[From friend of the podcast Adam Arnold]
In regards to the latest episode on Candide and the continuing discussion of scientism and evolution on the blog, it is interesting to look back on the classic article by Stephen Jay Gould and Richard Lewontin on the "adaptationist programme" in evolutionary biology. In "The spandrels of San Marco and the Panglossian paradigm: a critique of the adaptationist programme", Gould and Lewontin take on what they consider the dominant view in evolutionary biology at the time:
...based on faith in the power of natural selection as an optimizing agent. It proceeds by breaking an organism into unitary 'traits' and proposing an adaptive story for each considered separately. Trade-offs among competing selective demands exert the only break upon perfection; non-optimality is thereby rendered as a result of adapatation as well. [Proceedings of the Royal Society of London, p. 581]
Gould and Lewontin champion an alternative view which proposes to look at organisms as integrated wholes and consider the forces which constrain development - the architecture of their heritage - as more selective an interesting. They are warning against focusing on the particular what instead of the overall why. They illustrate this beautifully with an example in comparing the “adaptationist program” in evolutionary biology to that of Voltaire's Liebnizian Dr. Pangloss:
Such architectural constraints abound and we find them easy to understand because we do not impose our biological biases upon them. Every fan vaulted ceiling must have a series of open spaces along the mid-line of the vault, where the sides of the fans intersect between the pillars. Since the spaces must exist, they are often used for ingenious ornamental effect. In King's College Chapel in Cambridge, for example, the spaces contain bosses alternately embellished with the Tudor rose and portcullis. In as sense, this design represents an 'adaptation', but the architectural constraints is clearly primary. The spaces arise as a necessary by-product of fan vaulting; their appropriate use is secondary effect. Anyone who tried to argue that the structure exists because the alternation of rose and portcullis makes so much sense in a Tudor chapel would be inviting the same ridicule that Voltaire heaped on Dr Pangloss: 'Things cannot be other than they are... Everything is made for the best purpose. Our noses were made to carry spectacles, so we have spectacles. Legs were clearly intended for breeches, and we wear them.' Yet evolutionary biologists, in their tendency to focus exclusively on immediate adaptation to local conditions, do tend to ignore architectural constraints and perform just such an inversion of explanation. [ibid, pp. 582-3]
If this diagnosis of Gould and Lewontin is (was) correct, it is frightening that our so-called enlightened natural science can slip back so easily into a mythology of a Leibnizian Theodicy; even more so in such an unconscious fashion.
The natural sciences are doing fine. A few points: First, biologists are well aware of ‘architectural constraints’ and actually use them as one of the most powerful signals of a selective event. When a beneficial mutation arises in a particular part of the genome, and undergoes strong selection, it will soon increase in frequency and sweep through a population. A byproduct of this is that the surrounding regions of DNA get carried along. This is called a selective sweep, and the signature it leaves is a region of the genome with dramatically lowered allelic diversity flanking a single beneficial mutation (all the original diversity in the flanking regions have been replaced, even though this replacement may be functionally irrelevant).
Second, any principled distinction between spandrels and adapted features is missing the point, as far as natural selection is concerned. Natural selection has no memory: a feature that arose as an adaptation can become a spandrel (appendix, anyone?) and a spandrel can become an adaptation (remember the bones in your inner ear? originally spandrels derived from jawbone development in our distant vertebrate ancestors).
I think evolutionary biology is more conscious of the possibility of making this error, and more careful to avoid making it, than evolutionary psychology (or as it was called in Gould’s time, “sociobiology”) – if you keep up to date on the type of research in that field that trickles up to the popular science press, you’ll notice that practically ever other paper makes this fundamental mistake.