Homoplasy and developmental constraint: A model and an example from plants

SYNOPSIS. Much attention has been paid to the role of developmental information in estimating phylogenetic relationships and, more recently, to the use of phylog-enies in understanding the evolution of development. At the moment, however, we lack a sufficiently general theory connecting phylogenetic patterns of character evolution to properties of developmental systems. Here we outline a simple model relating homoplasy to the rate of character change and the number of evolvable states, both of which may reflect developmental constraints. Given a particular rate of character change, the fewer the evolvable states the more homoplasy is expected, and vice versa. The repeated evolution of a limited number of forms of bilateral flower symmetry may reflect constraints imposed by overall flower ori-entation and underlying mechanisms of differentiation