This paper critically examines the biology of species identity and the morality of crossing species boundaries in the context of emerging research that involves combining human and nonhuman animals at the genetic or cellular level. We begin with the notion of species identity, particularly focusing on the ostensible fixity of species boundaries, and we explore the general biological and philosophical problem of defining species. Against this backdrop, we survey and criticize earlier attempts to forbid crossing species boundaries in the creation (...) of novel beings. We do not attempt to establish the immorality of crossing species boundaries, but we conclude with some thoughts about such crossings, alluding to the notion of moral confusion regarding social and ethical obligations to novel interspecies beings. (shrink)

: The transplantation of adult human neural stem cells into prenatal non-humans offers an avenue for studying human neural cell development without direct use of human embryos. However, such experiments raise significant ethical concerns about mixing human and nonhuman materials in ways that could result in the development of human-nonhuman chimeras. This paper examines four arguments against such research, the moral taboo, species integrity, "unnaturalness," and human dignity arguments, and finds the last plausible. It argues that the transfer of human (...) brain or retinal stem cells to nonhuman embryos would not result in the development of human-nonhuman chimeras that denigrate human dignity, provided such stem cells are dissociated. The article provides guidelines that set ethical boundaries for conducting such research that are consonant with the requirements of human dignity. (shrink)

Articulating the public's widespread unease about animal biotechnology has not been easy, and the first attempts have not been able to provide an effective tool for navigating the moral permissibility of this research. Because these moral intuitions have been difficult to cash out, they have been belittled as representing nothing more than fear or confusion. But there are sound philosophical reasons supporting the public's opposition to animal biotechnology and these arguments justify a default position of resistance I call the Presumption (...) of Restraint . The Presumption of Restraint constitutes a justificatory process that sets out the criteria for permitting or rejecting individual biotechnology projects. This Presumption of Restraint can be overridden by compelling arguments that speak to a project's moral and scientific merit. This strategy creates a middle-of-the-road stance that can embrace particular projects, while rejecting others. The Presumption of Restraint can also serve as a model for assessing moral permissibility in other areas of technological innovation. (shrink)