Some experts blame evolution. It gave us minds that are vulnerable to emotional manipulation and prone to illusions, including the notion that we're usually thinking clearly and rationally. Evolution also saddled humanity with a complicated mating system, which allows politicians to push our buttons when they talk about sex, marriage, and birth control, which Santorum recently described as "not OK because it's a license to do things in the sexual realm that is counter to how things are supposed to be."
Most political ads are tapping into tribal instincts, said Michael Shermer, author of The Believing Brain, a book that deconstructs the roots of our beliefs in everything from ghosts to gods, 9/11 conspiracy theories to political rhetoric. Tribal instincts lead us to demonize rival groups, he said. It's not enough to say they're wrong on tax policy, said Shermer. "You need to label them as morally wrong, or evil, or really, really bad."
So you see people calling others immoral for allowing abortions, or birth control, or gay marriage. Shermer doesn't think social conservatives have any corner on irrational demonization, however. Liberals, he said, stereotype conservatives as greedy and selfish, yet conservatives consistently give more money to charity, even adjusting for income level. They also donate more blood.
The premise of Shermer's book is that evolution left the human race with a tendency to make what he calls Type 1 errors - false positives, or beliefs in things that don't exist. We also miss things that really do exist, which he calls Type 2 errors.
Evolution favors Type 1 errors because Type 2 errors are more likely to get you killed. If the grass rustles, and there's a possibility it's a lion, those who wrongly assume it's nothing make a Type 2 error and end up as evolutionary dead ends. Those who tend to err the other way and imagine a few lions that don't exist make Type 1 errors and survive.
Shermer concludes that evolution shaped us to be susceptible to figments of the imagination.
Elaborating on these Type 1 errors, Shermer describes a tendency to construct nonexistent patterns - "patternicity." Another chapter details what he calls "agenticity" - wrongly explaining accidental or natural occurrences as the conscious action of an agent.
For a professional skeptic and founder of Skeptic Magazine, Shermer is surprisingly forgiving of Type 1 errors. People who make a lot of these aren't necessarily stupid, he said. Creative people can be particularly prone to patternicity, he said.
One striking example is Nobel-winning biochemist Kary Mullis. The two met at a social event, during which the Nobel laureate regaled Shermer with his enthusiastic embrace of astrology, ESP, several AIDS-related conspiracy theories, and his close encounter with extraterrestrials. Most people would find an excuse to get away, but Shermer was intrigued.
The Nobel committee made no mistake. Mullis won his prize for one of the most important discoveries in biology - a technique for multiplying strands of DNA that has become essential in all kinds of biomedical research and DNA forensics. Mullis reports that he had the key insight while driving over the Santa Monica hills. There, a vision struck him - a pattern in DNA that he could exploit.
If we all suffered from the same illusions and delusions, we might not be so polarized on the political spectrum. But our peers, families, and inborn tendencies tend to pull people in different directions.
Some people feel a deep resonance with Rick Santorum's opposition to contraceptives and gay marriage. Others see it as crazy. But what if he were talking about marriage among brothers and sisters? Or polygamy? Shermer said most people are subject to an instinctive sense of "how things are supposed to be," though they may come up with rational justifications after the fact - sibling marriages might lead to more birth defects, for example, or group marriage would allow exploitation of women.
These sex-related issues stir up particularly strong feelings that some attribute to evolution as well. Humans don't agree on "the way things are supposed to be" in sexual matters because we humans don't have a consistent mating strategy, said University of Pennsylvania evolutionary psychologist Rob Kurzban. Most other animals mate in predictable patterns, whether it's the monogamy of the penguin or the promiscuity of the chimpanzee. For us, a combination of genetic, environmental, and cultural factors leads some people to be completely monogamous and others to mate with hundreds of people.
Why should any of us care what other people are doing? The monogamous people are most successful in a culture where everyone else is monogamous, said Kurzban. If the rules change, their partners get more chances to cheat.
One of the most popular human mating strategies is to have a faithful partner, lie to that partner, have lots of sex with other people, and then make public statements judging others for being promiscuous.
Kurzban explains why this is so successful in Darwinian terms in his book, Why Everyone (Else) Is a Hypocrite. Our brains aren't necessarily wired for consistency, he said. The part that dictates personal behavior isn't as well-connected as we think to the part that judges the behavior of others.
"Morality is strategic," he said. Most people choose moral values that help them, whether it's powerful people favoring rules that preserve their power, or promiscuous people fighting to preserve their more freewheeling behavior.
Shermer agrees that either way we swing, we may be less rational than we think when we're considering morality and politics. "We gravitate to the party that feels right and then employ our brains to find reasons," he said.
Contact Faye Flam at 215-854-4977, email@example.com, on her blog at www.philly.com/evolution, or @fayeflam on Twitter.