Early snake embryos coil to the right, and a new study offers a physical explanation: their bodies grow faster than their guts. The paper, published Aug. 31 in Current Biology, presents evidence that the lengthening body buckles around a slower-growing intestine, while the position of the yolk sets which way the coil turns.

The team, led by researchers at the Canadian Museum of Nature in Ottawa, gathered images of more than 900 embryos representing 39 species of snakes and other limbless squamates, the reptile group that includes lizards and snakes. In early developmental stages, before the embryos had working muscles, coiling was nearly always right-handed from head to tail.

The finding helps explain how snakes fit an extremely long body inside an egg. It carries no safety implications for people, but it shows how simple physical forces can help shape animal bodies, and how existing museum collections can still produce new discoveries.

A Gut Pillar Inside the Spiral

The key clue came from CT scans by collaborator Raul Diaz of California State University, Los Angeles. The scans revealed a structure the team had not seen before: a pillar of gut, detached from the rest of the body, stretching through the middle of the spiral.

Senior author Tetsuto Miyashita, an evolutionary biologist at the museum, said the embryo speeds up body growth while the gut lags behind. "The body buckles and twists into coiling," he said in the museum's release. He compared the effect to adjusting a strap, where the longer, buckling side of the loop twists.

The museum describes this visceral pillar as a newly discovered trait unique to snake embryos. The gut rejoins the rest of the body later in development, once its own growth catches up.

The direction of the coil comes from the yolk, which sits on the embryo's left side, according to the researchers. The coiling force pushes the growing body toward the side opposite the yolk, so early embryos begin with a right-handed turn.

The pattern does not last. As embryos mature, their muscles develop, the yolk shrinks, and the embryos reposition themselves. Lead author Alexandra Weber, now a zoology graduate student at the University of British Columbia, said some embryos stay right-handed while others recoil to the left, leaving near-hatching embryos split roughly half and half, as Popular Science also reported.

A Pandemic Project Built on Museum Collections

The study grew out of the 2020 COVID-19 lockdowns. Miyashita said he wanted a project students could do without going to a lab or museum, so Weber, then at Carleton University, and two University of Ottawa undergraduates searched published literature and museum collection databases for images of snake embryos.

In the first few weeks after eggs are laid, the embryos appeared to coil only right-handed, according to a news release distributed through EurekAlert. "At these stages, the embryos don't have muscles to move with," Weber said, explaining why some other force had to be shaping the coil. That observation pushed the team to look inside the embryos rather than at their behavior.

The specimens included a plains garter snake embryo held in the Canadian Museum of Nature's collections, along with Cape house snake and African house snake embryos, according to the museum.

The research team included scientists and students from the Canadian Museum of Nature, the University of British Columbia, Carleton University, the University of Ottawa, California State University, Los Angeles, and the University of Helsinki.

Strength of the Evidence

This is a comparative anatomical and imaging study published in a peer-reviewed journal. Its sample is large for developmental work on reptiles, and Miyashita described it as "a statistically robust sample."

The paper's own language is measured. In the published abstract, the authors say they "present evidence" that the rapid formation of body segments outpaces extension of the gut at early stages, and that early coiling direction "appears to be nearly fixed" as right-handed. That is different from an experiment that alters gut growth or yolk position to prove cause and effect.

The images came from many sources, including published papers and museum databases, which means embryos were photographed and staged in different ways. The 39 species studied are also a small slice of the thousands of snake species alive today, so the pattern may not hold everywhere.

Nature World News did not obtain comment from a developmental biologist outside the study team. Readers should see the result as a well-supported explanation for a long-standing puzzle rather than a final answer.

Clues to How Snakes Got So Long

Snakes evolved extremely elongated bodies, and scientists have studied that transformation mostly through genetics, including the Hox genes that help pattern the body from head to tail, Miyashita noted. He said the new work shows that a "startlingly simple approach" can also reveal how that body form takes shape.

The team's explanation is mechanical rather than genetic. A mismatch in growth rates, plus the placement of the yolk, appears to be enough to produce a consistent spiral. That kind of physical explanation can complement genetic research by showing how tissues respond to the forces created as an embryo grows.

The researchers said they hope to develop the model further to explain other spiral forms in nature, and Weber pointed to examples such as the looping intestine and snail shells. That broader idea has not yet been tested, and it will take studies in other animals to know whether the same rules apply.

For wildlife watchers, the study does not change any guidance about snakes or their eggs. It is a reminder, though, that snakes develop through a complex folding process long before they hatch, and that preserved specimens in museum collections can still answer new questions.

The next steps are studies that test the model in more species and at more stages of development. For now, the work offers a well-supported explanation for why young snake embryos turn right.

What Readers Want to Know

What did the study find?

Early snake embryos coil right-handed because the body grows faster than the gut, which forms a pillar-like tether that the body buckles around. The yolk's position on the embryo's left side sets the direction, according to the researchers.

How many embryos were examined?

More than 900 embryos from 39 species of snakes and other limbless squamates, drawn from published images and museum collection databases.

Do all snake embryos stay right-handed?

No. As embryos develop muscles and the yolk shrinks, some recoil to the left. Near hatching, the split is roughly half right-handed and half left-handed.

Is the explanation proven?

The study presents anatomical and imaging evidence, but it did not experimentally change gut growth or yolk position, so the mechanism has not been tested directly.

Does this affect how people should handle snakes or snake eggs?

No. The study is basic developmental research and does not change any wildlife or safety guidance.

Who conducted the research?

A team led by the Canadian Museum of Nature, with researchers from the University of British Columbia, Carleton University, the University of Ottawa, California State University, Los Angeles, and the University of Helsinki.