In the future, advances in genetic modification techniques will make it possible for us to change ourselves dramatically. Should we apply these techniques to ourselves? Should we apply them to our children? In answering these questions, we are hampered by the fact that the interests of an organism are determined by its design, at least in part. Having interests is a matter of possessing features, such as the ability to feel pain and pleasure, by which an organism can be concerned about itself. So choosing our design based on our interests seems circular. Still, we can take it for granted that we will wish to change our welfare apparatus, and that of our children, only in peripheral ways, and give preference to options that make our lifetime welfare level higher than other options. Several sorts of enhancement would benefit us. For example, if we can avoid senescence, we should extend our life span.