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Symmetry is very common in nature. It is found wherever mirror images are repeated, such as in the right and left halves of elephants or butterflies, or in the arms of flower petals and starfish that repeat around a central point. It’s even hiding in the structures of little things like proteins and RNA. While asymmetry certainly does exist in nature (like having your heart on one side on your chest or male fiddler crabs having an enlarged claw), symmetrical forms are too common in living things to be random.
Why is symmetry superior? Biologists aren’t sure – there’s no natural selection reason for the prevalence of symmetry in such a variety of life forms and building blocks. Now it looks like a good answer may come from the field of computer science.
on a sheet of paper Published this month in the Proceedings of the National Academy of SciencesThe researchers analyzed thousands of protein complexes and RNA structures, as well as a network of model molecules that control how genes are turned on and off. They found that evolution tends towards symmetry because the instructions for generating symmetry are easier to follow and insert into the genetic code. Symmetry is perhaps the most basic application of the saying “work smarter, not harder”.
“People are often quite surprised that evolution can make these incredible structures, and what we’ve shown is that it’s actually easier than you think,” said Ard Louis, a physicist at the University of Oxford and author of the study.
“It’s like we’ve found a new law of nature,” said Chico Camargo, a lecturer and co-author in computer science at the University of Exeter in England. “That’s beautiful, because it changes how you see the world.”
Louis, Dr. Camargo and colleagues, Iain Johnston, are trying to discover the evolutionary origins of symmetry, Dr. Johnston began his PhD while running simulations to understand how viruses build their protein shells. The resulting structures were highly prone to symmetry and appeared much more frequently than pure randomness would allow.
The researchers were surprised at first, but it made sense—algorithms that produce simple, repetitive patterns are easier to execute and harder to break. Now working at the University of Bergen in Norway, Dr. Johnston likens it to telling someone how to lay a floor: It’s easier to instruct to lay repeating rows of identical square tiles than to explain how to make an intricate mosaic.
Over the next decade, the researchers and their team applied the same concept to key biological components, examining how proteins come together in clusters and how RNA folds.
Dr. “The shapes that appear more often are the simpler ones or the less crazy ones,” Camargo said.
Imagining RNA and proteins as tiny input-output machines executing algorithmic genetic instructions explains the trend towards symmetry in a way that Darwin’s “survival of the fittest” failed to achieve. Because it is easier to code instructions to build simple, symmetrical structures, nature has to choose from a disproportionate number of these simple instruction sets when it comes to natural selection. Dr. Camargo produces disproportionate symmetry due to its simplicity, making evolution a bit like a “sided game with loaded dice”.
While their paper focuses on microscopic structures, the researchers believe this logic extends to larger, more complex organisms. Dr. “It would make a lot of sense if nature could reuse the program to produce one leaf, instead of having a different schedule for each of the 100 leaves around the sunflower,” Johnston said.
While there is still a gap between demonstrating the statistical bias towards microscopic symmetry and explaining the symmetry we see in plants and animals, Gábor Holló, a symmetry biologist at the University of Debrecen in Hungary, says he is excited by the results of the new paper. . Not included in the study, Dr. “Explaining how such a natural and such a universal trait emerged in evolution, in nature, that’s one thing,” Holló said.
Similarly, Luís Seoane, a complex systems researcher at the Centro Nacional de Biotecnologia in Spain, who was not involved in the study, praised the work as “as legal as it can be”.
Dr. “There’s an ongoing battle between simplicity and complexity, and we live right on the edge of it,” said Seoane. The universe is leaning toward ever-increasing randomness, he added, but these simple, symmetrical building blocks help make sense of that complexity.
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