My general interest is in the evolution of complex traits. I focus predominantly on two topics within this field. First is the effect that the structure of the genotype-phenotype maps has on the evolvability of phenotypes. Here I’m particularly interested in the effects of two aspects of the genotype-phenotype map, the multifunctionality of genes (pleiotropy) and the gene interaction (epistasis). The second topic is the evolution of the genotype-phenotype map itself and in particular the evolution of pleiotropy. Pleiotropy reflects the integration of developmental and functional processes. The evolution of integration (and thus of development) is most often addressed by comparative studies. My approach is different in that I study the populational variation in pleiotropy, the raw material for its evolution. Currently, I focus on the mechanistic basis of this variation, and its contribution to the evolutionary trait differentiation. This work links population genetic with developmental and physiological processes.