Is nanotechnology-based human enhancement morally permissible? One reason to question such enhancement stems from a concern for preserving our species. It is harder than one might think, however, to explain what could be wrong with altering our own species. One possibility is to turn to the environmental ethics literature. Perhaps some of the arguments for preserving other species can be applied against nanotechnology-based human enhancements that alter human nature. This paper critically examines the case for using two of the strongest (...) arguments in the environmental ethics literature to show that nanotechnology-based human enhancements are impermissible: 1) Our species, like many other naturally occurring species, has aesthetic value. So, nanotechnology-based human enhancements that alter our species should be prohibited. 2) Our species plays valuable ecological roles. Nanotechnology-based human enhancements that alter our species are likely to interfere with our species playing our ecologically valuable roles. So, such enhancements should be prohibited. Neither argument, ultimately, proves conclusive. The paper concludes, however, that considerations underlying both arguments may show us that some nanotechnology-based human enhancements are impermissible. (shrink)