The basis for a non-teleological perspective of evolution could have turned out to be much, much stronger. But it didn’t. As we have seen, Darwin’s insistence on strict gradualism was an important pillar for the non-teleological perspective, but we now know such strict gradualism is not necessary for evolution. We also saw that the non-telic perspective did not expect deep homology in developmental genes. For example, according to the non-telic viewpoint, the legs of flies and mice evolved independently simply because the environment would provide a strong selection pressure to build some type of leg. It would not matter what it was made of and it would not matter how it was constructed. All that would matter is that it functioned as a “leg.”
In other words, if Darwin would have turned out to be correct in his insistence on strict gradualism, and if analogous structures had turned out to be built from independently assembled pathways that were completely different, the basis for the non-telic perspective of evolution would be very strong, perhaps compelling us to prefer the Duck over the Rabbbit.
Let me now introduce a third place where the basis for the non-teleological perspective of evolution is drained of power.
Quoting some more from Adam Wilkins’s paper, “Between ‘‘design’’ and ‘‘bricolage’’: Genetic networks, levels of selection, and adaptive evolution”:
Although the metaphor of bricolage seems far more appropriate for describing the evolutionary process than design, it too is somewhat misleading. It implies a higher degree of freedom about the elements that are borrowed and used in new evolutionary ways than is probably the case. The verb in French, ‘‘bricoler,’’ often connotes an almost haphazard throwing of things together to see what happens and what works rather than the slightly more methodical procedure one associates with the term ‘‘tinkerer.’’
Indeed. If the bricolage metaphor was accurate, it would entail an almost haphazard throwing of things together to see what happens and what works. And if evolution really worked this way, then the non-teleological perspective would be on even more solid ground. In fact, it would fit nicely with the non-telic notions of strict gradualism and no deep homology. The bricolage metaphor would have us think that all genes are equally cooptable into all possible new functions. But that’s unlikely to be the case. In fact, Wilkins identifies two intrinsic factors, that I myself have previously tagged, that steer evolution away from such bricolage:
Although there are no experimental studies yet of the constraints involved in gene recruitment, consideration of the basic properties of the properties of molecules and of the requirements of the process suggest that there are two kinds of general constraint that must operate. The first is the set of preexisting properties of the recruited molecule, permitting its adoption for new roles. When a transcription factor (TF) is evolutionarily recruited for a new activity (25, 27), it must possess certain properties that confer capability for the new function, properties not shared with many other TFs. In effect, not any TF has equal potential for turning on, or repressing, a new gene or set of genes; the gain-of-function activity that a TF gene recruitment event comprises is determined by both the structure of the TF and the TF-binding sites in the enhancers of the target gene(s) (28, 29).
I have long noted that the preexisting properties of the recruited molecule would impose some form of direction on evolution. In fact, recently I identified such properties as nudges (see here and here). When this is coupled to deep homology, which puts the recruited molecules closer and closer to the original cells (the design event?), along with the way gene duplication, as a major source of evolution, facilitate recruitment while forwarding designs into the future (as explained in The Design Matrix, pp. 164-167), we can begin to appreciate why a teleological view of evolution is becoming increasingly plausible.
What’s more, I should also mention that several years ago, I raised the possibility of determining gene cooption frequencies. When Wilkins writes, “In effect, not any TF has equal potential for turning on, or repressing, a new gene or set of genes,” not only does this steer us away from bricolage, but it suggests we might be able to indirectly determine that some genes are more cooptable for certain functions as opposed to other genes. If we could measure this, we would have a more clear picture of where the nudges are.
Second, the recruited gene must be already expressed in the cell/tissue where its new function initially takes place, or the mutation that leads to the recruitment event is one that prompts the de novo expression of the recruited TF, making it available for a new use. In the latter cases, presumably additional mutations would be required to optimize the expression or the function (or both) of the recruited molecule. There is, as yet, no direct evidence for such optimization after recruitment, but it seems an unavoidable conclusion from what is known about structure–function relationships in regulatory macromolecules.
Again, in The Design Matrix, I spell out how location can be coupled with multi-functional proteins to unleash front-loaded potential. If you think about it, this would involve a synergy between the evolution of a metazoan state and front-loading. If the metazoan state was front-loaded, once it began to emerge, the state itself would open up new contexts for the activity of genes and thus facilitate the unpacking of any buried designs.
Anyway, to sum it up thus far:
Wilkins proposes two kinds of general constraint on evolutionary trajectories that I myself have noted before. These constraints would work hand-in-hand with front-loading, where the properties of the molecules-to-be-recruited would function as nudges, and the new contexts for gene expression would not only serve as further constraint, but also nudge the unpacking of buried designs.
At the very least, consider this. The non-teleological view of evolution could be much stronger than it really is. Strict gradualism, rampant bricolage, all coupled with the blind watchmaker having no dependence on any deep homology all makefor a most wondrous Duck. If that’s how evolution worked, it would be hard to make the case that front-loading is plausible. But since that is not how evolution works, it is hard to make the case the front-loading is implausible.