Causes and Consequences in Human Evolution

Abstract

Explanations for both the origins of humans and the pattern of human evolution have been diverse, imaginative and often erroneous. The problems associated with both single factor or trigger models and multifactorial models are discussed. It is suggested that in order to explain events in hominid evolution it is necessary to recognize that such events are produced by the interaction of factors acting as conditions, causes (selective pressures), constraints (often phylogenetic) and consequences. Within this framework a number of explanatory strategies are proposed. First, that the pattern of evolution can throw light on process; second, that the relationship between the pattern of hominid evolution and the context in which it occurs can be significant; third, that assessing general models in terms of the feasibility of the detailed biological parameters can be a powerful tool; fourth, that the selective advantages of hominid characteristics should consider both costs and benefits; and fifth, that the consequences of humans having evolved may help us to assess the underlying causes. These strategies lead to the conclusion that the pattern of human evolution is similar to that of other animals in consisting of a series of adaptive radiations. Climate influences hominid evolution, but does not lead to the appearance of new species. The primary effect is through extinction, implying that evolutionary novelty amongst hominids derives from local competitive conditions. The evolution of high levels of encephalization, whatever the proximate selective pressures, was only possible in the context of major changes in life history strategy and foraging behaviour. Finally, when the development of food production is linked to long-term evolutionary patterns, it can be seen that humans have been part of the most significant ecological change for 280 million years.