This shows striking variation between breeds of domestic pigeons. Left: Old German owl breed with a head crest and short beak. Right: Scandaroon breed with large beak and no crest. Background: Classification scheme for domestic pigeon breeds proposed by Charles Darwin in 1868. This image relates to a paper that appeared in the Jan. 31, 2013, issue of Science Express, published by AAAS. The paper, by Michael Shapiroat University of Utah in Salt Lake City, Utah, and colleagues was titled, "Genomic Diversity and Evolution of the Head Crest in the Rock Pigeon."