Abstract
The key to understanding species variation in neuroendocrine controlling mechanisms lies in understanding the constraints that have given rise to diverse reproductive patterns. Recent research clearly shows that species evolving under different constraints exhibit different patterns of reproduction and have fundamentally different neuroendocrine mechanisms controlling reproduction. Diversity can be exploited profitably by those interested in the fundamental nature of biobehavioral mechanisms. The comparative approach also promises to increase our understanding of broader intellectual and theoretical issues in behavioral endocrinology.