Models of changes in lineages of species, sub-species and individuals over time are presented. They can take account of variations in many factors including extinction and fossilisation rates, lineage splitting and joining patterns, migrations across barriers and back-migrations, effects of the existence of different types of characters, and differences in adult sex ratios and mating systems.
The results imply that fossils lie far more frequently on extinct lineages than usually assumed, that common ancestors are probably much further back in time than usually accepted, and that migrations occur far more frequently and at different time levels, than usually supposed. The results imply, too, that differences in adult sex ratio and mating patterns can have unexpected effects upon lineages.
Such findings may have especial implications for fossil studies attempting to assess time of common ancestry and for molecular studies of origins that use calibrations from fossils. They particularly imply that the common ancestry of humans and chimpanzees at 5MYA and modern human origins at 0.15MYA need to be viewed with caution. They suggest that population size (already known), adult sex ratio (two or three females-to-one in modern apes, but one-to-one in modern humans) and mating systems (obligate polygyny in modern apes, but facultative polygyny and monogamy in modern humans) may have major effects upon evolutionary relationships. They may, finally, provide better information about the complexity of "characters" and therefore improve understanding of cladistic analyses.
Thanks are due to Ken Wessen who invented the programmes used in this study. The work is supported by the Australian Research Council and the UK Leverhulme Trust.
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