[A] skyhook is ... an exception to the principle that all design, and apparent design, is ultimately the result of mindless, motiveless mechanicity. A crane, in contrast, is a subprocess or special feature of a design process that can be demonstrated to permit the local speeding up of the basic, slow process of natural selection, and that can be demonstrated to be itself the predictable (or retroactively explicable) product of the basic process. ... [T]he physicist Steven Weinberg, in Dreams of a Final Theory (1992) ... distinguishes between uncompromising reductionism (a bad thing) and compromising reductionism (which he ringingly endorses). Here is my own version. We must distinguish reductionism, which is in general a good thing, from greedy reductionism, which is not. The difference, in the context of Darwin's theory, is simple: greedy reductionists think that everything can be explained without cranes; good reductionists think that everything can be explained without skyhooks.