Published online by Cambridge University Press: 01 January 2022
Evolutionary models can explain the dynamics of populations, how genetic, genotypic, or phenotypic frequencies change with time. Models incorporating chance, or drift, predict specific patterns of change. These are illustrated using classic work on blood types by Cavalli-Sforza and his collaborators in the Parma Valley of Italy, in which the theoretically predicted patterns are exhibited in human populations. These data and the models display properties of ensembles of populations. The explanatory problem needs to be understood in terms of how likely an observed change, in either a population or an ensemble, would be under drift alone; this is fundamentally a matter of chance. Understood in this way, issues of drift and chance undercut most recent philosophical, but not biological, discussions of the role of “genetic drift.”
I have been fortunate enough to discuss these issues, over many years, with a number of colleagues, including John Beatty, Robert Brandon, Richard Burian, Paul Davies, Roberta Millstein, Thomas Polger, and Robert Skipper. Thomas Kane in particular led me to look at the work by Cavalli-Sforza and did a great deal in shaping my thinking. Finally, I am grateful for the support of the Taft Faculty Committee at various stages of my work.