Life’s preference for symmetry is like ‘a new law of nature’
Symmetry runs rampant in nature. It's present wherever mirror images are repeated, like in the right and left halves of elephants or butterflies, or in the repeating patterns of flower petals and starfish arms around a central point. It's even hiding in the structures of tiny things like proteins and RNA. While asymmetry certainly exists in nature (like how your heart is off to one side in your chest, or how male fiddler crabs have one enlarged claw), symmetrical forms crop up too often in living things to just be random.
Why does symmetry reign supreme? Biologists aren't sure — there's no reason based in natural selection for symmetry's prevalence in such varied forms of life and their building blocks. Now it seems like a good answer could come from the field of computer science.
In a paper published this month in Proceedings of the National Academy of Sciences, researchers analyzed thousands of protein complexes and RNA structures as well as a model network of molecules that control how genes switch on and off. They found that evolution tends toward symmetry because the instructions to produce symmetry are easier to embed in genetic code and follow. Symmetry is maybe the most fundamental application of the adage "work smarter, not harder."
"People often are quite amazed that evolution can make these incredible structures, and what we're showing is that it's actually easier than you might think," said Ard Louis, a physicist at the University of Oxford and an author of the study.
"It's like we found a new law of nature," said Chico Camargo, a co-author and a lecturer in computer science at the University of Exeter in England. "This is beautiful, because it changes how you see the world."
Louis, Camargo and their colleague Iain Johnston began their exploration of symmetry's evolutionary origins when Johnston was working on his Ph.D., running simulations to understand how viruses form their protein shells. The structures that emerged were highly biased toward symmetry, cropping up far more often than pure randomness would allow.
The researchers were surprised at first, but it made sense — the algorithms to produce simple, repeating patterns are easier to carry out and harder to screw up.
Because it's easier to encode instructions for building simple, symmetrical structures, nature winds up with a disproportionate number of these simpler instruction sets to choose from when it comes to natural selection. That makes evolution a bit like a "biased game with loaded dice," Camargo said, producing disproportionate symmetry because of its simplicity.