As hard as they are to rationally reconstruct, it is important to listen to concerns that some form of biomedicine violates human nature, even in public discussions of policy within a pluralistic society. Whether the concern is the distortion of some constant of the human condition, like senescence, or a “species altering” threat to our collective gene pool, or the corruption of practices designed to celebrate the inherited human traits we value most, these appeals all signal that the intervention in question has deep implications for who we want to be, given who we have been. However, respecting what we have (or have not) inherited from our parents does not in itself fulfill the need to decide which promises we would like to make to our children. Invocations of particular vulnerabilities, loyalties, or forms of sociality from the past can provide fodder for arguing over the positive visions of human nature that should guide those promises. But in communities that accept the possibility of a pluralism of promises, such invocations should also trigger another policy-making response: the need for policy-makers to protect the interests of those excluded from their visions, even while we discuss their merits. The natural human gene pool has no top, bottom, edges or direction: it cannot be “used up”, “diverted”, “purified” or “polluted”. The reservoir of human mutual respect, good will and tolerance for difference, however, seems perennially in danger of running dry. That is our human nature’s truly fragile heritage that we should seek to preserve—and some say even enhance—in monitoring biomedical research on behalf of the future.