THE REPUBLICAN PARTY IS BASED ON THE ANGELS OF OUR BETTER NATURE...:

The human mind's propensity for us-versus-them thinking runs deep. Numerous careful studies have shown that the brain makes such distinctions automatically and with mind-boggling speed. Stick a volunteer in a brain scanner and quickly flash pictures of faces. Among typical white subjects in the scanner, the sight of a black man's face activates the amygdala, a brain region central to emotions of fear and aggression, in under one-tenth of a second. In most cases, the prefrontal cortex, a region crucial for impulse control and emotional regulation, springs into action a second or two later and silences the amygdala: "Don't think that way, that's not who I am." Still, the initial reaction is usually one of fear, even among those who know better.

This finding is no outlier. Looking at the face of someone of the same race activates a specialized part of the primate brain called the fusiform cortex, which recognizes faces, but it is activated less so when the face in question is that of someone of another race. Watching the hand of someone of the same race being poked with a needle activates the anterior cingulate cortex, a region implicated in feelings of empathy; being shown the same with the hand of a person of another race produces less activation. Not everyone's face or pain counts equally.

At every turn, humans make automatic, value-laden judgments about social groups. Suppose you are prejudiced against ogres, something you normally hide. Certain instruments, such as the Implicit Association Test, will reveal your prejudice nonetheless. A computer screen alternates between faces and highly emotive terms, such as "heroic" or "ignorant." In response, you are asked to quickly press one of two buttons. If the button pairings fit your biases ("press Button A for an ogre's face or a negative term and Button B for a human face or a positive term"), the task is easy, and you will respond rapidly and accurately. But if the pairings are reversed ("press Button A for a human face or a negative term and Button B for an ogre's face or a positive term"), your responses will slow. There's a slight delay each time, as the dissonance of linking ogres with "graceful" or humans with "smelly" gums you up for a few milliseconds. With enough trials, these delays are detectable, revealing your anti-ogre bias--or, in the case of actual subjects, biases against particular races, religions, ethnicities, age groups, and body types.

Needless to say, many of these biases are acquired over time. Yet the cognitive structures they require are often present from the outset. Even infants prefer those who speak their parents' language. They also respond more positively to--and have an easier time remembering--faces of people of their parents' race. Likewise, three-year-olds tend to prefer people of their own race and gender. This is not because children are born with innate racist beliefs, nor does it require that parents actively or implicitly teach their babies racial or gender biases, although infants can pick up such environmental influences at a very young age, too. Instead, infants like what is familiar, and this often leads them to copy their parents' ethnic and linguistic in-group categorizations.

Sometimes the very foundations of affection and cooperation are also at the root of humankind's darker impulses. Consider oxytocin, a compound whose reputation as a fuzzy "cuddle hormone" has recently taken a bit of a hit. In mammals, oxytocin is central to mother-infant bonding and helps create close ties in monogamous couples. In humans, it promotes a whole set of pro-social behaviors. Subjects given oxytocin become more generous, trusting, empathic, and expressive. Yet recent findings suggest that oxytocin prompts people to act this way only toward in-group members--their teammates in a game, for instance. Toward outsiders, it makes them aggressive and xenophobic. Hormones rarely affect behavior this way; the norm is an effect whose strength simply varies in different settings. Oxytocin, however, deepens the fault line in our brains between "us" and "them."

Put simply, neurobiology, endocrinology, and developmental psychology all paint a grim picture of our lives as social beings. When it comes to group belonging, humans don't seem too far from the families of chimps killing each other in the forests of Uganda: people's most fundamental allegiance is to the familiar. Anything or anyone else is likely to be met, at least initially, with a measure of skepticism, fear, or hostility. In practice, humans can second-guess and tame their aggressive tendencies toward the Other. Yet doing so is usually a secondary, corrective step.

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