Back in Feb 2009, the hypothesis of front-loading evolution allowed me to raise an unconventional perspective on convergence – perhaps many examples of convergence are a consequence of intrinsic constraints rather than purely environmental factors.
Then in June 2009, I added some more support to this prediction in the form of a mitochondrial protein called Tom40. Then I added a ribosomal protein. Then in Jan 2010, there was more support, this time in the form of prestin. A couple of months later, more support came from the VEGF receptors. Again and again, examples of convergence were being explained by factors intrinsic to organisms (preadaptations) and not merely the environment and similar selection pressures.
And let’s not forget that last month, I noted yet another striking example of support:
“The oxygen transport hemoglobins that were independently invented by the jawed and jawless vertebrates are functionally quite similar, but there are numerous structural details that belie their independent origins,” Storz said. “These small but telling differences reflect the fact that the proteins evolved their oxygen-transport function from different ancestral starting points.
The hemoglobins of jawed and jawless vertebrates were independently invented, yet they are homologous at a deeper level, as both are built around the globin fold.
This tends to confirm a point I made in my book:
The crucial point is that if a designer introduced cytochromes/globins into the original cells, they would not be surprised at all to fi nd that a mammal-like creature, evolving billions of years later, also “just happened” to have built their circulatory systems around it. In fact, this may very well be what their models would have predicted.
The lamprey hemoglobin is part of the globin superfamily. Thus, one could argue that once the globin-fold emerged and associated with heme, it was only a matter of time before it would be put to use for O2 binding and delivery purposes. That is, the globin-fold itself is a preadaptation and it is this preadaptative state that restricts possibilities as evolution is much more likely to tap into and exploit this poised, pre-existing state than stumble upon some other possible solution that would be harder to reach. In other words, a significant factor to convergence can be attributed to deep homology, where ancient ancestral states effectively “constrain” where evolution goes.
The case for front-loading not only gets stronger, but for those able to focus, it is starting to separate itself from conventional, non-teleological views. Non-teleological thinking led evolutionary biologists to resist and deny deep homology; front-loading predicts it. Non-teleological thinking attributes convergence to the environment (since the environment is the designer); front-loading expects an intrinsic dimension, where deep homology constrains evolution by functioning as a preadaptation.
Evolution is not something that “just happens.” It’s looking more and more like it was not only designed to happen, but designed to happen in a certain way.