Empty Words: Convergent Evolution
“Convergent Evolution” is an attempt
to explain the inexplicable
by Darwinian processes
Darwinians use the phrase “Convergent Evolution” to explain why animals that have very different phylogenies, and thus very different genetic evolutionary trees, have several major features in common.
A Scenario
Let me give an exaggerated story which effectively illustrates the idea of convergent evolution as a supposed connection between humans and fish. According to evolution, humans and fish evolved from a theoretical microscopic organism that lived about 3.7 billion years ago and left in the fossil record a type of carbon molecule produced by living things. After a claimed 3.7 billion years of evolutionary divergence, fish and, eventually, humans evolved, which are both placed at the ends of the branches at the very top of the evolutionary tree.
It was then discovered that humans and fish have several identical bones, even though evolutionists claimed that they diverged along separate evolutionary lines 2.3 billion years ago. Furthermore, their ancestors did not show any evidence of this specific bone in the extensive fossil record of either humans or fish. The only explanation must be that, although human and fish ancestors do not have these bones, humans and fish must have independently evolved these identical bones by convergent evolution in the past few thousand years, because the bones conferred an evolutionary advantage to both the fish and humans.
The research published in Nature this month related an example that closely parallels my illustrative scenario above.
Skeletal convergence in sharks, ichthyosaurs, whales, and tunas
Motani and Shimada analyzed tunas, lamnid sharks, modern whales, and derived ichthyosaurs. These all have numerous traits in common, even though evolutionary consensus agrees that their lineages diverged many millions of years ago. Traits in common include a thunniform body plan.
Diagram showing various water environment styles of movement. Thunniform is the penultimate (the next to the last) movement among unrelated marine animals.
A thunniform body plan is characterized by a compressed peduncle (an elongated stalk of tissue) with a pair of keels (the longitudinal structure along the ventral center line, such as at the bottom of a vessel’s hull), a deeply forked lunate caudal fin (crescent-shaped tail fin), a large fin-span, and a dorsoventrally, near-symmetrical fusiform (torpedo-shaped) body, (a fusiform body is a spindle-like shape, wide in the middle of the body which then tapers at both ends.
The fusiform body plan.
The only option for explaining these similarities by evolution is convergence. The scientists write:
Thunniform vertebrates represent an iconic example of evolutionary convergence in which body plan and swimming style of large cruising marine vertebrates exhibit tuna-like features. Their phylogenetic spectrum is arguably the broadest among evolutionary convergences known in vertebrates.[1]
Evolutionary convergence “is often explained as the result of adaptation to similar ecological niches.”[2] A caveat is that, “Although this claim of evolutionary convergence [discussed by Motani and Shimada] has been studied for a long time …little is known about whether all four clades share any skeletal characteristics.”[3] The analysis of this question by Kelley and Motani located similar skeletal characteristics in all of the animals he looked at which have been interpreted to support convergence as the evolutionary explanation.
Problems with the Explanation
Motani and Shimada presented no scientific evidence for evolutionary convergence, (such as fossil evidence as discussed in my scenario), by the gradual evolution of the traits they analyzed. The structures that Motani and Shimada were evaluating are all hard tissues that preserve comparatively well in the fossil record. This means that intermediate forms should have been found as fossils if they had existed. Their conclusions were based on the belief that the vertebrates they analyzed diverged after millions of years. Consequently, they assume, the traits in living specimens must have emerged by convergent evolution.
Chart presented in the Ryosuke Motani and Kenshu Shimada (2023) research showing the eons-long evolutionary history believed to have produced the genetic divergence of the listed life-forms. Note that no phylogeny is shown that illustrates the gradual evolution from one animal class to another type such as from Synapsida to Mammalia.
Horror Stories
I completed a Google-scholar search and found other claims of evolutionary convergence related to marine animals. One relevant paper assumed that “Terrestrial vertebrates have repeatedly re-adapted to marine life since their ancestors originally left the water over 300 Myr ago.”[4] This study also did not use fossil comparisons, but rather made comparisons of extant (living) marine tetrapod taxa for which dietary patterns can be directly observed to classify their feeding environment. Based on the current evolutionary consensus, they assumed that aquatic animals evolved into terrestrial animals, then returned into the sea and re-evolved into aquatic animals! The most common animal example of this “just-so” story is the whale.
Tale of the Teeth
Motani and Shimada identified skull and tooth morphology patterns that would be expected from a design perspective, which allowed them to survive in an aquatic environment. Since diet is dependent on skull and tooth traits, the researchers estimated their diet by analyzing teeth and jaws. Herbivores, omnivores, and carnivores have drastically different diets, and possess teeth designed specifically to handle their respective food sources. Animals that have vegetarian diets have large, flat teeth for grinding plant matter. Carnivorous diets require teeth geared specifically toward ripping, tearing, and breaking down meat. To do this they also require strong facial muscles. Omnivores have a mix of these teeth types to accommodate both meat and vegetable diets.
The tooth comparison did not provide support for their convergent evolution theory, but only provided details about each animal’s lifestyle and diet. It actually illustrated evidence of design. Without a supportive fossil record, the only “support” for what was observed is the assumed “convergent evolution” explanation.
Summary
“Convergent evolution” is not a scientific explanation. It is a rationalization designed to explain away some of the major problems with the conventional evolutionary theory of divergence into a branching pattern that would be expected from common descent via natural selection. Creationists and Intelligent Design theorists account for the similarities as the result of engineering, using a common design that works. The jaw and teeth structures are thus easily explained as part of the original design of tunas, lamnid sharks, modern whales, and ichthyosaurs, without the improbable and convoluted story that similar traits re-evolved multiple times.
References
[1] Motani, Ryosuke, and Kenshu Shimada. Skeletal convergence in thunniform sharks, ichthyosaurs, whales, and tunas, and its possible ecological links through the marine ecosystem evolution. Nature Scientific Reports, https://www.nature.com/articles/s41598-023-41812-z, October 2023.
[2] Kelley, Neil P., and Ryosuke Motani. Trophic convergence drives morphological convergence in marine tetrapods. Biology Letters 11(1): 20140709, 1 January 2015.
[3] Motani and Shimada, 2023.
[4] Kelley and Motani, 2015.
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.