One of the founding elements of this evo-devo discipline is the persistence of the same genes in animals as different as vertebrates and invertebrates are. Much of the difference between these animals must therefore depend on how these genes are used, rather than on their structures.
In this second lecture, we consider the various main possibilities for variation in gene regulation, i.e. variations in time (heterochronies), space (heterotopias), quantity (heterometries) or type (heterotypies). For each of these possibilities, examples are discussed, drawing on recent work, but all directly related to historical milestones in either evolution (Darwin's finch beaks) or development (homeotic variations in mammals). The emphasis is on the potential importance of changes in gene regulation to produce new structures or modify morphologies.
