maladaptations

Maladaptation is a term used in evolutionary biology to describe a trait, behavior, or set of traits that reduces an organism's fitness in its current environment. It can arise when a feature was advantageous under historical conditions but becomes harmful as environments, ecological interactions, or selective pressures change. Maladaptations can also persist because of genetic constraints, trade-offs, pleiotropy, or time lags between environmental shifts and genetic adaptation. In this sense, maladaptation is not simply a lack of adaptation; it is a mismatch between an organism's traits and its present circumstances.

Causes include rapid environmental change, such as climate shifts or human-induced habitat alteration, which outpace evolution. Small population size can allow maladaptive variants to persist by drift. Trade-offs mean improving one function reduces another, potentially yielding net fitness costs. Pleiotropy can couple multiple traits so that selection on one aspect harms others. Gene flow between populations can prevent local adaptation, maintaining maladaptive traits in some contexts.

Common illustrations include sexually selected ornamentation that increases mating success but elevates predation risk or energy expenditure, as in the peacock's tail. In humans, mismatches between evolved physiology and modern lifestyle—such as energy-saving mechanisms that favor fat storage—can contribute to obesity and metabolic disorders. Similarly, traits optimized for past climates or resource regimes can become less effective under new conditions, producing maladaptive performance or reduced survival and reproduction.

Maladaptation is a context-dependent concept; a trait can be maladaptive in one environment but neutral or beneficial in another. It remains a focus for understanding how populations navigate changing ecosystems and anthropogenic pressures.