Why do evolved bodily defenses sometimes create false alarms?

In the field of Darwinian medicine, bodily defenses such as pain, fever, and anxiety are considered protective responses shaped by natural selection rather than diseases themselves.1

These defenses sometimes create false alarms due to what is known as the "smoke-detector principle." Much like a smoke detector that is intentionally calibrated to be highly sensitive—triggering an alarm even when someone is simply making toast—the human body’s defensive mechanisms are designed to prioritize survival.1

The evolutionary logic is that the cost of a false alarm is typically minor, whereas the cost of failing to express a necessary defense during a genuine threat (such as a fire or an infection) could be catastrophic. Consequently, because the cost of these defenses is relatively low compared to the potential danger of not being alerted when a threat is present, natural selection has favored mechanisms that frequently produce excessive or unnecessary responses.1