In 2009, a group of mostly white students were questioned about their political leanings and then shown three pictures of Barack Obama. The president's skin had been digitally lightened in one photo, darkened in another, and left completely unaltered in the last. The students were asked which image showed his "true essence." The liberal students were twice as likely to pick out the lighter picture, presumably because they believed "his true essence" meant "which picture looks like his soul is trying to leave his body." The more conservative students picked the darker one, unless they had actually voted for Obama, in which case they were also more likely to pick the lighter picture. Just in case the students were being influenced by the fact that Obama is a real person, the researchers ran another study with an image of a "racially ambiguous" fake politician and got the same results. This was presumably a photograph of Dwayne "The Rock" Johnson in a suit.

LatinContent WO/LatinContent WO/Getty Images
Seen here with his "racially ambiguous" 2016 running mate.

The research indicates that when you like or agree with someone, you tend to associate that person with having a lighter skin tone. When you disagree with them, you perceive them as being darker on the outside, as if all their internal negative qualities were somehow dirtying their outward appearance to warn you about their nefarious true nature. You might recognize that statement as the worst thing you have ever read.

The prejudice is so ingrained, we don't even know we have it, and it is getting worse -- weight discrimination has increased 66 percent in the past two decades. It starts early, too. A study in the U.K. found that kids as young as 4 assume that fat children have fewer friends, are less likely to be invited to parties, and are dumber than slim children, based on absolutely no knowledge of the children in question beyond their physical appearance. These same biases follow them into adulthood -- a separate study found that doctors who specifically treat obesity tend to think that fat people are lazy and stupid, findings that were presumably reinforced by the doctors' inclination to prescribe roller skates and book learnin' to their overweight patients.

Photos.com
"I bet that doofus tries to eat this on the way to the car."

Even more troubling, it turns out that male jurors, specifically thin male jurors, are more likely to convict an overweight person, especially if the accused is a woman (this is called "the Hamburglar effect," by us, just now). So just by being overweight, your chances of going to jail increase. People are also more likely to judge their bosses harshly and consider them less effective if they are overweight, even if their size doesn't affect their job in any way, and obese people (particularly obese women) actually earn less money than their colleagues. Considering that half the population is going to be staggeringly overweight within a few decades, we assume this prejudice is going to develop into fat people shunning slightly fatter people based on the size of their Rascal scooters rather than their actual waistlines.

In general, you are more likely to recognize objects through their individual pieces, but our brains seemed evolutionarily primed to see other humans as single entities, rather than a set of arms and legs. Except for women, whom we literally view as objects. We are more likely to be able to pick a woman's boobs out of a lineup than the woman herself. Since the researchers placed the blame squarely on the media and their use of the sexy bits of women to sell products, the best way to make sure you are treating women equally is to stare at a bunch of women's magazines in a newsstand at the airport and chant a firm mantra to yourself about not separating those ladies into parts. Try to blink as little as possible and be within earshot of a security checkpoint when you do this.

Normally when you look at a person, the part of your brain that controls empathy lights up. This helps you recognize that person's face and relate to what they are saying or doing, allowing you to interact with them as another human being because that is what people who aren't sociopaths do. However, when you look at inanimate objects, that area of the brain stays dormant, since there is no need to empathize with a book or a refrigerator or the first season DVD set of Star Trek: Deep Space Nine. A recent study conducted by researchers at Duke and Princeton universities found that the brains of participants looking at images of homeless people also didn't light up at all.

When looking at pictures of better-off men and women, the empathy part of the participant's brain lit up like the Fourth of July, but stayed as dark as a tomb for the homeless. Which means that, to them, homeless people were essentially the same as tables. Dirty tables.

Purple-Gecko/iStock/Getty Images
"Ugh, just toss it some quarters and maybe it'll go away."

Many of you have probably spent most of this article thinking that none of this applies to you, because your best friend is fat, you spend all your weekends volunteering at the soup kitchen, and you've never even seen Deep Space Nine. But none of that matters, because it is ridiculously easy to make you (and everyone else) biased about virtually anything. All you need to do is be put in a group for literally any reason at all, and you will automatically believe your group is superior to all others.

Jupiterimages/Stockbyte/Getty Images
"I'm just glad I fit into this entry instead of the earlier ones. What a bunch of assholes."

Simply telling people they are now in either Group 1 or Group 2 is enough to get them thinking about how much better their group is. You never actually need to meet the other members in your group; as long as you know you are in one, and that other people are in different groups, you will immediately start showing bias toward your group, even if that bias is causing you some immediately quantifiable detriment (such as getting banned from a PlayStation vs. Xbox message board or getting punched in the face during Trivia Night at Buffalo Wild Wings).

An obvious example of this is sports. On paper, it seems ridiculous that people would devote so much time and money to a bunch of strangers playing a game they have absolutely nothing invested in and no possible way of affecting the outcome. Yet people will tattoo their bodies, end friendships, destroy relationships, and even start freaking riots just to prove their team (or "group") is better than everyone else's. The groups don't even stay the same -- team rosters change, sometimes on a yearly basis. People aren't devoted to the people in the group, but to the idea of the group itself, and they will attack you (verbally or physically) for even daring to wear the shirt of a different group in their presence.

Fuse/Fuse/Getty Images
Everyone recognizes that this is crazy, right?

This is how malleable the human brain is. This is why we have been in a seemingly constant state of war for our entire existence. All you need to know is that there is an "us" and a "them" and you will automatically start doing whatever you can to make sure the "us" comes out on top.