 According to Schurz (2002), the difference between idealization conditions in physics and normality conditions in evolutionary sciences can be explained as follows: In physics, one traditionally thinks of complexity as a source of disorder—regularities are obtained by abstracting away from complexities. In evolutionary systems, by contrast, complexity is usually a source of order—complexity which has been selected by evolution to stabilize normic behavior. As Wachbroit (1994, 587f.) puts it, ideal planets are theoretical abstractions: mass points under the influence of a centripetal force and ‘nothing else’. They do not literally exist. In contrast, normal birds really do exist because they are what has been selected through evolution. When speaking of a normal bird, we do not abstract from its admirable complexity, but we rely on it as the cause of its normal behavior. This does not mean that abstract laws of physics (e.g., the laws of aerodynamics) play no role in the explanation of functional behaviors of evolutionary systems (e.g., that birds can fly). However, even when we explain a bird’s flying ability in terms of the laws of aerodynamics, we still have to assume a ‘normal’ bird which possesses the typical capabilities of birds that have been selected through evolution. The idealization procedures needed for planets would not make good sense for birds: there are no disturbing parameters which, when going to zero, turn a real bird into an ideal bird which can necessarily fly and which is approximated by the real bird.