Rabbi Sacks penned an op-ed for the New York Times today, arguing that religion was and is evolutionarily adaptive because it strengthens the group bonds that give rise to altruism, and therefore is a Good Thing.
Minor point: I thought it was interesting that in his list of "New Atheists," Sacks leaves out Dan Dennett, who wrote an entire book arguing that religion may have served an evolutionarily adaptive function.
Anyway, here are my thoughts. I actually don't disagree with him that religion strengthens group ties, and I think it's possible this offered survival benefits in the past. (Of course, religion is not a precondition to group living, and it is group living that is probably the key to the evolution of altruism. Many non-human primates live in social groups with cooperative ties, and as far as I know, they don't attend church or shul.)
But, there is a side he ignores. Religion is not just group-oriented--it is usually tribalistic. There is intense concern and strong altruism towards one's group, but often less concern--if not apathy or derogation--towards other groups. (A friend of mine recently told me a story about when he was in a modern orthodox high school and formed a group to raise awareness of ethnic cleansing in Darfur. A school rabbi expressed clear disapproval to him, because his time and effort could instead be used to help poor Jews in Israel.)
There is much evidence that social groups influence prosocial reactions, and the stronger the tribalistic ties within a group are, the more apathy or derogation will tend to arise towards other groups, or even to those seen as "black sheep" within one's group. (See: the Spanish Inquisition, or Rabbi Nuchem Rosenberg being doused with bleach for speaking out against sexual abuse, thus betraying his community's norms.)
The point is, religion may have been adaptive in the past. But adaptiveness of a trait depends on the current environment--so this does not tell us whether religion is adaptive in a globalized world, in which countries are pointing nuclear weapons at each other. Rabbi Sacks cannot extrapolate from one to the other. In a world in which Syria's biological and chemical weapons might become up for grabs, does religious tribalism prove maladaptive in a way that outweighs the benefits of tight-knit religious communities? What about the ideology and norms that serve as a bedrock for communal interaction and trust, but may lead to discrimination against women and gay people?
Put more simply, most atheists probably recognize there are warm benefits of religion and religious communities. The question is, are the costs of tribalism and ideology even greater? And, are there ways to gain the social benefits of these types of communities while removing the ideology and tribalism? After all, one doesn't need a very tight-knit community to be altruistic and prosocial. If we face a tradeoff--communities that are less cohesive and committed, but which come with less tribalism--it is worth considering.