Answer to Question 1
Theories of aging can be examined from two perspectives: (1) programmed aging theories and (2) wear-and-tear theories. Programmed aging theories include Hayflick's Theory of Limited Cell Replication, and the Molecular Clock Theory. Wear-and-Tear Theories of Aging include the Free-Radical or Oxidative Stress Theory, and the Rate of Living Theory.
Studies have shown that caloric restriction, especially in midlife, results in longer life spans. One mechanism might be that it leads to changes in cell signaling pathways that induce metabolic reprogramming and subsequent life extension.
Answer to Question 2
a