argued for the anti-evolutionist prosecution in the Scopes Trial on the State of Tennessee law limiting the teaching of evolution. Tucker noted that Rudolph Franz Zallinger's 1965 "The Road to Homo Sapiens" fold-out illustration in F. Clark Howell's Early Man, showing a sequence of 14 walking figures ending with modern man, fitted the palaeoanthropological discoveries "not into a branching Darwinian scheme, but into the framework of the original Huxley diagram." Howell ruefully commented that the "powerful and emotional" graphic had overwhelmed his Darwinian text. Sliding between meanings Scientists, Ruse argues, continue to slide easily from one notion of progress to another: even committed Darwinians like Richard Dawkins embed the idea of cultural progress in a theory of cultural units, memes, that act much like genes. Dawkins can speak of "progressive rather than random ... trends in evolution". Dawkins and John Krebs deny the "earlier [Darwinian] prejudice" that there is anything "inherently progressive about evolution", but, Ruse argues, the feeling of progress comes from evolutionary arms races which remain in Dawkins's words "by far the most satisfactory explanation for the existence of the advanced and complex machinery that animals and plants possess". Ruse concludes his detailed analysis of the idea of Progress, meaning a progressionist philosophy, in evolutionary biology by stating that evolutionary thought came out of that philosophy. Before Darwin, Ruse argues, evolution was just a pseudoscience; Darwin made it respectable, but "only as popular science". "There it remained frozen, for nearly another hundred years", until mathematicians such as Fisher provided "both models and status", enabling evolutionary biologists to construct the modern synthesis of the 1930s and 1940s. That made biology a professional science, at the price of ejecting the notion of progress. That, Ruse argues, was a significant cost to "people [biologists] still firmly committed to Progress" as a philosophy. Facilitated variation Biology has largely rejected the idea that evolution is guided in any way, but the evolution of some features is indeed facilitated by the genes of the developmental-genetic toolkit studied in evolutionary developmental biology. An example is the development of wing pattern in some species of Heliconius butterfly, which have independently evolved similar patterns. These butterflies are Müllerian mimics of each other, so natural selection is the driving force, but their wing patterns, which arose in separate evolutionary events, are controlled by the same genes. See also Adaptive mutation Devolution Directed evolution (in protein engineering) Directed evolution