Despite an immense amount of variation in organisms throughout the animal kingdom many of their genes show substantial conservation in DNA sequence and protein function. Here we explore the potential for a conserved evolutionary relationship between genes and their behavioural phenotypes. We investigate the evolutionary history of cGMP-dependent protein kinase (PKG) and its possible conserved function in food-related behaviours. First identified for its role in the foraging behaviour of fruit flies, the PKG encoded by the foraging gene has since been associated with the maturation of behaviour (from nurse to forager) in honey bees and the roaming and dwelling food-related locomotion in nematodes. These parallels encouraged us to construct protein phylogenies using 32 PKG sequences that include 19 species. Our analyses suggest five possible evolutionary histories that can explain the apparent conserved link between PKG and behaviour in fruit flies, honey bees and nematodes. Three of these raise the hypothesis that PKG influences the food-related behaviours of a wide variety of animals including vertebrates. Moreover, it appears that the PKG gene was duplicated some time between the evolution of nematodes and a common ancestor of vertebrates and insects whereby current evidence suggests only the for-like PKG might be associated with food-related behaviour.