How fast is evolution? In this dissertation I document a profound change that occurred around the middle of the 20th century in the way that ecologists conceptualized the temporal and spatial scales of adaptive evolution, through the lens of British plant ecologist Anthony David Bradshaw (1926–2008). In the early 1960s, one prominent ecologist distinguished what he called “ecological time”—around ten generations—from “evolutionary time”— around half of a million years. For most ecologists working in the first half of the 20th century, evolution by natural selection was indeed a slow and plodding process, tangible in its products but not in its processes, and inconsequential for explaining most ecological phenomena. During the 1960s, however, many ecologists began to see evolution as potentially rapid and observable. Natural selection moved from the distant past—a remote explanans for both extant biological diversity and paleontological phenomena—to a measurable, quantifiable mechanism molding populations in real time.

The idea that adaptive evolution could be rapid and highly localized was a significant enabling condition for the emergence of ecological genetics in the second half of the 20th century. Most of what historians know about that conceptual shift and the rise of ecological genetics centers on the work of Oxford zoologist E. B. Ford and his students on polymorphism in Lepidotera, especially industrial melanism in Biston betularia. I argue that ecological genetics in Britain was not the brainchild of an infamous patriarch (Ford), but rather the outgrowth of a long tradition of pastureland research at plant breeding stations in Scotland and Wales, part of a discipline known as “genecology” or “experimental taxonomy.” Bradshaw’s investigative activities between 1948 and 1968 were an outgrowth of the specific brand of plant genecology practiced at the Welsh and Scottish Plant Breeding stations. Bradshaw generated evidence that plant populations with negligible reproductive isolation—separated by just a few meters—could diverge and adapt to contrasting environmental conditions in just a few generations. In Bradshaw’s research one can observe the crystallization of a new concept of rapid adaptive evolution, and the methodological and conceptual transformation of genecology into ecological genetics.