From ScienceDaily:
Moving one’s body rapidly through water is a key to existence for many species. The Persian carpet flatworm, the cuttlefish and the black ghost knifefish look nothing like each other — their last common ancestor lived 550 million years ago, before the Cambrian period — a new study uses computer simulations, a robotic fish and video footage of real fish to show that all three aquatic creatures have evolved to swim using the same mechanical motion.
These three animals are part of a very diverse group of aquatic animals — both vertebrate and invertebrate — that independently arrived at the same solution of how to use their fins to maximize speed. And, remarkably, this so-called “convergent” evolution happened at least eight times across three different phyla, or animal groups, supporting the belief that necessity played a larger role than chance in developing this trait. The findings could help scientists better understand evolution as well as help pave the way for highly agile underwater vehicles.
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“Chance does play a role in these animals — they don’t all adhere exactly to the optimal number 20 — but there is a point where variability can become deadly, that swimming with the wrong mechanics means you waste energy and won’t survive,” MacIver said. “The ratio of 20 is best.”More.
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Examples of animals evolving similar traits despite the absence of that trait in the last common ancestor, such as the wing and camera-type lens eye in vertebrates and invertebrates, are called cases of convergent evolution. – Rahul Bale et al.
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Here’s the abstract:
Examples of animals evolving similar traits despite the absence of that trait in the last common ancestor, such as the wing and camera-type lens eye in vertebrates and invertebrates, are called cases of convergent evolution. Instances of convergent evolution of locomotory patterns that quantitatively agree with the mechanically optimal solution are very rare. Here, we show that, with respect to a very diverse group of aquatic animals, a mechanically optimal method of swimming with elongated fins has evolved independently at least eight times in both vertebrate and invertebrate swimmers across three different phyla. Specifically, if we take the length of an undulation along an animal’s fin during swimming and divide it by the mean amplitude of undulations along the fin length, the result is consistently around twenty. We call this value the optimal specific wavelength (OSW). We show that the OSW maximizes the force generated by the body, which also maximizes swimming speed. We hypothesize a mechanical basis for this optimality and suggest reasons for its repeated emergence through evolution. Open access – Rahul Bale, Izaak D. Neveln, Amneet Pal Singh Bhalla, Malcolm A. MacIver, Neelesh A. Patankar. Convergent Evolution of Mechanically Optimal Locomotion in Aquatic Invertebrates and Vertebrates. PLOS Biology, 2015; 13 (4): e1002123 DOI: 10.1371/journal.pbio.1002123
So not only did life forms have to solve a special problem of rapid locomotion, different ones had to solve it a number of times, with few if any hints from their ancestry. What are the informational probabilities of that? Wouldn’t the odds against this be greater than against it happening just once?
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