Gregor Mendel developed the laws of genetics by cross-breeding peas and observing how characteristics were passed from parent to offspring. Our understanding of recessive and dominant genetic traits was worked out by Mendel well before the discovery of DNA. In this sense, Mendel can be seen as a bridge: Darwin described evolution, Mendel found the principles of heredity, and DNA provided the mechanism of evolution through heredity.

Photo: Jenn Forman Orth, http://www.flickr.com/photos/urtica/22912567/. Licensed under Creative Commons Attribution-Noncommercial-Share Alike 2.0 Generic