This shows the color of pig, cow and whale muscles. The oxygen-storing protein myoglobin gives meat its red color. Elite diving mammals contain such high concentrations of myoglobin that their muscles look almost black. This image relates to a paper that appeared in the June 14, 2013, issue of Science, published by AAAS. The paper, by Scott Mirceta at University of Liverpool in Liverpool, UK, and colleagues was titled, "Evolution of Mammalian Diving Capacity Traced by Myoglobin Net Surface Charge."