 However, Naked mole rats have a high telomerase activity; they live long, and never get cancer; they are, therefore an exception to this hypothesis.Theories, such as Weismann's "programmed death" theory, suggest that deterioration and death due to ageing are a purposeful result of an organism's evolved design, and are referred to as theories of programmed ageing or adaptive ageing.The programmed maintenance theory based on evolvability suggests that the repair mechanisms are controlled by a common control mechanism capable of sensing conditions, such as caloric restriction, and may be responsible for lifespan in particular species.