Chimeras are transgenic organisms that contain two or more different populations from genetically distinct cells that originated in different zygotes. Chimeras can involve the mixing of species from a human and a rat to a chicken and an elephant. According to Nancy L. Jones, fellow at the Center for Bioethics and Human Dignity, transgenic mice containing human genes have existed for over twenty years. While chimeras have the potential of medical therapy, the process raises questions about issues such as: creation of new life forms and crossing species boundaries, the long-term effects on human health and the environment; the blending of plant, nonhuman animal and human DNA, the unintended personal, social, and cultural consequences.