"Human beings, as currently constituted, are good enough"

The first such threshold issue was nuclear weapons. The second one is climate change. And the next great one is this question of whether or not we are going to tinker with human genetics -- in particular, with the human germ line: with making genetic changes that we will pass on to future generations.

This technology is much riper than people understand. We've performed large-scale changes on every other mammal that you can name. And we have the capacity to begin to do it with people. There are teams of people now trying to clone human beings. Quite likely, we'll succeed. This is a fateful moment. If we go past it, then what our definition of a human being will change. We will think of ourselves as an endlessly improvable species, and that will have all kinds of sad effects.

For me, the saddest ones have less to do with all the practical dangers, or even with the very clear dangers to democracy, than with the even more basic questions of identity and meaning. It's extremely hard in the modern world to carve out an identity as it is, a thoroughgoing, full identity, because we have so little context in our lives. But now even our very individuality will be up for grabs. If you turn out to have been engineered by your parents to have a certain temperament or a certain kind of intelligence, you will spend your entire life unclear [about] what is you and what isn't, in a far deeper way than we have ever had to confront before.

So the point of this book, "Enough," is that we are reaching one of these really significant points in human history where we have to decide if we have enough power already and whether we can afford to bypass some. My contention is that we can, that human beings as currently constituted are good enough. In fact they're kind of wonderful in a lot of ways. And that it would be a grave mistake, for any reason, to begin to undermine that.

Happily, the technologies are such that you can use other, much less dangerous genetic technologies to deal with questions of human disease, to deal with cystic fibrosis or sickle cell anemia or the other sadnesses that are genetically transmitted. You don't need to do that kind of fundamental re-engineering of human embryos to accomplish those ends.

People don't realize that and tend to think of it all as a piece. Happily it isn't. One of the points of writing this book is to begin to explain those distinctions to people.

You've encountered scientists like James Watson. These scientists claim that it's precisely germ-line engineering which might save the human species from things like viral epidemics that might occur due to climate change.

Watson's biggest argument is that the epidemic he's most concerned about is the epidemic of human stupidity, and that's what we need to save people from by engineering their brains to make them work better.

James Watson has a very good brain for a certain kind of scientific inquiry. But I think there's very little indication in his other thinking that he sets the kind of standard for what we should aspire to in the human brain in general. I think we're OK without the upgrade.

When I interviewed Watson, he specifically mentioned germ-line engineering as a salvation from viral epidemics like AIDS.

The places where AIDS is endemic, across Africa, across Asia now, even across the poor parts of this country -- no one is seriously talking about doing germ-line engineering of tens of millions of embryos of poor people every year. That's a complete joke. I mean, you can't come up with 50 cents a year to provide them with bed nets to keep them from getting malaria.

We're not going to put IVF [in vitro fertilization] clinics in every corner of the developing world. Germ-line engineering is a technology aimed at the very rich to allow them to act out their whims and fantasies on their children.

So you would ban germ-line engineering? Is this one of the areas of progress that you would not want to be pursued, and instead we should enact laws forbidding its application to humans? If so, would you apply such a ban to other species as well?

My sense is that human genetic engineering is now a mature enough technology that we can begin to sense where the line should be. So-called somatic genetic engineering seems OK within appropriate bounds, treating people who already exist and who already have some problem, and in such a way that those changes aren't inheritable. That seems sensible. It can be misused. It needs to be governed carefully. Germ-line genetic engineering is on the other side of this "enough" point, it seems to me.

Next Page: "It's entirely possible to make the case that human beings are a huge problem and that we'd be better off with something else"

• View blog reactions