The damage caused by biological invasions has traditionally been thought to result from alien species taking advantage of ecological differences between the native and introduced ranges. In contrast, the role of evolutionary forces has received relatively little attention. Our results show that evolutionary change in Silene latifolia, a North American weed that was introduced from Europe about 200 years ago, can help explain the plant's successful North American invasion. By growing plants from seed collected in 40 populations from Europe and North America under common garden greenhouse and field conditions, we found significant genetic differences in life history, reproductive, and defensive characters. In general, morphological traits and competitive ability remained unchanged, while North American plants germinated earlier, grew faster, produced more flowers, had greater survival, and invested less into defensive traits (trichomes, fruit capsule) than their European conspecifics. We suggest that as S. latifolia escaped a suite of specialist enemies, natural selection favored individuals that invest more in growth and reproduction and less in defense.