Desexing operations in animals are designed to not only stop reproduction as a population control, but also to prevent some of the unwanted secondary sex characteristics in adult animals, and to decrease sexual behavior in these animals. Castration of males has been carried out for centuries, and, originally, had more to do with increasing palatability of meat and decreasing aggressiveness in male farm animals than with population control. Spaying of females is rarely done in farm animals, since it is a relatively major surgery that does not offer the same advantages. In pets, spaying and neutering not only serve as the major means of reducing unwanted animals, but in making the animal more amenable to household living.
The same kind of operations have been carried out in people. Such surgery as excision of the testicles (in men), and removal of the ovaries and uterus (in women) is sometimes indicated for life-saving reasons, for example for treatment in some cases of cancer. In older women, who are no longer ovulating, removal of the ovaries is sometimes indicated for benign disease, and such surgery may be indicated in younger women for medical reasons besides malignancy. However, these operations in human beings have also been done for reasons that were later considered either to be outright war crimes that were part of a strategy to effect genocide, or performed for other reasons that are considered, today, to be unethical by a consensus of physicians and philosophers. These reasons have included attempts to control behavior, and to create a certain singing voice in men, called castrati.