Sociobiology: The New Synthesis (1975; 25th anniversary edition 2000) is a book by the biologist E. O. Wilson. It helped start the sociobiology debate, one of the great scientific controversies in biology of the 20th century and part of the wider debate about evolutionary psychology and the modern synthesis of evolutionary biology. Wilson popularized the term "sociobiology" as an attempt to explain the evolutionary mechanics behind social behaviour such as altruism, aggression, and the nurturing of the young. It formed a position within the long-running nature versus nurture debate. The fundamental principle guiding sociobiology is that an organism's evolutionary success is measured by the extent to which its genes are represented in the next generation.