Book excerpt: An overview of the extensive and frequently controversial literature on communally breeding birds developed since the early 1960s, when students of evolution began to examine sociality as a product of natural selection. Jerram Brown provides original data from his own theoretical and empirical studies and summarizes the wide array of results and interpretations made by others. Originally published in 1987. The Princeton Legacy Library uses the latest print-on-demand technology to again make available previously out-of-print books from the distinguished backlist of Princeton University Press. These editions preserve the original texts of these important books while presenting them in durable paperback and hardcover editions. The goal of the Princeton Legacy Library is to vastly increase access to the rich scholarly heritage found in the thousands of books published by Princeton University Press since its founding in 1905.