It's a basic rule of nature: where there is diversity, there is greater effectiveness. That's why no two people — not even twins — are genetically identical.In war, an army is more likely to win if it has a wide variety of weapons at its command: rifles, grenades, missiles, tanks, planes, etc. A diversified arsenal makes it possible for the troops to meet a considerably larger range of challenges in the course of combat.In art, a Picasso who can work in a broad spectrum of materials—paint and canvas, collage and metal—wins recognition as a genius.In medicine, the healer who can use a whole pharmacopeia of medicines, who has a greater number of choices available among a wide variety of therapies — medication, surgery, radiation, chemotherapy — is likely to produce the greater number of cures. By contrast, we recognize quackery when the practitioner claims he has the one remedy that will cure anything from flat feet to a brain tumor.