Re design skill, Maynard Smith writes:
"It seems to be a general feature of evolution that new functions are performed by organs which arise, not *de novo*, but as modifications of pre-existing organs. Our teeth are modified scales, our ear ossicles modified jaw bones, our arms modified fins, mammae are modified sweat glands, and so on. If evolution proceeds by a series of small changes, it is hard to see how it could be otherwise. "The natural conclusion, then, is that the basic body plans of the different phyla represent structures, which adapted some ancestral form ot a particular way of life, and which have since been modified to serve different functions. Why, the, has the basic plan been preserved when habits and ways of life have altered? An engineer designing a horseless carriage is not obliged to retain structural features that existed solely to adapt the carriage to the horse (though in fact such primitive features were retained for a time). In evolution, structures are conservative because changes must be made one step at a time, each step being an improvement on the preceeding one. Such stepwise change does not permit radical restructuring."
As JMS himself recognizes, this step wise engineering conception of evolution seems to downplay the role of chance events:
"The main proponent of the idea that chance events in small populations are crucial in evolution is Sewall Wright, the only surviving member of the great triumvirate (with RA Fisher and JBS Haldane) who founded population genetics. Because of the accident that Wright is American, whereas Fisher and Haldane were British, evolutionary biologists often place great emphasis on chance events, whereas we British know better."
>From the Problems of Biology. Oxford, 1986
rb