Selection on multiple characters

So far we’ve studied only the evolution of a single trait, e.g., height or weight. But organisms have many traits, and they evolve at the same time. How can we understand their simultaneous evolution? The basic framework of the quantitative genetic approach was first outlined by Russ Lande and Steve Arnold [2]. Let z1, z2, . . . , zn be the phenotype of each character that we are studying. We’ll use z̄ to denote the vector of these characters before selection and z̄∗ to denote the vector after selection. The selection differential, s, is also a vector given by