Many philosophers invoke the "wisdom of nature" in arguing for varying degrees of caution in the development and use of genetic enhancement technologies. Because they view natural selection as akin to a master engineer that creates functionally and morally optimal design, these authors tend to regard genetic intervention with suspicion. In Part II, we examine and ultimately reject the evolutionary assumptions that underlie the master engineer analogy (MEA). By highlighting the constraints on ordinary unassisted evolution, we show how intentional genetic modification can overcome many of the natural impediments to the human good. Our contention is that genetic engineering offers a solution that is more eff icient, reliable, versatile, and morally palatable than the lumbering juggernaut of Darwinian evolution. In Part III, we evaluate a recent attempt to ground precautionary enhancement heuristics in adaptive etiology. Our problem with this approach is two-fold: first, it is based on the same "strong adaptationist" interpretation of evolution that motivates the flawed MEA, and second, the etiological concept of function on which it relies provides indirect and potentially misleading information about the likely consequences of genetic intervention. We offer instead enhancement criteria based on causal relationships in ontogeny. We conclude that rather than grounding a presumption against deliberate genetic modification, the causal structure of the living world gives us good moral reason to pursue it.