Phylogeny, models and inference

Elizabeth Alison Thompson

The aim of this book is to provide a method of solution to a specific problem, and yet one which has attracted a wide interest in recent years. This is the problem of the statistical assessment of the phylogenetic relationships between various ethnic groups within the human species, on the basis of genetic data currently available in present-day populations. The basic difference between the approach to be considered here and that of some previous approaches is that inferences are to be based on a probabilistic model for the genetic evolution of the populations under consideration. The criteria of likelihood inference are to be used to assess alternative hypotheses of evolutionary history. No model can cover all aspects of the complex process of evolution, and inferences are necessarily made within the framework of the model. However statistical inferences cannot be made in the absence of a model, and, even if this model is necessarily a simplification of the true situation, an explicit statement of the assumptions under which inferences are made enables the effect of such assumptions and the possibilities of extending the model to be considered.

We shall consider only the problem of making inferences concerning several, often large, populations within the human species, these populations having a common source but having evolved largely independently, there being little interchance between them. Population differences reflect the length of time since the existence of a common ancestral population, and an evolutionary tree model is required. Some specific problems of population admixture may also be analysed on the basis of a model of independently evolving populations, and one such is considered in Chapter 6, but we shall not consider more generally the analysis of relationships between smaller populations where the pattern of differentiation depends mainly on the interchange between them and where migration has been sufficient for them to evolve substantially as a single unit.

Fonte: Thompson, E. A. 1975. Human evolutionary trees. Cambridge, CUP.