Once when I was a little kid, a peaceful fall evening at our house was shattered by loud and insistent banging, as if someone was trying to break down our side door. My dad, who was the head coach of the high school football team, opened it to greet a man who was screaming with fury. Despite the fact that he was a friend of my father's, this man was now beside himself with rage, drunk, practically incomprehensible, spitting foam and bellowing invective. My dad’s friendship-destroying crime? He had switched the man’s son from first string to second string on the team. 
We Americans take our football seriously. For many people, whether their team has won or lost is the bellwether for happiness, and few cultural institutions engender such intense loyalties and equally passionate rivalries and controversies. Take, for example, the fervor and furor over Denver Broncos quarterback Tim Tebow, who kneels and prays on the field, wearing his devotion to Christ very publicly. Or the over 50 thousand Detroit Lions fans who have signed a petition against the Canadian band Nickelback playing a Lions halftime show just because they’re not from Detroit. Or even the tragic allowance and cover up Penn State colleagues made for Sandusky’s alleged penchant for sexually molesting little boys. What is it about football that brings out such intense team loyalty in us?

The human ego is composed primarily of a constantly shifting medley of body sensations and thoughts combined with snippets of autobiographical memory (according to neuroscientist Antonio Damasio). But there is more to the self than just our own personal history and experience. Human beings evolved as social organisms. Going back over four million years, our ape ancestors learned to survive as a group, and as humans evolved we inherited and continue this behavior pattern. Our ego evolved to include the other members of our tribe as an extension of the self, as a part of “me.” The group was absolutely vital to survival, and usually composed of genetically-related individuals, so this sense of “I am my tribe” was selected for and runs very, very deep in us. It is a strong, visceral sense of connectedness that is the heart of our need to belong

 In the modern world, our social organizations are much larger and more complex than the little tribes that roamed the ancient savanna, but our brains respond to group identity in much the same way. You might “be” a Trekkie, or a Hoosier, or a Republican, and that identity might mean as much to you or more than your family ties, your sense of national pride, or your religious beliefs. Certainly one of the stronger, more emotionally intense identifications many people in our society have is with their favorite sports team. Researchers from both the University of Georgia and the University of Utah measured the testosterone levels in male fans before and after sports events, and found a 25 percent boost when their team won, and an equal dip for the losers. Our identification with our team is nothing more than a mental construct (the connection is not literal) and yet it affects us at the deepest physical levels. Charles Hillman, a University of Illinois psychologist found that fans watching their team experienced extreme levels of physical arousal—demonstrated by changes in heart rate, brain waves, and perspiration.

So why do fans care so much—whether pro or con—about Tebow’s religious affiliation? Probably because it divides the in group into uncomfortable, opposing sub-groups of believers and non-believers; it’s a schism in the tribal band. Lions fans are so identified with being Detroiters (a group that includes a lot of famous musicians) that hiring a band for the halftime show that doesn’t represent the city is tantamount to treason. And, on the dark side, our tribal and group bonds—which make the actions of group members psychologically equivalent to our own actions—motivate us to cover up the flaws of our important team members, which can lead to heartbreaking errors in judgment that leave children damaged for life. All of this is underpinned by the ancient hunter-gatherer urge to bond with the tribe, and to pull together as a team for survival.

So as you are striving to digest a bellyful of turkey, mashed potatoes, and gravy, and notice yourself screaming at the television, enraged at a bad call by the ref, or jubilant at a touchdown, remember that millions of years of human evolution have shaped your brain to emotionally bond with your team. Emotionally, the outcome of the game is as important as the meal you've just consumed. As far as your Stone Age brain is concerned, you are your football team.