Sociobiology: The New Synthesis (1975; 25th anniversary edition 2000) is a book by E. O. Wilson that helped start the sociobiology debate, one of the great scientific controversies in biology of the 20th century (see Criticism of evolutionary psychology). Wilson popularized the term "sociobiology" as an attempt to explain the evolutionary mechanics behind social behaviors such as altruism, aggression, and nurturance. 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.