Exercised: Why Something We Never Evolved to Do Is Healthy and Rewarding

by Daniel E. Lieberman

in understanding depression and anxiety disorders, but as articulated by Randolph Nesse and others, an evolutionary perspective that considers these diseases as adaptations gone awry may help explain why we are so vulnerable and why they are so varied.124 It is obviously adaptive for fear to lead us to avoid threats like poisonous snakes or being attacked by strangers. In anxiety disorder, however, these normal anxieties become irrational and uncontrolled. Likewise, it may sometimes be adaptive to be discouraged and unmotivated, hence disinclined to engage in behaviors unlikely to be successful like fighting someone who might kill us or wooing a lover who spurns us. In depression disorder, however, these low moods become directed persistently at ourselves, not the outside world. Just how and why these sorts of adaptive mechanisms turn pathological is poorly understood. As with all diseases, they involve interactions between genes and many complex environmental factors. But an evolutionary perspective prompts us to scrutinize the crucial role of the environment: Could these too be mismatch diseases? Are we vulnerable because we now face environmental factors, requiring less physical activity, that we never evolved to handle?