Plate Nº 78 · recorded October 10, 2026
Biology & EvolutionReported finding
Why Snake Embryos Twist Into Right-Handed Spirals: A Gut Explains It
A study of 900+ embryos shows snake bodies outgrow their guts, and the tethered gut forces the lengthening embryo to buckle into a right-handed spiral.
By Elena Vasquez4 min read770 words
In brief
- Researchers analyzed more than 900 snake and limbless squamate embryos from 39 species.
- The study was published in Current Biology in 2026.
- Early embryos coil only right-handed because the yolk always sits on the embryo's left side.
- CT scans revealed a detached gut pillar tethering the lengthening body.
- Near hatching, embryos split roughly 50-50 between right- and left-handed coils.
Snake embryos coil exclusively to the right during their first weeks inside the egg — and a study of more than 900 embryos, published in Current Biology in 2026, now explains why. The embryo's body lengthens faster than its gut, and that mismatch turns the gut into a tether that forces the growing body to buckle and twist into a right-handed spiral.
An international team led by the Canadian Museum of Nature reached this conclusion after combing photographs of 900-plus embryos from 39 snake and other limbless squamate species, and after using CT scans to reveal anatomy hidden inside the coils.
What did the researchers actually find?
The team, which included scientists and students from the University of British Columbia, Carleton University, the University of Ottawa, California State University Los Angeles, and the University of Helsinki, documented a clear pattern: in the first several weeks after eggs are laid, embryos coil only dextrally — to the right, viewed from head to tail.
"We obtained pictures for more than 900 embryos from 39 snake and other limbless squamate species. That's a statistically robust sample," said senior author Dr. Tetsuto Miyashita, an evolutionary biologist at the Canadian Museum of Nature.
Crucially, embryos at these stages lack the muscles to move themselves. "At these stages, the embryos don't have muscles to move with, so different forces are making them coil right-handed," explained lead author Alexandra Weber, now a graduate zoology student at the University of British Columbia. "But we didn't know what's making them do that."
What mechanism did CT scans reveal?
The decisive clue came from collaborator Dr. Raul Diaz at California State University Los Angeles, who scanned embryos with CT imaging. The scans showed a structure the team had never seen: a pillar of gut running through the spiral of the coiled body.
"There's an intestine detached from the rest of the body, surrounded by tendrils of blood vessels from the yolk," Miyashita said.
The mechanism works like this. Snake embryos must lengthen extremely fast to build their signature elongated bodies, but the gut grows more slowly. The detached, slow-growing gut tethers the lengthening body, which buckles and twists.
"It's like when you adjust the length of a strap and the longer, buckling side of the loop twists," Miyashita said.
The direction is fixed by the yolk's position: "The coiling force is directed so the embryos grow to the opposite side of the yolk. And the yolk is always to the left side of the embryo, hence the embryo will always start coiling right-handed," he explained.
Why does the coiling direction change later?
The right-handed spiral does not last. As the yolk shrinks and muscles mature, embryos gain room and the ability to move. "Some remain in right-handed coils, but some recoil to the left side," Weber said. "So half of these near-hatching embryos are right-handed and the other half left-handed."
That shift suggests the earliest coiling direction comes from developmental anatomy and physical forces, not deliberate movement.
How did a pandemic lockdown produce this study?
The project began during the 2020 COVID lockdown, when Miyashita was working from home and needed a research question students could tackle without labs or museum collections. "Every time I saw images of snake embryos in papers, I wondered whether they are right- or left-handed in their coiling," he said.
"Here, out of the COVID lockdown, we uncovered a snake's secret with a startlingly simple approach — just scroll through an album of snake embryos and record which way they are coiling, and take a good look at their anatomy," Miyashita said, contrasting the approach with sophisticated genetic research on Hox genes and enhancers.
What are the study's limitations?
The findings describe a likely mechanism rather than a proven one, and the physical model has so far been tested only against observational and imaging data. The researchers themselves frame the work as preliminary groundwork: "We are now opening the possibility to develop this model further to explain other spiral forms in nature," Miyashita said.
Why do spirals in biology matter?
The study adds snake embryos to a list of natural spirals that scientists are still working to understand — looping intestines, snail shells, and now coiled embryos. "There is a touch of mystery to spirals, and we are only beginning to understand how these shapes are produced in animals," Weber said.
"This all started out with a curiosity to see if snakes are 'handed'," she added. "It was exciting to follow it to deep insights about their evolution."
via nature.ca (Original)
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