Homochirality of life
Why does life on Earth use almost exclusively 'left-handed' amino acids and 'right-handed' sugars, when the same basic chemistry could in principle work equally well with the mirror-image molecules, and what process originally broke this molecular symmetry?
History and references
Still open in the literature as of 2026.
Louis Pasteur discovered in 1848 that tartaric acid crystals come in two mirror-image forms, launching the study of molecular chirality (handedness). Life on Earth overwhelmingly uses only left-handed amino acids and right-handed sugars, a striking uniformity called homochirality, since a random abiotic start would be expected to produce roughly equal mixtures of both mirror forms. Numerous mechanisms have been proposed to explain how this symmetry could have been broken and then amplified early in life's origin — from subtle physics (parity violation in beta decay) to chemistry (autocatalytic amplification of tiny initial imbalances) to astrophysics (circularly polarized starlight preferentially destroying one chiral form in interstellar ice) — but no single explanation has been established as the actual historical cause.
Every protein in your body is quietly, uniformly 'left-handed' for no reason chemistry alone can explain, a molecular fingerprint of whatever accident first tipped the scales toward life.
Explanations that circulated
- That the weak nuclear force's tiny parity violation has been proven to be the origin of biological homochirality — this is one long-standing hypothesis among many (others include circularly polarized light from star-forming regions, mineral surface catalysis, random symmetry-breaking amplification), but none has been confirmed as the actual historical cause
References
- The Mystery of Homochirality on Earth, Life (MDPI), 2024
Solutions 0
Sign in or create an account to publish a solution