Why Does Life Keep Evolving These Geometric Patterns?
A global catalog shows how creatures across the tree of life balance rigidity with flexibility in remarkably consistent ways
The same tile structures with soft joints between are found across the tree of life, including on mirror spiders’ abdomens.
Manoj Kumar Tuteja/Getty Images
The mirror spider can rapidly shift a patchwork of minuscule reflective plates underneath its abdomen’s outer surface, altering the pattern of mirrorlike flashes. This uncommon display comes from common building blocks: Similar tilelike arrangements of plates and soft joints appear throughout the tree of life, from turtle shells to tropical fruit peels. Researchers have now compiled 100 examples of this pattern across animals, plants, microbes and viruses, which they describe in PNAS Nexus.
Study co-author Mason Dean, a biologist at City University of Hong Kong, first noted a regular tiled pattern in micro computed tomography scans of a ray skeleton. He was surprised to find that what looked like pixelated graininess was actually a mosaic of tiny hexagons and pentagons packed edge to edge across the cartilage. Humboldt University of Berlin zoologist Jana Ciecierska-Holmes, also a co-author, began looking for tile examples and was similarly surprised to spot intricate interlocking plates on the outer coating of millet seeds. They and their colleagues set out to determine just how widespread such tiling patterns were.
Chitons’ shell plates and girdles.
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The researchers focused on true tessellations, in which geometric tiles are discrete structural pieces separated by softer seams, rather than purely visual or hollow patterns such as animal coloration or honeycombs. To compare such systems across very different organisms, they created a framework describing what different natural tiles are made of, how they’re shaped, how they connect and what they do. The results reveal structural parallels across many organisms without any shared ancestry.
Salak fruit’s outer covering.
Chitons evolved articulated shell plates, whereas sharks developed tessellated cartilage—two tiled structures that arose independently in distant evolutionary lineages, the researchers found—and microscopic amoebae build architecturally similar protective casings from scavenged mineral tiles. Other variants tile the lenses of insect eyes and form corky plate patterns in the elephant’s foot plant. Across kingdoms, the same basic layout helps animals see, move and protect their bodies.
The recurrence reflects how geometry and growth push organisms toward the same solutions. Predominantly six-sided patterns such as those on sharks and rays are a classic way to efficiently cover curved surfaces, for instance. Dean also notes that tile borders often align with regions where new cells are added during growth, allowing tissues to function as they expand. Plus, pairing hard tiles and softer seams balances stiffness and flexibility, adds Kiel University zoologist Stanislav Gorb, who was not involved in the study. “Too rigid a structure is good for resisting forces but poor for generating motion.”
Armadillo lizards’ bony plates.
Nature Picture Library/Alamy (top); Life on white/Alamy (bottom)
The authors hope their online catalog becomes a living resource to help people recognize these patterns in the organisms and structures they study. “Once you start paying attention to that, you see it everywhere,” Dean says. Ciecierska-Holmes agrees: “You kind of go into the tessellation world.”
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