Gene Discovery Reveals How Snail Shells Coil Left or Right

In a mountain valley deep in rural Japan, researchers found something that most of the animal kingdom does not permit: snails that spiral in opposite directions, living together, breeding together, and thriving. This discovery led scientists from the University of Nottingham and Tohoku University to identify the genetic mechanism behind one of biology's most fundamental mysteries—why bodies have a handedness at all, and why most animals are locked into one orientation while snails are not.

The question is deceptively simple. Most snail shells coil to the right, like a spiral staircase ascending clockwise. But some coil left. For decades, researchers knew this variation existed but had no explanation for it. The answer, it turns out, lives in a single gene that produces a protein called myosin. Myosin is a molecular machine that helps cells move and reshape themselves. Small variations in this protein, the team discovered, cause cells to twist in opposite directions during the earliest stages of development—either clockwise or counterclockwise. That initial twist sets the entire trajectory for how the snail's shell and internal organs will form.

What makes this finding remarkable is not just that the gene was identified, but what it reveals about flexibility in nature. In most animals—humans included—body asymmetry is locked in place. Our hearts sit on the left side of our chests. Our livers dominate the right. Reversals of these organs are rare and usually signal something has gone wrong during embryonic development. But the Japanese snails the researchers studied do not follow this rule. Both the left-coiling and right-coiling versions develop normally, without disease, without pathology, without any apparent cost. Both types are ancient lineages, suggesting this flexibility has persisted for a very long time. The left-coiling variant even shows genetic signatures of natural selection, meaning it has been actively maintained by evolution.

The researchers made this discovery by studying Euhadra snails in a specific location where left and right-coiling snails can mate. In most snail species, this is impossible—the reproductive organs are positioned on opposite sides of the body, making cross-mating mechanically unfeasible. But in this valley, both types coexist and interbreed, allowing the team to trace the genetic basis of the difference. When they compared their findings with pond snails, where left-coiling is rare, they found a starkly different picture. In pond snails, a mutation in a different gene does produce left-coiling shells, but it comes with a price: abnormal embryonic development. The snails survive, but they are malformed.

This contrast points to something deeper that remains unsolved. Snails use the same molecular building blocks as every other animal—the same proteins, the same chemical chirality. Yet somehow they have evolved the ability to assemble those identical components into bodies and shells that spiral in opposite directions, both equally viable. Most animals cannot do this. The question of why—why snails alone possess this flexibility, and why other animals are constrained to a single orientation—remains a frontier in developmental biology. The work was published in Current Biology and arrives at a moment when the scientific community has just recognized the importance of chirality itself: researchers studying how molecular handedness shapes living systems were awarded the Nobel Prize the week this discovery was announced.