Aggression is an evolutionary conserved social behavior that is regulated by both environment and genetics. Understanding the neural and genetic basis of aggression is a major challenge in neurobiology especially since the extent of environmental and genetic contribution may vary between systems. A great deal of what we know about neurobiological differences in naturally occurring subordinate and dominant phenotypes comes from species in which social rank is reversible and based on the social environment. In this talk, I will present my previous work on Astatotilapia burtoni, an African cichlid with a socially controlled dominance hierarchy and well-characterized differences along the hypothalamic-pituitary-gonadal (HPG) axis. I will highlight differences between vasotocin and serotonin neurons in subordinate and dominant males and present a model for how their interactions could regulate aggression. With this background I will lead into my current research on the Ruff, Philomachus pugnax. In the Ruff, the evolution of a social system with three genetically determined male morphs was facilitated by an inversion event on an autosomal chromosome 3.8 million years ago. How did this chromosomal aberration lead to the distinct aggression profiles, mating strategies, breeding plumage and endocrinal profiles observed among the morphs? We are in a unique position to begin to answer these questions and discover neuroanatomical and gene expression differences across male morphs that will help us better understand their evolution.