A new article in the journal Trends in Genetics bears an intriguing title: “The evolutionary diversity of insect retinal mosaics: common design principles and emerging molecular logic.” The mention of “common design principles” doesn’t mean that the authors advocate intelligent design, but their research unwittingly bears on the subject.
They write about patterns, or mosaics, of light-receptor cells in insect eye retinas that are found repeatedly in widely diverse types of insects. These features, they say, are built upon “common design principles,” meaning that they are highly similar despite appearing in independent lineages. As the paper reports:
Independent evolution has resulted in a vast diversity of eyes. Despite the lack of a common Bauplan or ancestral structure, similar developmental strategies are used.
For example, the mosaic of retinal cells in honeybees is very similar to those in fruit flies, despite their being evolutionarily distant:
Characterization of the honeybee Rhodopsin genes revealed striking similarities with the stochastic retinal mosaic of Drosophila, despite considerable differences in ommatidial organization. … Fascinatingly, the overall occurrence of UV versus Blue R7-like cells is approximately 68:32 and, therefore, strikingly similar to the yR7:pR7 ratio in Drosophila (65:35).
The paper gives other examples:
The data from more distantly related insects reviewed here show that some stochastic mosaics look surprisingly similar (honeybee workers, butterflies, and locusts), raising the possibility that patterning via factors similar to Spineless could be conserved.
Spineless is an important developmental gene in insects that is involved in the formation of the antennae, legs, and also, the mosaic of retinal cells that allow insect color vision.
They suggest that the reason these similarities exist is because of “conserved” genetics — i.e., due to inheritance of the same genes from a common ancestor. But remember what they said at the beginning of the paper? They wrote: “Despite the lack of a common Bauplan or ancestral structure, similar developmental strategies are used.” In other word, these are highly diverse types of insect eyes, yet they use common patterns of retinal cells.
The options for explaining these similarities are common ancestry, convergent evolution, and common design. The authors appeal to common ancestry, but given the highly diverse nature of insect eyes, they call the similarities of retinal cell mosaic patterns “surprising” and “fascinating.” They clearly do not want to appeal to convergent evolution because that is so unlikely. We discuss this problem for evolutionary biologists in Discovering Intelligent Design:
It’s difficult enough to evolve a complex structure once. But the odds of evolving a similar feature multiple times, independently, in different lineages, are very low.
Richard Dawkins acknowledges this point, stating “it is vanishingly improbable that exactly the same evolutionary pathway should ever be travelled twice.” Yet he admits there are “numerous examples… in which independent lines of evolution appear to have converged, from very different starting points, on what looks very like the same endpoint.”
Rather than admitting that convergent evolution provides a challenge to Darwinian claims, Dawkins simply believes “[i]t is all the more striking a testimony to the power of natural selection.”
This underscores a dilemma faced by many evolutionary biologists. They find similar complex features in widely different organisms — something that was unexpected under common ancestry, yet that are also hard to explain via convergent evolution. What’s left? How about common design? After all, a prima facie examination of these cell patterns in diverse types of insects reveals, in their own words, “common design principles.” Why can’t “common design principles” potentially indicate “common intelligent design principles”?
You can learn more about how “convergent evolution” undermines the case for common ancestry, instead giving evidence of ID, in our curriculum and new online supplement, Discovering Intelligent Design.