Major life-history transitions by deterministic directional natural selection

For large-scale evolution on Earth there has been a directional change where simple self-replicators evolved into large organisms with high metabolic rates and long pre-reproductive periods. Associated with this increase there have been major life-history transitions from asomatic, non-senescing, haploid, and asexually reproducing organisms to somatic, senescing, diploid, and sexually reproducing organisms with male and female individuals. Using a game theoretical model, it is shown that this trajectory can be explained by deterministic natural selection as it arises from first principles of the self-replication process in mobile organisms. It is shown (i) that selection for an increase in the energetic state of the organism puts a direction to evolution, (ii) that selection by density-dependent competitive interactions can explain the major life-history transitions as a function of the energetic state of the organism, and (iii) that the two selection processes combined can explain an exponentially increasing body mass. It is also shown (iv) why, for the case with an increasing body mass, we may expect many life histories to evolve in accordance with the exponents of the body mass allometries, (v) that an upper constraint on the body mass and metabolic rate can induce an additional transition into eusocial communities, and (vi) that the evolutionary trajectory is likely reversible with backward evolution during periods of environmental crises. (C) 2003 Elsevier Ltd. All rights reserved.