Adaptive Markets Hypothesis

The Adaptive Markets Hypothesis (AMH), proposed by economist Andrew Lo, holds that market efficiency is not a static property of financial systems but an adaptive one — a function of the ecological conditions in which market participants operate. When environments are stable and predictable, the efficient markets hypothesis approximately holds: competition drives agents toward optimal behavior and prices toward fundamental value. When environments shift — through technological disruption, regulatory change, or macroeconomic shock — the same competitive dynamics produce maladaptive behavior: herding, panic, and behavioral bias dominate until a new equilibrium emerges.

The AMH treats financial markets as complex adaptive systems in which the strategies of participants, not just their trades, evolve under selection pressure. Strategies that worked in one regime become obsolete in the next; the survivors are not necessarily the most rational but the most robust to regime change. This evolutionary framing dissolves the false dichotomy between rationality and irrationality: both are context-dependent outcomes of the same adaptive process, just as a polar bear is superbly adapted to the Arctic and helpless in the tropics.