Blinking is a Big Problem for Evolution
New Research Supports Creation,
Not Evolution
Blinking is often assumed to be a helpful, simple reflex, but not a very important one. However, in reality, it is not only a very complex system, but also a very important reflex for vision.
by Jerry Bergman, PhD
Blinking is often taken for granted and rarely noticed because it is controlled by the autonomic nervous system. The average person blinks every 4 to 6 seconds, which is between 14,400 and 19,200 times daily.[1] Although we can intentionally blink, or inhibit blinking, as in the child’s game of ‘stare down’, blinking is automatic and frequently occurs without conscious awareness, as does breathing. As one report opined,
Blinking is crucial for the eye. It’s how animals clean their eyes, protect them, and even communicate. But how and why did blinking originate [evolve]? Researchers at the Georgia Institute of Technology, Seton Hill University, and Pennsylvania State University studied the mudskipper, an amphibious fish that spends most of its day on land, to better understand why blinking is a fundamental behavior for life on land.[2]
Inhibiting blinking takes practice, and our ability to do so varies greatly, such as is experienced when posing for a group picture to insure that no person will be in the photograph with their eyes closed. We blink spontaneously, about 10 to 15 times a minute, both to moisten and oxygenate the corneas.[3] We also blink reflexively to protect our eyes from potential damage that could be caused by external objects, such as flying insects and unruly hair.
Biologically, we blink to moisten the eye, but not according to purely mechanically predictable intervals between blinks. Instead it varies, depending on the humidity, wind, and other physical factors. The thin-film fluid layer on the surface of the cornea allows the transfer of oxygen from the air to the corneal epithelium, which is not vascularized. For this reason, the blinking system is critical for eyesight. Without it, blindness would result.
Each blink lasts between 100–150 milliseconds.[4] During this time in humans it obstructs all vision and attenuates light levels reaching the retina close to 100-fold. In all mammals blinking operates as a set, thus both eyes are closed simultaneously for spontaneous blinks. By blinking one eye at a time, vision is never completely disrupted, which is what birds do. Conscious blinking can blink one eye only, a process called winking.
The complexity of blinking, which involves the brain, the nervous system and several muscles, indicates that something could go wrong, producing pathology.[5] In general, the more complex a structure, the more that will go wrong. Furthermore, the more complex a structure in general, the more difficult it is to explain by evolution.
Ed. note: For more on the problems the brain must solve to maintain a steady visual reference during a blink, see “The brain is faster than the blink of an eye” (26 July 2005), and “Learn your body toolkit: the eye trick” (25 Jan 2017).
New Attempts to Explain the Evolution of Blinking
The long-term goal of evolution is to explain all human anatomical and physiological processes by evolution, even those that are less complex and less important. A new paper on the topic in PNAS by Aiello et al. (24 April 2023) admits that scientists have no evidence for an evolutionary origin of blinking. That is because
blinking is seen in nearly all living tetrapods and absent in other extant sarcopterygian lineages suggesting that it might have arisen during the water-to-land transition. Unfortunately, our understanding of the origin of blinking has been limited by a lack of known anatomical correlates of the behavior in the fossil record and a paucity of comparative functional studies.[6]
Mudskipper from India. Credit: Rajesh mpt, Creative Commons.
To understand how and why blinking evolved, the authors experimented on mudskippers, a shallow-water fish with eyes that protrude above the surface. Mudskippers spend much of their time out of water. Having evolved from fish that live their entire lifespan in water, they reasoned, mudskippers must have convergently evolved blinking when they began to crawl on land, to fulfill the same functions blinking achieves in tetrapods.
The Research: No Evolution
To study mudskippers, the researchers used microcomputed tomography and histology to analyze two mudskipper species. They then compared the results to the fully aquatic round goby fish. Analysis of the gross anatomy and epithelial microstructure determined that “mudskippers have not evolved novel musculature or glands to blink.” Rather, the mudskipper blink design is not similar to fish, as expected by evolution, but basically the same as tetrapods! Its blinking functions are also the same as in tetrapods: moistening the eye while on land, protecting the eye from injury caused by dust or other objects, and cleaning the eye of debris.
The researchers found that the mudskipper possesses a blinking mechanism typical of land tetrapods that is modified only slightly for the fish’s semi-aquatic environment. They found no evidence of its evolution, so they concluded that it had evolved convergently to appear almost identical to the blinking mechanism and design of land-dwelling tetrapods and humans as well.
One difference, however, was found. In the high-evaporation conditions that mudskippers inhabit, they blink more often to wet the eye and protect it from physical insult. Furthermore, a single mudskipper blink can completely clean the cornea of all particulates. They concluded that
eye retraction in concert with a passive occlusal membrane can achieve functions associated with life on land. Osteological correlates of eye retraction are present in the earliest limbed vertebrates, suggesting blinking capability. In both mudskippers and tetrapods, therefore, the origin of this multifunctional innovation is likely explained by selection for increasingly terrestrial lifestyles.[7]
Speculating About the Lack of Evidence for Evolution
Further adding to their evolutionary speculations, the authors presented the following rationale in an attempt to explain away the lack of evidence for the evolution of blinking.
Approximately 375 mya [million years ago], stem-group tetrapods transitioned from life in the water to life on land. This transition involved a suite of anatomical transformations, including modifications to the feeding, locomotor, and sensory systems. Blinking [involves]… one or more membranes that transiently occlude the eye, occurs in all major crown group tetrapod lineages and is absent in closely related, aquatic lineages (i.e., coelacanth and lungfish). Its origin, therefore, might have coincided with the water-to-land transition. However, the lack of fossilization of associated morphologies (e.g., eyelids and lacrimal glands) and a lack of comparative functional analyses limit hypotheses of how and why blinking first evolved. Several other lineages of fishes have evolved to live at the water’s edge. Analyses of these groups might reveal both the anatomy required to perform a blink and the selective pressures that lead to the origin of this behavior.[8]
The goal of their research was to analyze the morphological basis of blinking and “how and why blinking originated in these fishes [which] might help to clarify the biology of early tetrapods and their transition to life on land.”[9]
Spin Doctoring
So the research gave no evidence for the evolution of blinking. The press release at Georgia Tech, despite the lack of evidence, put a positive spin on it, touting “understanding” as a fruit of the evolutionary research. One headline read: “Mudskippers could be key to understanding evolution of blinking.”[10] It spun the empty evidence all the way up to implications for human evolution, claiming,
Although mudskippers are distantly related to tetrapods, the group that includes humans and other four-limbed vertebrates, researchers believed studying the fish could unlock how blinking evolved as these animals began to move on land.[11]
Summary
What the mudskipper research found was not evidence for evolution, but clear evidence of design in the mudskipper. The mudskipper is a mosaic just as is the Archaeopteryx and the duck-billed platypus. Archaeopteryx has clear dinosaur and bird features, and the duck-billed platypus has features utilized in birds, mammals, and fish. As admitted by an assistant professor at Penn State, Tom Stewart, a co-author of the paper, “These results help us understand our own biology and raise a whole set of new questions about the variety of blinking behaviors we see in living species.”[12]
References
[1] How many times do you blink a day? https://www.utaheyecenters.com/2022/07/15/, 2022.
[2] Georgia Institute of Technology. “Mudskippers could be the key to understanding the evolution of blinking.” 24 April 2023, https://research.gatech.edu/mudskippers-could-be-key-understanding-evolution-blinking
[3] Burr, David. Vision: In the Blink of an Eye. Current Biology 15(14): R554-R556, 26 July 2005.
[4] Burr, 2005.
[5] Medarametla, S., et al. A Curious Case of Excessive Winking. Movement Disorders in Clinical Practice 8(6): 947–949, 29 May 2021.
[6] Aiello, Brett R., et al. The origin of blinking in both mudskippers and tetrapods is linked to life on land. Proceedings of the National Academy of Sciences 120(18): e2220404120; https://doi.org/10.1073/pnas.222040412, 24 April 2023.
[7] Aiello, et al., 2023.
[8] Aiello, et al., 2023; bold added.
[9] Aiello, et al., 2023.
[10] Georgia Tech, 2023.
[11] Georgia Tech, 2023; bold added.
[12] Georgia Tech, 2023; italics added.
Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,300 publications in 12 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,800 college libraries in 27 countries. So far over 80,000 copies of the 60 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.