Well into the age of genetic engineering and cloning, the Darwinian debate continues, and few other scientists have done such concentrated work in elucidating the mechanism of evolution--and thus shedding light on that debate--as Francisco J. Ayala. Ayala has made vital contributions to the modern theory of evolution, both by theory and experiment, examining the rates and patterns of molecular evolution, the causes of genetic polymorphism (the ability of two or more distinct forms of an organism to coexist in the same interbreeding population) or gene mutation (changes in the hereditary material) in one species, the importance of natural selection versus random selection, as well as the role that reproductive isolation and environment play on population growth. Additionally, Ayala has been a major voice in the philosophical and ethical issues related to the study of human evolution.

Francisco Jose Ayala was born in Madrid, Spain, the son of...