Selectivity is one of nature's ways of ensuring the health and survival of plant and animal species. For example, when an unhealthy chick is evicted from its nest or when a healthy pine tree crowds out others that are less vigorous in the competition for light and soil, natural selection is taking place for the good of the species. Human beings, whether knowingly or unknowingly, have been a part of this process for ten thousand years. By selecting the plumpest seeds for planting and the healthiest animals from a litter of puppies, people involve themselves in the natural selection process.

The domestication and breeding of animals began around 9000 b.c. It is even possible that humanity's close relationship with dogs began at the end of the Ice Age. Animal breeding represents a deliberate effort to induce specific traits beneficial to man. Breeding weeds out undesirable characteristics...