Similar Strokes

Physics drove the convergent evolution of swimming in 22 unrelated marine species, a study suggests.

By Jenny Rood | April 29, 2015


A diverse group of long-finned marine vertebrates and invertebrates that last shared a common ancestor 550 million years ago use the same fin motion to swim with maximal speed in a rare example of a mechanical explanation for convergent evolution, according to a study published today (April 28) in PLOS Biology.

Flatworms, cuttlefish, rays, and triggerfish are among the 1,000 species that belong to a group known as the median/paired fin swimmers. These animals move by rippling a fin that runs the length of their body. When researchers from Northwestern University measured the height of the ripples and the distance between them in videos of 22 unrelated species from three different phyla, they found that the undulations were consistently 20 times as long as they were tall in each animal. By mapping the species on an evolutionary tree, the scientists determined that the motion likely evolved independently eight different times in this group of animals.

To explain why flatworms and rays arrived at the same swimming stroke, a process known as convergent evolution, the scientists tested a variety of ripple length-to-height ratios in a computer model and with a robotic knifefish. In these systems, the researchers found that the 20-to-1 ratio provided the maximum amount of force to propel the animal forward. “We have quantified how an unusual group of swimming animals optimizes force and, therefore, speed,” study coauthor Malcolm MacIver said in a statement.

“Physics seems to have overwhelmed chance in the evolution of these creatures,” study coauthor Neelesh Patankar told The Washington Post. The researchers plan to investigate if other median/paired fin swimmers also use the same ratio to study how physical constraints might influence convergent evolution.


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Avatar of: Paul Stein

Paul Stein

Posts: 237

April 30, 2015

Neelesh Patankar needs to relearn evolution.  Physics WORKED WITH chance in the evolution of these creatures.  The better the physics, the better the survival.

Avatar of: James V. Kohl

James V. Kohl

Posts: 508

April 30, 2015

The biophysically constrained chemistry of nutrient-dependent RNA-mediated amino acid substitutions and protein folding stablizes the organized genomes of species from microbes to man via fixation of the substitutions in the context of their physiology of reproduction.

That fact defies attempts to explain the evolution of these creatures, since they have obviously ecologically adapted to ecological variation in their sources of nutrition, which links metabolic networks to genetic networks and biodiversity in all species.

Claims about evolution can also be placed into the context of the re-evolved bacterial flagellum, which occured over-the-weekend -- as reported here on February 26, 2015 as: Strong selective pressure can lead to rapid and reproducible evolution in bacteria.  What's needed is some consistency in the reporting of claims that try to link physics, chemistry, and conserved molecular mechanisms of protein biosynthesis and degradation. What should not be tolerated by serious scientists is the claims theorists who seem to think that morphology automagically evolved "...independently eight different times in this group of animals."

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