Why can anxiety be an evolved protective response?

In the field of Darwinian medicine, anxiety is understood not as a disease, but as an evolved, protective response shaped by natural selection.1

As an adaptive mechanism, anxiety serves to signal potentially harmful internal or external changes, enabling individuals to avoid danger or cope with stress. From an evolutionary perspective, the utility of such defenses is often explained by the "smoke-detector principle." Much like a sensitive smoke detector that may trigger a false alarm when making toast, the cost of a false alarm is minor compared to the catastrophic cost of failing to be alerted to a real fire.21

Consequently, because the cost of expressing a defense is generally low compared to the risk of not expressing it when a threat is present, natural selection has favored mechanisms that frequently produce "false alarms" or apparently excessive responses. While these responses are protective in nature, they can become problematic when they occur without clear cause or in an exaggerated manner, potentially leading to anxiety disorders.12