Generation time is not a universal constraint on adaptive evolution

Conventional wisdom suggests that adaptive evolution proceeds more slowly in long-lived organisms than in short-lived ones due to longer generation times. As a result, long-lived organisms are often viewed as less capable of responding to rapid environmental change. However, empirical evidence challenges this view. Using mathematical models and demographic data from 322 wild animal populations, we show that long generation times slow adaptive evolution only under limited conditions, notably when selection acts on fecundity. When selection targets early survival, intermediate and long generation times can instead accelerate adaptive evolution. Remarkably, short-lived species tend to occupy demographic regimes in which fecundity is the dominant fitness component, whereas long-lived species occupy regimes in which early survival dominates. Therefore, both short- and long-lived species can potentially adapt rapidly, calling into question the widespread use of generation time as a general predictor of adaptive capacity to current environmental change.