1 The Last Human God and Nature first made us what we are, and then out of our own created genius we make ourselves what we want to be . Let the sky and God be our limit and Eternity our measurement. -Marcus Garvey (18871940) We know that Homo sapiens is not the final word in primate evolution, but few have yet grasped that we are on the cusp of profound biological change, poised to transcend our current form and character on a journey to destinations of new imagination. At first glance, the very notion that we might become more than "human" seems preposterous. After all, we are still biologically identical in virtually every respect to our cave-dwelling ancestors. But this lack of change is deceptive. Never before have we had the power to manipulate human genetics to alter our biology in meaningful, predictable ways. Bioethicists and scientists alike worry about the consequences of coming genetic technologies, but few have thought through the larger implications of the wave of new developments arriving in reproductive biology.
Today in vitro fertilization is responsible for fewer than 1 percent of births in the United States; embryo selection numbers only in the hundreds of cases; cloning and human genetic modification still lie ahead. But give these emerging technologies a decade and they will be the cutting edge of human biological change. These developments will write a new page in the history of life, allowing us to seize control of our evolutionary future. Our coming ability to choose our children's genes will have immense social impact and raise difficult ethical dilemmas. Biological enhancement will lead us into unexplored realms, eventually challenging our basic ideas about what it means to be human. Some imagine we will see the perils, come to our senses, and turn away from such possibilities. But when we imagine Prometheus stealing fire from the gods, we are not incredulous or shocked by his act. It is too characteristically human.
To forgo the powerful technologies that genomics and molecular biology are bringing would be as out of character for humanity as it would be to use them without concern for the dangers they pose. We will do neither. The question is no longer whether we will manipulate embryos, but when, where, and how. We have already felt the impact of previous advances in reproductive technology. Without the broad access to birth control that we take so for granted, the populations of Italy, Japan, and Germany would not be shrinking; birth rates in the developing world would not be falling. These are major shifts, yet unlike the public response to today's high-tech developments, no impassioned voices protest birth control as an immense and dangerous experiment with our genetic future. Those opposing family planning seem more worried about the immorality of recreational sex than about human evolution. In this book, we will examine the emerging reproductive technologies for selecting and altering human embryos.
These developments, culminating in germline engineering - the manipulation of the genetics of egg or sperm (our "germinal" cells) to modify future generations - will have large consequences. Already, procedures that influence the germline are routine in labs working on fruit flies and mice, and researchers have done early procedures on nonhuman primates. Direct human germline manipulations may still be a decade or two away, but methods of choosing specific genes in an embryo are in use today to prevent disease, and sophisticated methods for making broader choices are arriving every year, bringing with them a taste of the ethical and social questions that will accompany comprehensive germline.