Co-option in Evolution

This is basically a post I made on CARM to an idiot who believed in both front-loading AND special creation, who uses the fact that I could not give a response about co-opting to dodge a dozen questions he could not answer. So I gave him the answer. He, of course, still could not answer the questions because... well, creationism.

Because evolution is real science, there are a lot of papers on this that make interesting reading. Here is a great one from 2008. By the way, all these papers are from the last twenty years. This is a dynamic and on-going area of research. That is the nature of evolutionary science.

Here is the abstract, which I am quoting to highlight that co-option was something Darwin proposed, so the idea is as old as the theory of evolution. Of course, we now have a vast amount of data that confirms it.

Darwin believed that evolution generally occurred through a series of small, gradual changes. This proposal was counter-intuitive to many people because it seemed likely that “transitional” forms would not survive. Darwin, and later Cuènot, recognized that this problem was easily solved if characters that had evolved for one reason changed their function at a later time with little to no concurrent structural modification, at least initially. In other words, traits that had evolved under one set of conditions were co-opted to serve a different function under a second set of conditions. This meant that organisms carried with them in the structures of their genes, proteins, morphological, physiological, and behavioral characters the potential for rapid evolutionary change, so rapid, indeed, that the process looked miraculous and Lamarckian. In this paper, I discuss some of the paradigm examples of co-option, from genes to behavior.

The paper says this, with regards to limbs. 

Overall then, did limbs and lungs evolve as an adaptation to living on land, as was once believed? The answer is No, these characters existed before vertebrates moved onto land, and may have served a variety of functions, including life as an ambush predator, supporting the body while raising the head up and out of the water to breathe air, and maneuvering through vegetation-rich waters. Was the existence of limbs and lungs in aquatic species a critical prerequisite to the quantum leap from an aquatic to a terrestrial existence? The answer to this question is a resounding Yes, without the co-option of these characters vertebrates may never have made that leap: limbs that were once used to maneuver through tangled aquatic habitats, to rest and move along the bottom of shallow estuary, river, and stream margins were co-opted to serve a new function: support and movement on land.

A short article in Nature from 2014 here.

The team took a direct approach to answering this question: test the N. vectensis genes in well-established bilaterian model systems, namely the fruit fly Drosophila melanogaster and the African clawed frog, Xenopus laevis. Despite differences in the genetic sequence, the sea anemone Hox and TALE genes were able to fill in for their Drosophila counterparts in flies lacking those genes, and a mis-expressed N. vectensis gene even turned the fly's antenna into a leg. Likewise, an anemone TALE gene was good enough to activate the expression of several patterning genes in Xenopus embryos. Finally, the researchers included a negative control; TALE genes from the unicellular amoeba Acanthamoeba castellanii weren't able to form a complex with Hox and activate downstream genes. In the authors' words, this work "underlines that the evolution of the TALE partners enabled the interaction network with Hox proteins and hence new functions to emerge during eukaryote evolution."

This paper from 2002 discuses in some detail crystallins; proteins in the lens of the eye. This was also in the first paper. This is a topic that is especially well researched. Just imagine being able to say that about anything in creationism!

Two classes of crystallins, the α and the βγ families, are found in all vertebrate lenses and were probably present in the ancestral vertebrate eye. The common theme uniting the two families of lens-specific crystallins found throughout vertebrate eyes is that proteins involved with cellular stress responses have been co-opted to serve refractive functions in the lens. In this tissue, proteins must remain stable for long periods (i.e., the animal’s lifetime) in an avascular, non-innervated environment that in many animals is exposed to high light levels. It has been speculated that functions involved with cellular stress responses and protein stability may have been pivotal in their original evolutionary recruitment in the lens.

With regards to light sensitive proteins in the eye, we have this paper from 2009:

The first step of photoreception is mediated by light-sensitive transmembrane proteins containing retinal chromophore, generally termed rhodopsins. They have been found in most groups of organisms including archeal prokaryotes (Blanck & Oesterhelt 1987), unicellular eukaryotes (Nagel et al. 2002), fungi (Bieszke et al. 1999) and metazoa. The functions of rhodopsins in these organisms vary from photon-driven ionic pumps in prokaryotes (Blanck & Oesterhelt 1987), sensory molecules in fungi, to a light-gated ion channel in the eyespot of green algae (Spudich et al. 2000; Nagel et al. 2002).

Take a look at figure 1, which gives an excellent graphical representation of the evolutionary process.

The overall message here is that there is a huge amount of evidence for co-option in a wide variety of biological systems, and scientists are doing more and more research, giving us a better and better understanding of it. Every day we know more about co-option in biology.

All of this fits perfectly with evolution, of course. The reason for that is because evolution actually happened.