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Fitness and adaptive landscapes have theoretical limitations, but they have played a valuable role in integrating population genetics and macroevolution. Sewall Wright introduced fitness landscapes in 1931 to describe the relationship between genotypes and fitness, and George G. Simpson modified and popularized the concept of landscapes in evolutionary biology in 1944 as adaptive landscapes to illustrate the evolutionary response of fossil lineages to natural selection. Patterns of sediment and fossil accumulation impose practical limitations on the use of adaptive landscapes to analyze fossil data. Phenotypic evolution can occur too rapidly to resolve in the stratigraphic record, hindering observation of movement of lineages upward on an adaptive peak. Use of the null hypothesis of a random phenotypic walk through time (i.e., genetic drift) to test for adaptation in the trajectory of change in fossil lineages has consistently led to rejection of adaptation, but recent methods, including a maximum likelihood procedure for individual lineages and simultaneous analysis of multiple species and traits, indicate that fossil lineages have ascended adaptive peaks and remained at their summits as they shift position through time. Recognition of the limits to temporal resolution in fossil lineages provide guidance for the selection of fossil lineages to study, and development of new statistical tools have enhanced the value of adaptive landscapes to analyze the fossil record.

This chapter reviews the evidence for the late fifth and early fourth millennia cal bc in the Thames Valley. Throughout the period under study, there are strong strands of continuity. The utilization of tree-throw holes, the small-scale digging of pits, the creation and abandonment of occupation spreads, and the accumulation of occupation material into middens are common to both periods. However, in the fourth millennium cal bc, communities began to alter their landscape through increasingly substantial building projects: first houses and then monuments. There was more visible treatment of the dead and deposition of human remains. Clearings became more extensive, perhaps largely for pasture, and small cultivation plots were created. Cereals, domesticated animals, new flint tools, and Carinated Bowls are found on all sites from the beginning of the fourth millennium cal bc. It is tempting to try to rationalize this evidence into explanations of either indigenous populations adopting a new way of life, using the evidence of continuity (which is strong); or incomers, pioneer farmers bringing their own material culture and different social practices, as witnessed by the new elements in the archaeological record. But perhaps we should not be thinking in terms of either/or, but rather both.