A recent article in Trends in Genetics, “Causes and evolutionary significance of genetic convergence,” addresses the apparently “convergent” appearance of genes or gene sequences and how unguided evolution can explain this. The paper defines convergence as the “independent appearance of the same trait in different lineages.” Thus, genetic convergence is the independent appearance of the same genetic trait in different lineages. The article starts by explaining how widespread convergent evolution is:
The recent wide use of genetic and/or phylogenetic approaches has uncovered diverse examples of repeated evolution of adaptive traits including the multiple appearances of eyes, echolocation in bats and dolphins, pigmentation modifications in vertebrates, mimicry in butterflies for mutualistic interactions, convergence of some flower traits in plants, and multiple independent evolution of particular protein properties.
(Pascal-Antoine Christin, Daniel M. Weinreich, and Guillaume Besnard, “Causes and evolutionary significance of genetic convergence,” Trends in Genetics, Vol.26(9):400-405 (2010) (internal citations omitted).)
But what causes these similar traits to appear in widely diverse organisms? It turns out that “convergent” phenotypic similarity is often based upon “convergent” genetic similarity: “studies have traced phenotypic convergence to modifications of homologous genes; in this paper such phenomena will be further referred to as convergent recruitment” (emphasis added; internal citations omitted). Or, as the abstract states:
Asccumulating studies on this topic have reported surprising cases of convergent evolution at the molecular level, ranging from gene families being recurrently recruited to identical amino acid replacements in distant lineages. (emphasis added)
In other words, as the paper explains, convergent phenotypic traits occur due to convergent genetic evolution, which supposedly “results from a strongly biased potential for a given phenotypic change as a consequence of mutations in different genes.”
Neo-Darwinian evolution isn’t supposed to be goal-directed, but some force is causing the same sequences–at the genetic level–to appear independently over and over again. In an undesigned world, this is extremely unlikely.
Though the authors of course do not advocate any sort of purpose behind evolution, their paper’s teleological language about the “potential” or “predisposition” for beneficial evolutionary change is striking (all emphases added):
- “Convergent recruitment of the same gene lineage from multigene families affords an ideal system for studying the predisposition of particular genes for a given novel function.”
- “We predict that, compared to the other members of the gene family, a recurrently recruited gene lineage will generally have a catalytic activity and an expression pattern closer to those needed for the novel reaction compared to other members of the same gene family.
- convergent recruitment suggest [sic] that only a few genes have the potential to create a specific phenotypic change”
In keeping with this teleological theme, the paper even alludes to the notion of pre-adaptation:
[G]enes must meet two broad criteria to be eligible for a novel function: (i) they must have the possibility of being recruited for a new task without deleterious effect due to the loss or modification of the ancestral function, and (ii) their expression profiles and kinetics must be suitable for the new task.
The paper explains that
[r]egarding the second criterion, the pool of candidates for a new function is likely to be limited to genes encoding enzymes with compatible catalytic properties or to genes that can acquire them via successive substitutions without strongly deleterious transitional stages . . . Transitions to proteins with better suited kinetics but which involve transitional stages with lower fitness are less likely to take place, and evolutionary paths that lead to optimized enzymes via successively advantageous single nucleotide substitutions will be more frequently followed.
If functional genetic pathways to new useful phenotypes are so fraught with peril, then the authors are faced with the reality that “[c]onvergent recruitment indicates that genes suitable for creating a given phenotype are rare.” Or, as the article’s abstract states: “molecular evolution is in some cases strongly constrained by a combination of limited genetic material suitable for new functions and a restricted number of substitutions that can confer specific enzymatic properties.”
The view that there are severely limited functional phenotypes is echoed by George R. McGhee in his book The Geometry of Evolution: Adaptive Landscapes and Theoretical Morphospaces: “convergent evolution means that there are a limited number of ways of making a living in nature, a limited number of ways of functioning well in any particular environment.” (p. 34)
We’re now left with a striking situation. Apparently “rare” genes that are “suitable” can only undergo a “restricted number of substitutions” in order to find one of a “limited number of ways of functioning.” If neo-Darwinism has difficulty finding functional gene sequences once, how is it stumbling upon the same gene sequences over and over again?
Is there a better explanation for why similar gene sequences appear over and over again in different organisms, even when common ancestry cannot suffice as the explanation? What known cause can do this? Stephen C. Meyer suggests one:
Agents can arrange matter with distant goals in mind. In their use of language, they routinely ‘find’ highly isolated and improbable functional sequences amid vast spaces of combinatorial possibilities.” (Stephen C. Meyer, “The Cambrian Information Explosion,” in Debating Design, p. 388 (William A. Dembski and Michael W. Ruse eds., Cambridge University Press, 2004).)
Convergent evolution implies that these rare functional sequences are discovered not just once, but repeatedly. Perhaps a better explanation for the existence of rare functional sequences is intelligent design. Paul Nelson and Jonathan Wells explain why intelligent design is a viable explanation for the repeated appearance of similar gene sequences:
An intelligent cause may reuse or redeploy the same module in different systems, without there necessarily being any material or physical connection between those systems. Even more simply, intelligent causes can generate identical patterns independently. (Paul Nelson and Jonathan Wells, “Homology in Biology,” in Darwinism, Design, and Public Education, pg. 316)
Might convergent genetic evolution actually be a pointer to intelligent design?