" I stared at him. I said, “Wait, really? Like there’s an actual part of our brain that dictates how many people we can tolerate before we start acting like assholes?” “Congratulations, now you know the single reason why the world is the way it is. You see the problem right away—everything we do requires cooperation in groups larger than a hundred and fifty. Governments. Corporations. Society as a whole. And we are physically incapable of handling it. So every moment of the day we urgently try to separate everyone on earth into two groups—those inside the sphere of sympathy and those outside. Black versus white, liberal versus conservative, Muslim versus Christian, Lakers fan versus Celtics fan. With us, or against us. Infected versus clean. "

― David Wong , This Book Is Full of Spiders (John Dies at the End, #2)