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Tuesday, February 05, 2008

Evolution as Tinkering

François Jacob won the Nobel Prize in 1965 for his work on the lac operon. He is also known for his thoughts on evolution, especially the concept of a tinkerer. The idea deserves to be better known so I present a long quotation from his little book The possible and the Actual published in 1994. The book contains a lecture that was based on an article he published in Science back in 1977 (Jacob, 1977).

I'm a big fan of this view of evolution [Evolution by Accident].
The action of natural selection has often been compared to that of an engineer. This comparison, however, does not seem suitable. First, in contrast to what occurs during evolution, the engineer works according to a preconceived plan. Second, an engineer who prepares a new structure does not necessarily work from older ones. he electric bulb does not derive from the candle, nor does the jet engine descend from the internal combustion engine. To produce something new, the engineer has at his disposal original blueprints drawn for that particular occasion, materials and machines specially prepared for that task. Finally, the objects thus produced de novo by the engineer, at least by a good engineer, reach the level of perfection made possible by the technology of the time.

In contrast, evolution is far from perfection, as was repeatedly stressed by Darwin, who had to fight against the argument from perfect creation. In the Origin of Species, Darwin emphasizes over and over again the structural and functional imperfections in the world. He always points out the oddities, the strange solutions that a reasonable God would never have used.

In contrast to the engineer, evolution does not produce innovations from scratch. It works on what already exists, either transforming a system to give it a new function or combining several systems to produce a more complex one. Natural selection has no analogy with any aspect of human behavior. If one wanted to use a comparison, however, one would have to say that this process resembles not engineering but tinkering, bricolage we say in French.

While the engineer's work relies on his having the raw materials and the tools that exactly fit his project, the tinkerer manages with odds and ends. Often without even knowing what he is going to produce, he uses whatever he finds around him, old cardboards, pieces of string, fragments of wood or metal, to make some kind of workable object. As pointed out by Claude Levi-Strauss, none of the materials at the tinkerer's disposal has a precise and definite function. Each can be used in several different ways. What the tinkerer ultimately produces is often related to no special project. It merely results from a series of contingent events, from all the opportunities he has to enrich his stock with leftovers. In contrast with the engineer's tools, those of the tinkerer cannot be defined by a a project. What can be said about an of these objects is that "it could be of some use." For what? That depends on the circumstances.

In some respects, the evolutionary derivation of living organisms resembles this mode of operation. In many instances, and without any well-defined long-term project, the tinkerer picks up an object which happens to be in his stock and gives it an unexpected function. Out of an old car wheel, he will make a fan; from a broken table, a parasol. This process is not very different from what evolution performs when it turns a leg into a wing, or a part of a jaw into pieces of ear.

...

When different engineers tackle the same problem, they are likely to end up with very nearly the same solution: all cars look alike, as do all cameras and all fountain pens. In contrast, different tinkerers interested in the same problem will reach different solutions, depending on the opportunities available to each of them. This variety of solutions also applies to the products of evolution, as is shown, for instance, by the diversity of eyes found throughout the living world. The possession of light receptors confers a great advantage under a variety of conditions. During evolution, many types of eyes appeared, based on at least three different principles: the lens, the pinhole, and multiple holes. The most sophisticated ones, like ours, are lens-based eyes, which provide information not only on the intensity of incoming light but also on the objects that light comes from, on their shape, color, position, motion, speed, distance, and so forth. Such sophisticated structures are necessarily complex.

One might suppose, therefore, that there is just one way of producing such a structure. But this is not the case. Eyes with lenses have appeared in molluscs and in vertebrates. Nothing looks so much like our eye as the octopus eye. Yet it did not evolve the same way. In vertebrates, the photoreceptor cells of the retina point away from the light while in molluscs they point toward the light. Among the many solutions found to the problem of photoreceptors, these two are similar but not identical. In each case, natural selection did what it could with the materials at its disposal.
For a more up-to-date view of the evolution of eyes see PZ Myers' article in the current (January/February 2008) issue of SEED magazine.


Jacob, F. (1977) Evolution and Tinkering. Science 196:1161-1166. ]JSTOR]

Jacob, F. (1994) from The Possible and the Actual, reprinted in Evolution Extended, Connie Barlow ed. MIT Press, Cambridge, MA (USA) 1994.

1 comment :

  1. The metaphor of tinkering conveys valuable "lessons" because it conveys non-adaptive constraints of previous materials (although in an ultimately adaptive context)
    The notion of tinkering is even clear enough that we can easily serve examples: lots of tinkering is going on in evolution. However, as a vision of ALL of evolution, tinkering conveys an image that seems still too adaptationist to me: as if organisms were all about problem-solving. Many an evolutionary phenomenon is not an example of tinkering. Let tinkering be tinkering: It's a nice, valuable idea, but as general philosophy,it is insufficient and inadequate to understand biology and evolution.

    BTW Kudos to jacob, everyone should read the logic of life. Biologits should know exactly ewhere do their ideas come form. Very entertaining narration of the history of biological thinking (despite it's "gene triumphalism").

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