Evolutionary Rescue

Evolutionary rescue is the recovery of a population from demographic decline through natural selection acting on pre-existing or newly introduced genetic variation, rather than through direct demographic intervention such as habitat restoration or predator control. The population saves itself by evolving faster than it goes extinct — a race between adaptation and annihilation that depends on the supply of beneficial mutations, the strength of selection, and the generation time of the organism.

Evolutionary rescue is broader than genetic rescue: the latter restores variation through migration, while the former can also occur through de novo mutation within the declining population. But the two processes often work in tandem. A population that receives immigrants gains not only immediate heterotic fitness but also new raw material for selection to act upon. The rescue of the Florida panther, for instance, combined both mechanisms: hybrid vigor improved immediate fitness, while the expanded gene pool enabled subsequent adaptive evolution.

The concept has gained urgency with climate change, as populations face novel thermal, hydrological, and biotic regimes faster than their historical rates of adaptation. Whether evolutionary rescue is possible under rapid anthropogenic change remains one of the most consequential open questions in conservation biology. The optimistic view holds that many populations harbor sufficient cryptic variation. The pessimistic view notes that generation times are long, mutation rates are low, and the rate of environmental change is unprecedented.