How can adaptive significance help explain vulnerability to disease?

In Darwinian medicine, adaptive significance helps explain why the human body remains vulnerable to disease by highlighting that natural selection shapes traits for reproductive success rather than for optimal health or longevity.1

Vulnerability often arises because traits that provide a survival or reproductive advantage can simultaneously carry inherent costs or trade-offs. For example, bones could be thicker to prevent injury, but the resulting increase in weight would hinder mobility and speed. Similarly, mutations that enhance reproductive fitness may spread through a population even if they negatively impact long-term health.1

Furthermore, many perceived "diseases"—such as fever, pain, and anxiety—are actually protective, adaptive responses. These mechanisms are often "over-expressed" due to the smoke-detector principle: because the cost of a false alarm is low compared to the catastrophic cost of failing to respond to a genuine threat, natural selection favors sensitive, defensive responses that may appear excessive or uncomfortable to the individual.1