"Convergent Evolution" Widespread at All Scales in Ocean
A study of marine tetrapods that “evolved” for ocean life shows “convergent evolution” rampant at all scales over “hundreds of millions of years.”
What do penguins, mosasaurs, sea lions, sea turtles, and whales have in common? For one, they are tetrapods (4-legged creatures) that live in the ocean. For another (according to evolutionary theory), they began as land animals. A new study published in Science Magazine shows, however, that they (and many others) share such similar features that the only way to explain it is by “convergent evolution.” This is the notion that unrelated creatures evolved the same solutions to environmental problems independently. But is this a scientific explanation, or a phrase looking for meaning?
Sascha Vignieti explains in a short review in Science Magazine how the environment becomes the “selector” in convergent natural selection:
Over biological history, several different groups of vertebrate tetrapods have reinvaded the marine environment. Although these groups are widely distributed among reptiles, mammals, amphibians, and birds, the shapes they have evolved are remarkably similar. Kelley and Pyenson review the literature on marine vertebrate groups over time and describe the innovations that facilitated the evolution of these marine forms, the environmental conditions that selected for such convergence of form, and the threats they face from future environment change.
The “environmental threats” angle (by humans, presumably) is just a footnote in the main point by Neil P. Kelley and Nicholas D. Pyenson’s paper, “Evolutionary innovation and ecology in marine tetrapods from the Triassic to the Anthropocene” (for Anthropocene, see 4/11/15). Noting the similarity of shapes, flippers, and other adaptations to aquatic life, they call on the power of “convergent evolution” repeatedly to explain commonalities found from the molecular level to the whole animal. A few examples:
- Fig. 2 Convergent morphology in marine tetrapods. Similar anatomy evolved among lineages that independently adopted marine lifestyles.
- [List of 9 animals] showing anatomical convergence reflecting limb streamlining.
- [Section heading] Convergent evolution from molecules to morphology
- Marine tetrapods provide canonical illustrations of evolutionary convergence (Fig. 2), widely regarded as repeated solutions to problems imposed by physical contrasts between land and water.
- Functional trade-offs can ultimately drive specialization and steer evolutionary convergence, as with repeated loss of flight among seabirds specialized for aquatic locomotion. In vivo studies of feeding performance provide similar insight into functional trade-offs and specialization, which shaped convergence in marine tetrapod feeding systems.
- Fossil anatomy reveals the evolution of countercurrent heat exchange in penguins, convergent with similar systems in marine mammals [e.g., whales, walruses].
- The scope of recent studies of convergent evolution extends beyond morphology to include molecular physiology, metabolism and thermoregulation, and life history.
- Genomic investigations have revealed convergent genetic origins of important innovations, such as sex determination mechanisms, myoglobin adaptations facilitating deep diving, and echolocation.
- Stable isotopes from fossils elucidate parallel histories of habitat shift in early cetaceans and sirenians and convergent evolution of endothermy in Mesozoic marine reptiles.
- Recent breakthroughs in fossil pigment reconstruction have resolved structural and pigment adaptations in fossil seabird feathers and have revealed widespread dark coloration in fossil marine reptiles, possibly for temperature regulation or ultraviolet light protection.
- Exceptionally preserved fossils document convergent reproductive adaptations in marine reptiles. Recently discovered early ichthyosaur fossils extend the history of viviparity [giving birth to live young] in this group back to the Early Triassic and indicate that viviparity evolved in terrestrial forerunners as an enabling factor for, rather than an adaptive response to, aquatic life.
- Fossils suggest that some marine reptiles converged upon K-selected life histories [i.e., stable populations] observed among marine mammals.
- Aquatic birth evolved early in cetacean [whale] and sirenian [seal] evolution, but these transitions are so far only partly constrained by fossils.
- These episodes of replacement between lineages are mirrored by iterative patterns within lineages. For example, evolution of herbivory and durophagy (feeding on hard-shelled prey) drove repeated convergent feeding morphologies in living and fossil sea turtles.
It’s everywhere, in other words: shape, coloration, birth patterns, warm-bloodedness, feeding habits, echolocation, thermal regulation, metabolism, genes—you name it, “convergent evolution” did it. But how does convergent evolution work? In the section “Causes and consequences of convergence, innovation, and radiation,” Kelley and Pyenson offer ideas:
In addition to external drivers, convergent evolution is shaped by the underlying genetic and developmental pathways that give rise to convergent structures. Thus, repeated evolution of hydrodynamic limbs and axial modifications likely exploited parallel developmental mechanisms. Such shared pathways may extend to the level of gene regulation linking genomic and phenotypic convergence and innovation. Recent work on marine mammal genomic convergence has questioned the prevalence of such linkages; however, more work is needed to evaluate potential scaling of convergence from gene to phenotype.
But saying “convergent evolution is shaped by the underlying genetic and developmental pathways that give rise to convergent structures” is no more informative than saying, “A mystery is shaped by the underlying genetic and developmental pathways that give rise to mysteries.” In their view, complex “innovations” (like echolocation) appear like magic:
Innovations facilitate and constrain downstream evolution, as illustrated in the discrete pathways from drag-based to lift-based swimming in limb- and tail-propelled aquatic mammals. Likewise, independent innovation of aquatic birth in multiple marine reptile and marine mammal lineages removed the constraints of terrestrial locomotion, enabling limb and skeletal modification to increase swimming performance, as well as gigantism in some clades. Convergent evolutionary pathways [e.g., the emergence of tail-driven locomotion in ichthyosaurs, mosasaurs, and whales (Fig. 2A)] might follow similar tempos across groups, but this hypothesis awaits further testing.
The authors do not point to any actual transitions documented in fossils between land animals without the innovations to well-adapted marine creatures with them. Their only reference to “discrete pathways from drag-based to lift-based swimming” is to a 1996 paper by F. E. Fish, who merely assumed that transitions had to occur by evolution. He saw that land animals and semi-aquatic animals experience drag, as opposed to highly-adapted marine mammals like whales and dolphins whose tail flukes with an up-and-down motion are more efficient. That transition alone would have required major anatomical changes to the skeleton, musculature and other systems. What possible evidence is there for a statement like, “Independent innovation…removed the constraints of terrestrial locomotion, enabling limb and skeletal modification to increase swimming performance….”? How did innovation happen, let alone independent innovation multiple times? They merely assume innovation happened, with no explanation other than using its handwaving synonym, “emergence.”
Within their category of “innovations” that “emerged” somehow, there are highly-complex systems of interdependent parts:
Diversification can be triggered by innovations that occur well after initial invasions. For example, echolocation and baleen—two key innovations that evolved tens of millions of years after whales first entered the oceans—mark the emergence of crown cetaceans.
The devil, though, is in the details. Echolocation requires a number of specialized adaptations, as observed in dolphins: (1) a sound production mechanism (the phonic lips, very different from vocal cords); (2) a means of reflecting the sounds outward (performed by a modified skull); (3) a means for focusing the sound (the melon); (4) an antenna for receiving the echoes (performed by the jaw and teeth); (5) a means for channeling the echos into the inner ear; and perhaps the most challenging feature, (6) a means for interpreting the signals and responding to them. Dolphin echolocation is more advanced than any man-made sonar. Dolphins can locate a BB in a swimming pool blindfolded, can find fish 6″ under the sand, and can tell the difference between a golf ball and a ping-pong ball by density alone.
Counter-current heat exchangers (CCHE), referred to in the paper, are another example of complex systems. These would have required multiple “innovations” from land ancestors: (1) dorsal fins and tail flukes instead of legs; (2) absence of blubber is the fin and fluke; (2) vein networks close to the skin of the dorsal fin and tail fluke to shed excess heat; (3) rete mirabile (“miraculous nets”) of arteries and veins where blood moves in opposite directions, so that the cooled veins can absorb heat from the arteries; (4) locating the retes where they are needed. All these elements must exist together, simultaneously, for the heat exchange to work. This is especially notable in the case of the reproductive organs of whales. Unlike land mammals, the male cetacean has testes inside the body, wedged between two huge swimming muscles that get hot during fast swimming. Yet the testes must be cooler than body temperature to produce sperm. It’s like trying to run a refrigerator between two heat engines. The CCHE is so effective in whales and dolphins, it actually cools the testes even more during hard swimming. In the female, the CCHE keeps the developing fetus from overheating.
A little reflection shows the “emergence” of the CCHE presenting a severe challenge for Darwinian theory. Evolution relies on reproduction. Without the CCHE already present and functioning, the male can’t produce sperm. The female, likewise, cannot keep the fetus from dying of overheating. This would spell extinction for the proto-whale in one generation, before it even gets into deep water. Ocean water itself (“the environment”) cannot select something that isn’t there. Yet how could blind mutations bring about all the elements of the CCHE together at the same time? And without echolocation, how could the whale or dolphin eat?
These challenges are completely ignored by Kelley and Pyenson. To them, “innovation” just occurs. How? By “emergence.” Yet the Smithsonian Newsdesk thinks their ideas are “seriously amazing.”
For more than 250 million years, four-limbed land animals known as tetrapods have repeatedly conquered the Earth’s oceans. These creatures—such as plesiosaurs, penguins and sea turtles—descended from separate groups of terrestrial vertebrates that convergently evolved to thrive in aquatic environments.
In a new scientific review, a team of Smithsonian scientists synthesized decades of scientific discoveries to illuminate the common and unique patterns driving the extraordinary transitions that whales, dolphins, seals and other species underwent as they moved from land to sea.
This article, too, is infatuated with the phrase “convergent evolution,” using it 8 times. Some may question how illuminating it is to chalk the extraordinary transitions to a vacuous idea that assumes what it needs to prove.
How can we put a stop to the Darwin Party flimflam show, with its magical mystery tour featuring “convergence” and “emergence” and “innovation” miracles? How can we stop the blind leading the blind by blind processes? Here’s a way you can get involved. Illustra Media’s latest documentary, Living Waters, will make a powerful case against evolution by specifically rebutting “convergent evolution” and by demonstrating the amazing complexity of the systems described above—and more. It’s due out in June or July. Watch the trailer here, and prepare to be amazed! After Metamorphosis: The Beauty and Design of Butterflies, and Flight: The Genius of Birds, this third documentary in the Design of Life series, employing spectacular photography, cutting-edge science, dramatic animation, interesting interviews with scientists and great music accompanying a winsome presentation, will be one to share with everyone you know.
Expensive high-quality productions like this are made possible by an army of people who support the work by buying the films and donating to Illustra. Join Illustra’s Facebook page, and use your social media network to get the word out. Consider being a regular donor. Buy copies at Go2RPI.com and give them to influential people and friends. And if you’re a praying person, they could use a lot of prayer right now as all the elements of the film—sound, graphics, animations, narration, music, packaging, and more—are being assembled right now.