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Awe at Echolocation? Nah, Convergence Again


Thomas Kuhn described normal science as a puzzle-solving project, in which members of the guild don’t question the picture they imagine on the box top (the paradigm). So focused are they on making the pieces fit, they could be failing to appreciate the wonders coming to light in the picture itself. You can see an example of this in two papers about echolocation; a discussion of the second of these will follow tomorrow. 

Think of the awe any sensitive person, even a scientist, should feel as he thinks about biosonar! Imagine the ability to bounce sound off objects in the dark and gain precise information about shapes, textures, and motions. Bats do it. Whales do it. Captain Dave Anderson, who leads whale-watching tours in California, said that a dolphin can tell the difference between a golf ball and a ping-pong ball by sound alone (Illustra Media, Living Waters). That’s not just echolocation. It is “indistinguishable from magic,” in Arthur C. Clarke’s famous comment about sufficiently advanced technology. Illustra’s animation of dolphin sonar reveals numerous complex parts working together to make this possible. Artificial sonar doesn’t come close.

Out of Focus

How does echolocation work? Shouldn’t that be a focus in science? It is for some scientists, who eagerly learn all they can about sonar in toothed whales and bats for the sheer pleasure of understanding a complex biological system that works superbly well. It is, too, for some engineers, who explore design principles in biological sonar that might have applications for human technology. But for many evolutionary biologists, there seems to be an obsession with homology. Some Darwinists will strain over the smallest details, down to single amino acids, to force uncooperative puzzle pieces together that might show how bats are related to whales. Do people on a whale-watching boat care about that? Should they?

In Science Advances, a team of ten evolutionary biologists from Germany announce finding “Molecular parallelism in fast-twitch muscle proteins in echolocating mammals.” You feel their passion for the puzzle in the opening sentence: “Detecting associations between genomic changes and phenotypic differences is fundamental to understanding how phenotypes evolved.” From there, they dive into the nitty-gritty details amino acids that might hint at evolutionary relationships:

By systematically screening for parallel amino acid substitutions, we detected known as well as novel cases (Strc, Tecta, and Cabp2) of parallelism between echolocating bats and toothed whales in proteins that could contribute to high-frequency hearing adaptations. Our screen also showed that echolocating mammals exhibit an unusually high number of parallel substitutions in fast-twitch muscle fiber proteins. Both echolocating bats and toothed whales produce an extremely rapid call rate when homing in on their prey, which was shown in bats to be powered by specialized superfast muscles. We show that these genes with parallel substitutions (Casq1, Atp2a1, Myh2, and Myl1) are expressed in the superfast sound-producing muscle of bats. Furthermore, we found that the calcium storage protein calsequestrin 1 of the little brown bat and the bottlenose dolphin functionally converged in its ability to form calcium-sequestering polymers at lower calcium concentrations, which may contribute to rapid calcium transients required for superfast muscle physiology. The proteins that our genomic screen detected could be involved in the convergent evolution of vocalization in echolocating mammals by potentially contributing to both rapid Ca2+ transients and increased shortening velocities in superfast muscles. [Emphasis added.]

Hammer Seeks Nail

Well! So much for appreciating “an extremely rapid call rate” or “superfast muscles.” This team wants to see homology. It has a Darwin-brand hammer and sees everything as a nail. In order to preserve common ancestry, they are willing to find convergent evolution in function, even when the molecular homology fails.

An important aspect to understanding how nature’s phenotypic diversity evolved is to detect the genomic differences that are associated with phenotypic differences. Despite numerous sequenced genomes, detecting such associations remains a challenge. Convergent evolution, which refers to the repeated evolution of similar phenotypes in independent lineages, offers a paradigm to computationally screen genomes for molecular changes that evolved in parallel in these lineages and thus could be involved in the phenotypic difference.

The e-word, evolution, saturates this paper. Molecular evolution. Parallel evolution. Neutral evolution. Evolutionary tinkering. Whatever it takes, they are going to keep the Darwin puzzle pieces together, even when homology is not evident in the genes. Withering on the lab counter, meanwhile, is awe for the wonder of echolocation.

There is a brief moment of wonder, but it quickly is swallowed up by evolution:

Superfast muscles consist of specialized fibers capable of contracting and relaxing at a rate that is an order of magnitude higher compared to the fastest locomotor muscles. To achieve this extraordinarily high rate, superfast muscles have evolved a number of key adaptations….

Oddly, the only kind of natural selection they mention is “purifying selection.” Also called negative selection, purifying selection refers to the removal of deleterious mutations. You’ll never build a sonar system that way. To them, it’s OK. They already know it evolved. “Evolution is a fact, fact, FACT!”, as Michael Ruse put it, remember?

Photo credit: Dolphins, by werdepate, via Pixabay.