"Teleofunctions and Oncomice"

The view that organisms deserve moral respect because they have their own purposes is often grounded in a specification of the biological functions that the organism has. One way to identify such functions is to determine the etiology of some behavior based on the evolution of the structures enabling it. This view suffers from some unacceptable problems, including that some organisms with profound defects will by definition have a welfare interest in their defects. For example, the patented oncomice, intentionally engineered and bred for a genetic defect that leads to extremely high incidence of cancer, would have a welfare interest in the development of tumors. The systems-based theory of biological functions, which refers not to the evolution of structures but rather their role in the organism, escapes these problems, and shows how a theory of an organism's welfare interest in its purposes can be grounded in a sound naturalistic approach. This approach also has some fruitful corollaries, including an elegant theory of why species may require special moral regard.
Environmental Ethics, Summer Vol. 26: 171-188.