Logic and evolution: making vertebrate eyes (Introduction)

by David Turell @, Thursday, February 16, 2017, 19:59 (858 days ago) @ David Turell

The following illustrates that evolution is incapable of making vertebrate eyes, although complex eyes go back to the Trilobites with crystal bifocal lenses:


"two biologists created a computer simulation, demonstrating, in their view, the incremental evolution of an eye in fewer than 400,000 generations.

"This often-repeated tale sounds impressive at first, but it is not unlike most supposed explanations of the evolution of complex features. It scores high on imagination and flare but low on empirical evidence and thoughtful analysis. It most certainly does not represent a "detailed hypothesis."....In particular, it ignores the details of how a real eye functions and how it forms developmentally. When these issues are examined, the story completely collapses.


" During development, cells divide, migrate, and differentiate into a wide variety of types. Throughout this process, the cells send chemical signals to their neighbors, and these signals cause proteins known as transcription factors (TF) to bind to genes in regulatory regions, which control the corresponding genes' activity. The TFs bind to what are called transcription factor binding sites (TFBS), and the correct binding enables the genes to produce their proteins in the right cells at the right time in the right amount.

"The evolution of additional components in the vertebrate eye requires that this network of intercellular signals, TFs, TFBS, chromatin remodeling, as well as many other details be dramatically altered, so that each developmental stage can progress correctly. For instance, the seemingly simple addition of a marginally focusing lens -- that is to say, a lens that directs slightly more light onto a retina -- requires a host of alterations.


"The challenge to evolution is that, short of completion, most of these changes are disadvantageous. A lens that has not fully evolved through the third step noted above would either scatter light away from the retina or completely block it. Any initial mutations would then be lost, and the process would have to start again from scratch. In the context of fitness terrains, an organism lacking a lens resides near the top of a local peak. The steps required to gain a functional lens correspond to traveling downhill, crossing a vast canyon of visually impaired or blind intermediates, until eventually climbing back up a new peak corresponding to lens-enhanced vision.

" Once an organism has a functional lens, natural selection could then potentially make gradual improvements. However, moving from a reasonably functional lens to one that produces a high-resolution image is rather complex. In particular, the refractive index (i.e., crystalline concentration) has to be adjusted throughout the lens to vary according to a precise mathematical relationship. A gradual decrease from the inside to the outside is needed to prevent spherical aberrations blurring the image.


"Feedback circuitry must be added to allow the lens to automatically refocus on images at different distances.

"The retina has to be completely reengineered to process high-resolution images, including the addition of circuits to enable edge and motion detection.

"The neural networks in the brain have to be rewired to properly interpret the pre-processed high-resolution images from the retina.

"Higher-level brain functions must be enabled to identify different objects, i.e., dangerous ones such as a shark, and properly respond to them.
Until steps 2 through 4 are completed, a high-resolution image would likely prove disadvantageous, since most of the light would be focused on fewer photoreceptors.


"For any species, upgrading to high-resolution vision requires massive reengineering in a single step. Such radical innovation, coordinated to achieve a distant goal, is only possible with intelligent design. "

Comment: Eyes are highly complex, and the interpretive areas in the brain are similarly very complex. As the article points out there can be no intermediate forms, as they would not give any form of satisfactory vision. Only a fully formed system must appear, by saltation, i.e., design. Trilobite eyes appeared de novo with no precursors supporting the saltation theory. Bit by bit evolutionary change will not work.

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