Yet something happened the other day that made me think I have been too hard on my students. I often try to describe to them the way their ancestors, not all that long ago, would have chosen the mates of their children, a practice they associate today with some backward part of India. I try to help them see that the choice of a marriage partner should be based on wider considerations than romance alone. To focus this discussion, I ask them a hypothetical question. Suppose you were to be guided in your selection of a wife by one, and only one, of two factors, either your hormones or your parents. That is, would you let your parents pick your wife or would you rather trust your sensual desire, that spark of attraction that makes you light up with sexual longing?

In past years, my students were horrified at the thought of their parents choosing their marriage partners. This year was different. Many of them said they would trust their parents. In fact, more said they would trust their dads than their moms. They thought their moms would look for a good girl and disregard looks altogether, while they thought their dads would probably get the balance of moral and physical attributes just about right.

I found their conversation to be very moving, and wondered if my two young boys, when they reach the marrying age, will have that kind of trust in me. We lose something when we do not have to fight for what we believe, but what we have gained in father and son relationships is so much more important that I do not regret that my boys will never be able to relate to Cat’s in the Cradle.

In a pre-Christmas poll last year of religious Christians with kids age 2 to 18, 78 percent said they’d bought DVDs of movies or TV shows for their teenagers, and 87 percent said they’d bought these for kids 13 and under. “However, one-quarter of those adults (26 percent) did not feel comfortable with the DVD products they bought.” Likewise for music CDs: “About six of 10 parents bought these discs for their kids, yet one out of every three of those parents (33 percent) had concerns about the content.” As for video games, 39 percent of the parents of pre-teens were concerned about the content of games they’d bought, as were 46 percent of parents of teens.

I could form a human bridge between me and Jesus, or Caesar, or Hero of Alexandria with only 26 people reaching out finger tip to finger tip across time.  Those 26 people could fit into one room.

Calculated this way 1,000, or even 2,000 years doesn’t seem so distant. To span 1,000 years we need only 13 lifespans. We can hold a list of 13 names connecting us to the year 1000 AD in our head, and many people in the past have done so.

Going in the opposite direction we can imagine only 13 lives (and perhaps fewer if longevity increases), linking us and the year 3000 AD. Between you and the year 3000 AD stand only 13 lifetimes. In terms of lifetimes — which are steadily increasing due to medical progress — 10 centuries is just next door.

Upwards of 85 percent of parents who receive a prenatal diagnosis of Down Syndrome elect to terminate the pregnancy, according to several studies in the peer-reviewed journal Prenatal Diagnosis. A 1999 British study in that journal found the termination rate to be between 91 and 93 percent. When I was a teenager in the 1980s, I remember seeing many people my age and younger who had the distinctive facial and behavioral characteristics of Down children. These days I rarely see a Down Syndrome child at all.

What is peculiar about Down Syndrome as a reason for termination is that, plainly put, you rarely meet a Down Syndrome “sufferer” who is notably unhappy. The condition has a range of manifestations, some more disabling than others, but many, many persons with Down Syndrome thrive as children and adults, even if they may not have the same range of capabilities as you or I do.

The fact that this syndrome has become a reason for termination is evidence of the terrible power of culture. A culturally neutral artifact (prenatal diagnosis of congenital diseases) combined with a culturally tragic artifact (elective abortion) begins to make it plausible that parents should avoid the challenges and risks of a Down pregnancy by ending it. The decreasing number of children born with the condition begins to make it more difficult to imagine that “normal” families can absorb the stresses of raising such a child, and undermines public support for public programs that support families who have made that decision. Which, over time, makes carrying a Down Syndrome baby to term ever more inconceivable, leading to increased rates of termination, leading to decreasing plausibility . . . until one day the burden of bringing a Down Syndrome child into the world is seen as so grave that less than 10 percent of parents take the risk.

But Sarah and Todd Palin have done it. I cannot think of any other public figures in my adult life, at least of the prominence they are about to enjoy or endure, who have made this decision. They will cause many, many families to reconsider the horizons of the possible. Their public example could very well lead to a cultural sea change—a dramatic shift in the “horizons of the possible.” That phrase from my book is no metaphor. Those horizons are so real that, for a future generation of children and their parents, they are quite literally a matter of life and death. For this reason, which utterly transcends politics and this year’s election, the sudden prominence of the Palins is, in the deepest sense, an extraordinary act of public service.