A matter of evolutionary life and death : an ecological model of growth and development in Homo erectus
This thesis investigates the evolutionary ecology of Homo erectus, focussing on the differential impact of the environment on the species' life history strategy. Departing from previous studies in taking an integrated approach, it examines the related factors of age-specific mortality, encephalisation, and the rate and energetic burden of growth, in order to identify the mechanism by which H. erectus adapted to a diverse range of climates and environments, and how thoroughly that adaptation was achieved. An exploration of the environmental tolerance of H erectus is framed within a model that shows regions that comprised the core of the species, where tolerance is highest and conditions are optimum for growth and reproduction, and periphery regions which fall towards the extremes of tolerance and have repercussive effects on encephalisation, juvenile mortality and growth. Life history traits should vary accordingly, allowing the development of a model for the relationship between environmental variation and the differential evolution of H. erectus. The work is organised thematically. Having provided an overview of evolutionary ecology and introduced the concept of paleo-demes as a means of organising, grouping and understanding the fossils of H. erectus, I address the shortcomings of the r-K dichotomy with a study of age-specific mortality. This work is then applied to patterns of encephalisation, and the energetic implications bf increasing brain size are addressed. A comparative study of two modern human populations supports the prediction that stability of environment translates into stability of growth, and these findings are applied to H. erectus. I demonstrate that H erectus exhibited a long-term trend of an increasing cranial capacity, but that this was not uniform across the species and had varying success, with subsequent energetic stress in the young resulting in high juvenile mortality in some areas. I conclude that the model of core and periphery relates to the latitude of the environment, and that H. erectus was an adaptable and flexible species with a number of strategies available to maximise survival in a range of environmental conditions.