Simply telling travelers that the majority of guests reuse their towels is more effective at getting them to re-use their own than a prescriptive plea asking guests to help protect the environment.

If you go door-to-door soliciting donations for your charity, simply presenting a longer list of existing donors will increase the odds that the next person you approach will actually donate. After all, if most people tend to donate, you certainly don't want to be the only one who doesn't. This is why bartenders and baristas will "salt the tip jar" by putting in a few dollars of their own before their shifts begin. People will give more if they think that it's "normal" to do so.

If you are given five positive reviews about a book, you will rate the book more favorably if you hear the five reviews coming from five separate voices than if you hear all five of the same reviews coming from the same voice, even if the information that you're getting is exactly the same. Why? Because the more you see a wide variety of people doing, endorsing, or believing something, the stronger that descriptive norm becomes -- and the more likely you are to make sure your attitudes or behavior match up.

And even though most people report that they find TV shows with laugh tracks to be incredibly annoying, they will end up laughing more when they watch shows that have them, and will go on to rate those shows as having been funnier. Why? Because without even realizing it, the sheer act of hearing other people laugh throughout the half-hour program -- even if you consciously know that the laughter was fake -- sends a message to your brain that it is "normative" for people to find that content funny.

Which brings us back to Facebook. When looking at the literature on descriptive norms and social proof, there's one finding that consistently pops out - the more targeted the norm, the more effective it is. For the towels, referring to the majority of past guests who stayed in that room has a stronger effect than referring to the majority of past guests who stayed at that hotel. For the door-to-door charity, the effect on donations was even stronger when the names on the list of prior donors were people that the potential new donor actually knew, like close friends or neighbors. We don't just respond to descriptive norms -- we respond particularly strongly to descriptive norms set by the people that we care about. Which, presumably, includes the people (or at least, some of the people) that we are linked to on Facebook.

People look at an issue like marriage equality, and the first inclination is to set prescriptive norms. We should do something, the justices should rule a certain way, you should support a given cause. But based on everything that we know about our brains and their bafflingly strong desires to fit in with the crowd, the best way to convince people that they should care about an issue and get involved in its advocacy isn't to tell people what they should do -- it's to tell them what other people actually do.

And you know what will accomplish that? That's right. Everyone on Facebook making their opinions on the issue immediately, graphically, demonstrably obvious. That is literally all that it takes to create a descriptive norm: Publicly acknowledging your belief along with the thousands of other people who are also publicly acknowledging theirs.

So, no. The fact that you've replaced that picture of yourself mugging for the camera with a red square and an equal sign will not cause Justice Kennedy to bang his gavel or stomp his foot and say that he's come to a final decision on the matter, and that it's all because of your new profile picture. Changing your Facebook image will not have a direct impact on our legislation.

But a widespread descriptive norm implying that it is socially acceptable to advocate for same-sex marriage and that most people in contemporary American society seem to be pro-marriage-equality?

Now that just might.

Platow, M., Haslam, S., Both, A., Chew, I., Cuddon, M., Goharpey, N., Maurer, J., Rosini, S., Tsekouras, A., & Grace, D. (2005). “It’s not funny if they’re laughing”: Self-categorization, social influence, and responses to canned laughter Journal of Experimental Social Psychology, 41 (5), 542-550 DOI: 10.1016/j.jesp.2004.09.005

Lee, K. (2004). The Multiple Source Effect and Synthesized Speech. Human Communication Research, 30 (2), 182-207 DOI: 10.1111/j.1468-2958.2004.tb00730.x

Cialdini, R.B. (2001). Harnessing the science of persuasion. Harvard Business Review, 79, 72–79.

Cialdini, R.B. (1993). Influence (3rd ed.). New York: HarperCollins.

Image of the HRC equality logo via Wikimedia Commons, designated as a public domain image.