Dispersal is a ubiquitous trait in living organisms. Evolutionary theory postulates that the loss or death of propagules during dispersal episodes (cost of dispersal) should select against dispersal. The cost of dispersal is expected to be a strong selective force in fragmented habitats. We analyzed patchy populations of the weed Crepis sancta occupying small patches on sidewalks, around trees planted within the city of Montpellier (South of France), to investigate the recent evolutionary consequences of the cost of dispersal. C. sancta produces both dispersing and nondispersing seeds. First, we showed that, in urban patches, dispersing seeds have a 55% lower chance of settling in their patch compared with nondispersing seeds and, thus, fall on a concrete matrix unsuitable for germination. Second, we showed that the proportion of nondispersing seeds in urban patches measured in a common environment is significantly higher than in surrounding, unfragmented populations. Third, by using a quantitative genetic model, we estimated that the pattern is consistent with short-term evolution that occurs over Ϸ5-12 generations of selection, which is generated by a high cost of dispersal in urban populations. This study shows that a high cost of dispersal after recent fragmentation causes rapid evolution toward lower dispersal.fragmentation ͉ short-term evolution ͉ human-altered habitat D ispersal has evolved in almost all living organisms and is thus considered as a central life-history trait (1, 2). The evolution of dispersal is usually understood as the result of a cost-benefit process. On the one hand, three main factors selecting for dispersal have been identified (3): reduction of the competition among kin (4, 5); the temporal heterogeneity of the environment, such as local population extinction (6, 7); and last, the avoidance of inbreeding depression when mating occurs between related individuals (8). However, various costs of dispersal have been postulated in theoretical models. For instance, dispersal structures can be costly for organisms [e.g., fleshy fruits dispersed by animals (9)]. More generally, dispersing organisms may pay a high cost of dispersal because they may get lost during the displacement. This phenomenon is encapsulated under the term ''cost of dispersal.'' Various theoretical models have been studied, including various selective factors (3). These theoretical models conclude that increasing the cost of dispersal selects for lower dispersal. Although this cost may appear as obvious in natural populations, the strength of this selection pressure on dispersal traits is almost unknown in the wild because of the difficulties of measuring it in natural systems. When dispersal is passive (wind or water transport) and habitat choice is random, the probability of settling in a suitable site is positively dependent on the frequency of suitable sites in the landscape. Many empirical studies have reported a reduction in dispersal structures in organisms that live on islands, such as plants (10) or insects (ho...