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Creating the creators: if creation demands a visionary creator, then how does blind evolution manage to build such splendid new things as ourselves? - special issue: The Science of Creativity
Discover, Oct, 1996 by Stephen Jay Gould
Evolution works like the Nairobi market, not like the throwaway society of the wealthy West. You can evolve further only by using what you have m new and interesting ways. Organisms have no equivalent to currency for acquiring something truly new@ they can reconstruct only from their own innards.
If organisms could not reuse old material in strikingly new ways, how could evolution ever produce anything novel? This classical dilemma has a fancy name dating from mid-nineteenth century debates following the publication of Darwin's book: "The problem of the incipient stages of useful structures." I prefer a catchier label based on a primary example: "The 5 -percent-of-a-wing problem." To cite the defining case@ wings and feathers work wonderfully for flight; we can easily understand their adaptive function as fully developed organs. But how can a wing ever be constructed if evolution must pass through a long series of intermediary stages - for 5 percent of a wing confers no benefit whatsoever in flight. How can evolution ever build a bird's wing from the forearm of small running dinosaurs if early stages in the putative transition cannot function for flight at all?
In a brilliant resolution of this conundrum, Darwin proposed that organs explicitly adapted by natural selection for one function also possess latent potential for working in other ways, if later environmental shifts encourage such an evolutionary response. (This latent potential arises as a fortuitous consequence of structural design, not as a direct and explicit result of natural selection. Evolution can't anticipate an unknown future.) A row of feathers on a forearm (5 percent of a wing, so to speak) cannot aid flight, but feathers also work superbly as thermoregulatory devices for conserving heat. Thus, feathers may have evolved from reptilian scales for an initial function in thermoregulation - and only later were they co-opted for flight when they became numerous and elaborate enough to provide aerodynamic advantages. (Experimental studies on insect wings-where the same evolutionary problem applies - show that tiny wings confer thermodynamic but no aerodynamic benefits. In a sequence of increasing wing size, advantages for flight "kick in" just when further growth stops providing any additional thermodynamic benefits.) Thus, structures evolved to retain heat have a latent potential for use in flight - an originally unexpected capacity that may become important as the organs get more elaborate or as environmental conditions change. Much of evolutions novelty arises from the actualization of such latent potentials, not from slow and explicit improvement of an unchanged function by natural selection.
This principle of co-optation in the evolution of novel functions underlies much of evolutions quirkiness and tendency to change course in unpredictable ways. If an intelligent extraterrestrial had visited the late Triassic Earth and watched a small running dinosaur sparsely clad in forearm feathers that worked only for thermodynamic effect, could the spaceman possibly have foreseen a future Earth with 8,000 species of flying birds@ If an earlier visitor to the evolving Earthly zoo had seen a small lineage of fully aquatic fishes with lobeshaped fins evolved only for scuttling along the bottoms of ponds, could he have foreseen an entire history of vertebrate evolution on land, and the eventual transformation of the forward air into hands capable of sitting at a typewriter and composing this article?
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