Venom from the western diamondback rattlesnake (Crotalus atrox) contains a toxic protein that targets blood vessels walls and kills tissue, earning it and similar toxins the nickname of "meat tenderizer." By analyzing the sequences of amino acids that make up such toxins in related species of snakes, Stephen Mackessy of the University of Northern Colorado in Greeley and his colleagues found that the amino acid sequence changes more rapidly in certain regions (red) and less frequently in other regions (yellow) compared with the rest of the protein (white). Highly changeable regions enable toxins to diversify more quickly, the team proposes. Credit: R. Doley et al./BMC Evolutionary Biology 2009