A Reflection on Theories of Aging

Aging remains one of the most complex phenomena in biology, giving rise to a diverse range of theoretical frameworks aimed at elucidating its mechanisms. These theories often overlap, exhibiting both consistencies and contradictions, making it challenging to systematically categorize them. In this review, we revisit prominent aging theories from multiple perspectives. First, from the classical viewpoints of “wear-and-tear” and “programmed” aging, we introduce several foundational theories, including the oxidative damage family theories and information theory. We then examine these theories from an evolutionary perspective, which leads to the antagonistic pleiotropy (AP) theory and the hyperfunction theory. Following the mechanistic discussion, we consider several inclusive theories, including the “np” theory. Analogies are used throughout, and each section concludes with a philosophical reflection on the essence of aging. All discussions are centered on a fundamental question: “Is lifespan constrained by what nature does not pursue, or by what it fundamentally cannot achieve?” At least according to the “np” theory, an ultimate restriction stems from the information entropy. Finally, we highlight emerging rejuvenation strategies, which provide alternative lens to view aging theories. This review aims to inspire readers to think critically about current theories and to explore novel conceptual frameworks in the biology of aging.