Rational Egoist writes: "Researchers at Yale University have found that some of the brightest colors in bird feathers are created through structures similar in origin and composition to that of beer foam. Unlike with most colors in nature — which are produced by pigments — the bright blue colors of Bluebirds and Blue Jays are actually produced by sponge-like nanostructures. These structures are formed in quite the same way as beer foam. From the article: "[Researchers] compared the nanostructures to examples of materials undergoing phase separation, in which mixtures of different substances become unstable and separate from one another, such as the carbon-dioxide bubbles that form when the top is popped off a bubbly drink. They found that the color-producing structures in feathers appear to self-assemble in much the same manner. Bubbles of water form in a protein-rich soup inside the living cell and are replaced with air as the feather grows.""