Posted by: davidlarkin | February 28, 2009

Evolution “Invents” a New Photoreceptor in Humans

In the December 24, 2008 issue of The New Republic, Oren Harman reviewed a book on biological clocks, Rhythms of Life: The Biological Clocks that Control the Daily Lives of Every Living Thing by Russell G. Foster and Leon Kreitzman, Yale University Press (2005). Link to The New Republic book review.

In the review, Harman explains that scientists have discovered that the internal biological clocks in animal organisms are synchronized to the outside world by cues from the environment. Syncronization is necessary for the internal biological clock to operate in the world and be useful to the organism in survival. The process is called “entrainment.” Harmon writes:

. . . while cues like temperature, food availability, humidity and even social contact can act as triggers, light is nature’s greatest entrainer of all.

This makes good evolutionary sense. Light is the most stable of these cues, and it can be used not only to signal dawn and dusk, but also, since the amount of light falling on the Earth varies precisely with latitude and season, to calculate the time of year.

In his discussion of how light “entrains” an organism’s biological clock, not surprisingly, Harman offers no explanation of how light in the environment causally effects evolution to bring about this new biological feature. Of course, it cannot because current evolutionary theory relies on microbiological change unconnected to the environment. That new mammalian receptor would have to evolve through a pathway of naturally selected random mutations of DNA uninfluenced by the light of day or the dark of night, and then be naturally selected once the pathway randomly produced the final functioning new receptor.

Presumably, historical evolutionary reptilian precursors to mammals without the new receptor would have trouble getting to sleep and waking up with no biological clock, but apparently that would not prevent survival until the receptor appeared in the evolutionary advanced human species we are. Apparently, then, the mammal with the new receptor would be be more fit for survival, for example, now able to follow the maxim: “Early to bed, early to rise, makes a man healthy, wealthy and wise.” Accordingly, he and she would dominate in the battle of the selfish genes, and the inferior time-confused genetically-older semi-reptilian brethren, rising too late or too early, would become extinct.

The alternative to development in accordance with the gradulism premise of Darwinism, would be a giant random genetic leap from reptile without the new class of receptors to a mammal with it. The massive genetic mutation necessary for the information in that leap is likely highly mathematically improbable. The gene that expresses the protein that connects the inside of muscle cells to the outside, running through the cell membrane, for example, has 2.5 million base pairs in a specific order. What precise genetic information would be necessary for a new photoreceptor containing multiple proteins?

Harman writes:

“Light has been such an important entrainer that evolution has even “invented” in mammals a whole new class of photoreceptors, different from the rods and cones used for vision, in order to bring it safely to the SCN in the brain. [“SCN” is the suprachiasmatic nuclei of 20,000 neurons in the brain now believed to be the neural center of biological clocks] The surprise existence of such receptors, discovered in Russell’s own lab six years ago, made it clear that even diseased eyes need to be kept intact in order to allow them to perform their circadian functions. Blind people, with no working rods and cones, still need their eyes for waking and sleeping.”

Thus, with great unspoken faith in evolution as an explanation, even recognizing the miraculous nature of this biological development in humans by his use of the language of creation and design, though he uses quotation marks to let you know that he is only kidding, Harman writes about evolution “inventing” this new receptor, with no thought of just how an empty-headed, dice-rolling machine of “evolution” might have done done that.

This is another example of the underlying evolutionary principle of expedient use and disuse of probability estimates in light of scientifically established historical time. For a scholarly discussion of the probability problem in micro-evolution of the species, see Stephen Meyer’s paper from the Proceedings of the Biological Society of Washington, The origin of biological information and the higher taxonomic categories. If it could have happened by chance, it did, regardless of the probability in light of time available or the lack of evidence in natural history or the laboratory. That is great faith.

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Responses

  1. New? I’d suspect that entrainment to the light/dark cycle in nature is one of the oldest capabilities of all living things including unicellular ones. Much, much older than vision. The only thing “new” about the “new class of photoreceptors” is that they are newly discovered. We learned about rods and cones in middle school; light sensitive retinal ganglion cells hadn’t been discovered yet.

    • Certainly the photoreceptor was newly discovered, a trite point, but the point the author of the review was making was that it was a new complex protein molecule suddenly appearing in the mammalian species, “invented by evolution.” There are non-sight-related photoreceptor molecules in other classes of the animal kingdom, like fish, for example, that may be used in entrainment. The mammalian photoreceptor molecule itself is a melanin/ospirin protein. Ospirins are types of proteins sensitive to light that exist in rods and cones in birds, fishes and mammals, i.e., animals with eyes. The “new” photoreceptor was new in natural history. My point was that the it takes great faith to believe that this new complex protein was the result of a random modification of genetic structure in DNA that solves a survival problem for the mammal, regardless of whether there were other photoreceptor proteins in other animals that served non-sight functions. How did mammals survive prior to the just right random mutation to a complex set of genetic code that produced a new melanin/ospirin protein molecule that allowed the mammal to survive and exist as mammals?

  2. That’s a fascinating review (at http://www.tnr.com/story_print.html?id=f2362238-e0a0-4917-a56c-4d59bc456462 ) — makes one want to read the book. The knowledge gained in the 20th century is extensive and remarkable about the “common mechanisms–built of different concrete parts–in circadian systems and photoperiodic effects everywhere,” as Pittendrigh put it mid-century. As Harman says, figuring out the ancient basic workings of all living beings’ internal rhythms “has been one of the most impressive journeys in the recent history of science. Showing that, since many of the genes and proteins that tell time are similar in mice and flies, there must have been an ancestral clock for insects and mammals going back seven hundred million years–and a much, much earlier one for bacteria–is an extraordinary accomplishment.”

    Good as the review is, its author and not the book must be blamed for causing the misconception that melanopsin-containing ganglion cells in the mammalian retina are “new”. Harman uses the word “invented” strangely also in his book title “The Man Who Invented the Chromosome”. There, in the introduction, he blames the use of the word on the Honorable Dame Miriam Rothschild. I do wish he wouldn’t perpetuate it.

    So, no, a new complex protein molecule didn’t “suddenly appear” in mammals!


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