When Bill McKibben looks into the future, he sees a world where people may live forever, where parents could choose to have a child with the smarts of a Nobel Prize–winner, the body of an Olympic athlete, and the looks of a supermodel. And he
doesn’t like it one bit.

In his recent book, Enough: Staying Human in an Engineered Age, the best-selling environmental author suggests that we are on the cusp of changing—perhaps irrevocably—what it means to be human. With our genetic material recently mapped, new applications of this knowledge are constantly being developed. But while some advances seem beneficial and benign, such as infertility treatments, better prenatal tests, and customized pharmaceuticals, others, McKibben argues, are too dangerous to pursue.

A mild, soft-spoken man, McKibben draws a firm line between somatic gene therapy—inserting healthy genes into a sick person’s cells to help them heal—and so-called germline, or inheritable, genetic modification. The latter is the technique that could produce "designer babies" by changing an embryo’s genes to make a child smarter, prettier, or stronger—traits that would then pass on to offspring.

In Enough, McKibben makes a passionate case that inheritable alteration would rob future generations of the chance to determine their own identities. A parent himself, McKibben admits that "we already ‘engineer’ our offspring in some sense: We do our best, and often our worst, to steer them in particular directions . . . but our gravity is usually weak enough that kids can break out of it if and when they need to." Children "programmed" to run marathons, paint masterpieces, or win scientific awards would have no such opportunity.

Critics like McKibben see in this possibility troubling similarities to early eugenicists’ attempts to "improve" the gene pool; they also see a threat to our common heritage. Like our air, water, and wildlands, they say, our genes belong to all of us. But with some 20,000 patents already issued in the United States for genes and related material (and another 20,000 under consideration), our genetic future is quickly falling into corporate hands. Without stringent safeguards, our genes may become property of the highest bidder, further severing our links with nature and our sense of ourselves as part of a larger ecosystem. If science can make everything "perfect," after all, there would be little incentive to be good stewards, of our own bodies, or of the rest of the world.

Sierra: Is human genetic engineering an environmental issue?

Bill McKibben: One of the things I mean when I say that I’m an environmentalist is that I have an innate preference for the world as we were born into it, for the flora and fauna that are here now. Respecting that means not trying to change it in major ways. Likewise, I believe that human beings are not in need of radical overhaul, improvement, or augmentation. As we are now constituted, we are plenty good enough.

Sierra: You’ve said that this is one of the "threshold moments" where we really have to consider whether we’re willing to just stop where we are. What were the others?

McKibben: In our time on Earth, this is the fourth such moment. The first was the invention of nuclear weapons, and the sudden realization that we could obliterate everything in the blink of an eye. Another is climate change, and the realization that one species’ habits are courting changes as large as those caused by the last asteroid that hit the earth.

But the third and best example, I think, was the population-boom debate back in the 1970s. Over the last 30 years, human beings have realized it’s necessary to bring our numbers under control, so educated and empowered women have seen their average fertility drop from 4.5 children to 2.7. That’s a pretty remarkable accomplishment. It may have come a little late, but it’s a far sight better than just multiplying our numbers endlessly and seeing what happens.

Sierra: Often developments hailed as "progress" end up having unforeseen consequences. What can we learn from those experiences?

McKibben: In general, I think we should count ourselves the lucky inheritors of 500 years of scientific progress. We live long, comfortable, easy lives in the West. The question is, Should we keep pressing endlessly forward or decide to rule out certain quantum leaps?

It’s extremely hard to imagine what the planet would actually be like if it were five degrees warmer, or what it would feel like to be an engineered product instead of a child. Part of my work is to try to foresee enough of the consequences that we avoid making this huge leap.

Sierra: Throughout your book you emphasize the idea that here in the West we have enough. How do these new technologies apply to the rest of the world?

McKibben: They really don’t. People talk about how genetic therapies could treat this or that disease in developing countries, but it’s a joke. We can’t come up with enough money for bed nets to prevent people from getting malaria from mosquitoes; we’re not going to go build in-vitro fertilization clinics along the length and breadth of Africa. And in this country, where we can’t bring ourselves to provide health care to 40 million people, we’re not going to extend genetic modifications to the poor.

Sierra: So why should people who can’t afford it, or don’t want to, care if a few rich people do this?

McKibben: If human genetic engineering becomes widespread in any given society, the pressure will be enormous on people who can’t afford it to do it, because otherwise their children will be at a disadvantage. The only people who will get to make a clear, clean choice about it will be the first ones. After that, the choices become strategic instead of moral.

Not even the proponents think any differently. Geneticist Lee Silver has written about how the world is going to be divided into the "GenRich" and the "Naturals." We would be rewriting into our biology the differences in wealth and power that bedevil our society today. In Silver’s not-so-distant future, genetically enhanced people and natural people would be unable even to interbreed. That’s not a world I want to live in.

Sierra: Could all this really happen soon?

McKibben: It may be a while. We don’t yet know what the obstacles will be. But in my 1989 book, The End of Nature, I wrote a few pages about the then-infant science of agricultural biotechnology. A decade later, half the soybean fields and one-third of the cornfields in this country were planted with genetically modified organisms. Things can happen very quickly once technology gets up and rolling.

Sierra: What can environmentalists do to make sure these kinds of changes don’t take place without open debate?

McKibben: One of the things that I’m afraid I and other environmentalists have to answer for is the notion that human beings are some kind of malignancy. If that were true, maybe it would be a good idea to alter us or engineer us. Instead, we need to show some of the same generosity toward the human animal that we’ve shown toward a lot of other animals, some of the same affection. For all the obvious troubles that we’ve blundered into, we’re also pretty remarkable.

Sierra: Is there anything environmentally good about these new technologies, such as, say, cloning almost-extinct species to save them?

McKibben: We like easy technological fixes. But if we’re serious about dealing with the threat to biodiversity on Earth, for example, then we have to get down to all the dull, dreary work of preserving habitat, of figuring out how people are going to make their living in roughly the same places nature is making its living without either one overwhelming the other. That’s hard work; it requires changing our habits, and yet it offers something real in the end.