Original Scientific Article

Evolution: Education and Outreach

, Volume 1, Issue 4, pp 358-389

First online:

The Evolution of Complex Organs

  • T. Ryan GregoryAffiliated withDepartment of Integrative Biology, University of Guelph Email author 


The origin of complex biological structures has long been a subject of interest and debate. Two centuries ago, natural explanations for their occurrence were considered inconceivable. However, 150 years of scientific investigation have yielded a conceptual framework, abundant data, and a range of analytical tools capable of addressing this question. This article reviews the various direct and indirect evolutionary processes that contribute to the origins of complex organs. The evolution of eyes is used as a case study to illustrate these concepts, and several of the most common misconceptions about complex organ evolution are discussed.


Adaptation Constraints Convergence Co-option Crystallin Duplication Exaptation Eye Functional shift Historical contingency Lens Natural selection Opsin Photoreceptor