In his 2006 State of the Union speech, President George W. Bush asked the U. S. Congress to prohibit the "most egregious abuses of medical research," such as the "creation of animal--human hybrids." The president's message echoed that of a 2004 report by the President's Council on Bioethics, which recommended that hybrid human--animal embryos be banned by Congress.

Discussions of early interspecies research, in which cells or DNA are interchanged between humans and nonhumans at early stages of development, can often devolve into sweeping statements, colorful imagery, and confusing policy. Although today's policy advisory groups are becoming more informed, debate is still limited by the interchangeable use of terms such as chimeras and hybrids, a tendency to treat all forms of interspecies alike, the failure to distinguish between laboratory research and procreation, and not enough serious policy justification. Andrea Bonnicksen seeks to understand reasons behind support of and disdain for interspecies research in such areas as chimerism, hybridization, interspecies nuclear transfer, cross-species embryo transfer, and transgenics. She highlights two claims critics make against early interspecies studies: that the research will violate human dignity and that it can lead to procreation. Are these claims sufficient to justify restrictive policy?

Bonnicksen carefully illustrates the challenges of making policy for sensitive and often sensationalized research -- research that touches deep-seated values and that probes the boundary between human and nonhuman animals.

At issue in this book are studies that combine genes, gametes, embryos, or embryonic stem (ES) cells from human and nonhuman species at the earliest stages of development. What is here called early interspecies research (ISR) involves the shared presence of human and/ or animal embryos and es cells in a potentially inheritable way. the prospect of such studies has been flagged, whether justifiably or not, by a number of observers and policy makers as problematic.

One example of early isr is the injection of human es cells into a mouse blastocyst (four- to six-day embryo of approximately three hundred cells) in order to understand how human es cells function over time in a living system. As the fetal mouse develops, the human cells differentiate and integrate. the ultimate goal is to understand the properties of es cells better in order to develop cell-based therapies for humans. the recipient mice, studied before or after birth, would be chimeras, with some human cells existing side by side with mouse cells.

A second example is the substitution of animal eggs for human eggs in investigations geared to developing cell therapies for humans. in theory, if the nucleus from a patient’s somatic cell is introduced to an enucleated egg, the egg can be stimulated to cleave and will yield an inner cell mass from which es cells can be derived after about five days. These es cells, which are capable of differentiating to virtually any type of body cell, can be coaxed to differentiate and used for cell replacement therapies. the goal is to derive es cells that have the same genome as the patient who provided the nucleus. Many eggs would be needed in these preliminary studies, so investigators have proposed using animal eggs, which . . .