Life on Earth resulted in an astonishing diversity of form and phenotype. But our understanding on how this diversity is generated as a result of historical processes is still limited. We use a highly interdisciplinary approach that integrates development, ecology and population genetics to unravel the mechanistic changes that give rise to evolutionary alterations and novelty (Sommer, 2009). For this to be achieved well-selected model organisms with a sophisticated analytical toolkit for functional investigations have to be developed. We have established the free-living nematode Pristionchus pacificus as a model system in evolutionary biology. P. pacificus combines in a unique manner, laboratory studies building on genetic, genomic and transgenic tools with field work in ecology and population genetics.