The conventional wisdom is often wrong.

But a mountain of recent evidence suggests that teacher skill has less influence on a student's performance than a completely different set of factors: namely, how much kids have learned from their parents, how hard they work at home, and whether the parents have instilled an appetite for education.

Think about all the time, brainpower, and social or political capital you continued to spend on some commitment only because you didn't like the idea of quitting.

Over time, some ideas do cross the repugnance barrier to become reality. Charging interest on loans. Selling human sperm and eggs. Profiting from a loved one’s premature death. This last example of course describes how life insurance works. Today it is standard practice to wager on your own death in order to provide for your family. Until the mid-nineteenth century, life insurance was considered “a profanation,” as the sociologist Viviana Zelizer writes, “which transformed the sacred event of death into a vulgar commodity.

When Al Gore urges the citizenry to sacrifice their plastic shopping bags, their air-conditioning, their extraneous travel, the agnostics grumble that human activity accounts for just 2 percent of global carbon-dioxide emissions, with the remainder generated by natural processes like plant decay.

But as history clearly shows, most people, whether because of nature or nurture, generally put their own interests ahead of others’. This doesn’t make them bad people; it just makes them human.