LAUSR

By modifying environmental conditions, human activities are generating novel selection pressures, which pose challenges to wildlife (1–3). When faced with novel selection pressures, organismal populations can respond to this through evolutionary adaptation, modifying their phenotype through plastic changes, or evading these new pressures by migrating to more beneficial environments (4). Otherwise, they will face loss of fitness and eventually, even extirpation. Although alteration of natural environments by humans has been long recognized as a potential source of novel and strong selection pressures, demonstrating human-induced evolution has proven to be challenging (4–6). In PNAS, Jensen et al. (7) provide intriguing evidence for rapid human-induced evolution in body size of Atlantic salmon (Salmo salar) within just 25 y. Atlantic salmon (Fig. 1A) are mighty creatures; individual fish from large rivers can occasionally grow to weigh over 37 kg (80 pounds). However, the average size of salmon shows great variance both within and among different river systems. Much of this variation can be attributed to variation in the time the salmon spend at sea—the later they mature and run into rivers to breed, the larger they