Researchers uncover a mechanism that may explain why biology consistently selects one molecular form over its mirror image. A new study suggests that life’s long-standing preference for one “handed” version of molecules, known as homochirality, may stem from a subtle quantum effect: electron spin. Researchers found that when electrons move through mirror-image molecules, their spin interacts differently with each form, causing small but meaningful differences in behavior during dynamic processes like chemical reactions or electron transport. Although these molecules are chemically identical in static conditions, this spin-driven asymmetry could make one version consistently more efficient over time, gradually leading to the dominance of a single “hand” in biology. The findings point to a surprising role for quantum physics in shaping the fundamental structure of life.
A team of scientists has identified a new physical mechanism that could help explain one of the most persistent mysteries in science: why life consistently uses one “handed” version of its molecules and not the other.
In a new study led by Prof. Yossi Paltiel of the Center for Nanoscience and Nanotechnology at Hebrew University and Prof. Ron Naaman of the Weizmann Institute , researchers show that electron spin, a fundamental quantum property, can cause mirror-image molecules to behave differently during dynamic processes, even though they are otherwise identical.
Many molecules essential to life come in two mirror-image forms, known as enantiomers. Chemically, these forms are nearly indistinguishable. Yet in living systems, only one version is typically used: amino acids are almost exclusively one type, while sugars follow the opposite pattern.
This phenomenon, known as homochirality, has puzzled scientists for more than a century. Existing explanations have struggled to account for why one specific version was selected globally.
The new study suggests that the answer may lie not in the molecules themselves, but in how they behave when electrons move through them.
The researchers found that when electrons pass through chiral molecules, their spin interacts with the molecular structure in a way that is not perfectly symmetric between mirror images.
As a result:
This breaks a long-standing assumption that mirror-image molecules should behave identically in magnitude, differing only in sign.
The study combines theoretical analysis, experiments, and advanced calculations to show that this asymmetry arises from how electron spin aligns within each molecular structure.
Although the two enantiomers have the same energy, their spin-related properties during motion are not exact mirror images, leading to measurable differences in behavior.
Importantly, these differences appear in dynamic processes, such as electron transport and interactions with magnetic environments, rather than in static properties.
These findings offer a possible route toward understanding how one molecular “hand” came to dominate in biology.
If one enantiomer consistently interacts more efficiently with its environment under spin-dependent conditions, even small differences could accumulate over time, leading to a global preference.
This provides a new perspective on how physical processes, rather than purely chemical ones, may have influenced the earliest stages of biological development.
Looking ahead the work opens new directions for research at the intersection of physics, chemistry, and biology:
More broadly, the study suggests that symmetry in chemistry may be more subtle, and more easily broken, than previously thought.
Science Advances
Experimental study
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Dynamic Breaking of Mirror Symmetry in Spin-Dependent Electron Transport through Chiral Media Causes Enantiomeric Excesses
22-Apr-2026