Humans are an instinctively tribal species. And while this trait served us extremely well throughout our long history, we have not only outgrown its usefulness, but are now victim to its destructive influence. Of all the arguments employed by Harris, Dawkins, Hitchens, et al to challenge the usefulness of religion, one is largely overlooked: the way religion feeds our tribal instinct. To his credit, Penn Jillette touches on the issue in the afterword of his new book "God, No!"
Compared to other animals, humans exhibit extreme "groupishness." We are unusually co-operative with, even altruistic toward, in-group members. And on the flip-side, we are distinctly suspicious of out-group members. We suspect their habits, motives and values, and even question their intelligence. Our apprehension is extreme: while a small number of animal species display occasional viciousness, their aggression is nowhere near the scale of human righteousness, warfare or terrorism.
In explaining the tribal nature of Homo sapiens, evolutionary scientists collectively share the view that within-group co-operation improves the survival rates of its members, who, for example, would be hard-pressed to succeed as independent hunters. In a harsh environment with limited resources, it is highly adaptive to be both pro-social within our tribes and anti-social to outsiders who compete for food and mates. We have been hunter-gatherers for more than 99 percent of our history as a member of the Homo genus, and for 90 percent of our time as the sapiens species of this genus. So what worked for our progenitors has been deeply hardwired into who we are today.
But the out-group hostility element of tribalism is no longer adaptive in the modern, complex form of civilization we have created. We are now more interdependent as a species than ever before, by virtue of our interconnected economies, our real-time, Internet-based communication, the power of our weaponry and the environmental influence of our industrial activity. The benefit of out-group hostility has not only expired, but is now severely detrimental to our well-being both as individuals and as a species. We should be working hard to defy our impulse toward out-group hostility. And this is precisely the problem with religion -- it feeds the very instinct that we should be resisting.
While religion promotes the in-group, prosocial side of tribalism, it also fosters the out-group, anti-social side. The out-group feature of religion is uniquely problematic: faith separates people in a deep, fundamental way. Faith-based belief systems are absolutely incommensurable. Different faith-based convictions cannot be reconciled because there is nothing to appeal to in order to understand, challenge or share them. Either you have a certain form of faith or you don't -- there is no rational way to reconcile different views of reality. Religion not only promotes difference, it makes divisions impossible to eliminate, so between-group co-operation is discouraged and out-group hostility is fueled. Jillette makes the point that "the only argument against religious terrorism is to try to share the reality of the world." And he points out that faith separates us since it means that "anything goes." Indeed, a shared sense of reality is the only valid starting point for reducing our tribal instincts.
When it comes to purely practical arguments, atheists and theists can argue whether it has been religious zealots or monomaniacal non-believers who have killed the greater number of people over the course of history. The discussion usually degenerates into whether Hitler was an atheist or a Catholic (probably both -- madmen are not deterred by contradiction). But the more relevant argument is that religion promotes out-group mentality in an age of interdependence when we can't afford to surrender to ancient instincts. Just as we have to resist our ancestral urge to eat sweet, fatty foods -- an instinct that once served our survival but now threatens our well-being in a world where sugar and fat are abundant -- we also have to resist the urge to indulge in the tribalism that religion promotes. Our greatest opportunity as human beings is also our toughest challenge: to defy our maker. Not the faith-based, mystical one, but the natural selection one, which shaped who we are in an environment that was much different than the one in which we now live.