The thrust of this book is that pressures and stresses on peripheral populations in areas of population growth have driven the changes that have marked human biological and cultural evolution. It has been the stressed populations that have been the most innovative (e.g. Fitzhugh, 2001). Hominids have responded to the increasing instability with risk reduction responses that fit under the umbrella of increasing the spatio-temporal scale of operation. Correlates of increase in scale have included, as we saw in Chapter 5, an increase in dispersal ability, home range size, group size, neocortex size, the complexity of social behaviour, symbolism, efficient and mobile tool kits, and gracile morphology. Since global climate and environments have become increasingly unstable over the last two million years those marginal populations that adapted to local stresses in these ways were able to turn disadvantage into advantage each time conditions deteriorated or became less stable. These adaptations would have evolved in peripheral populations that perceived marginal landscapes as spatially heterogeneous and therefore spatially risky. These adaptations to exploiting patchy landscapes then became advantageous in situations of increasing temporal heterogeneity, that is in situations that were perceived as temporally risky. We can therefore understand these adaptations as evolving through a normal process of natural selection and we do not need to invoke alternative mechanisms, such as variability selection (Potts, 1996a, b, 1998), to explain the observed patterns and trends. Most of these adaptations would have been behavioural.