Constraints on the Origin of Biological Homochirality: From Left-Handed Life to Replication Efficiency as a Function of Enantiomeric Excess

Biological life on Earth exhibits near-complete homochirality: amino acids are predominantly L-handed and sugars predominantly D-handed. The origin of this molecular asymmetry remains one of the central unresolved problems in origin-of-life research. This manuscript develops a constraint-based framework for evaluating competing explanations of biological homochirality, integrating evidence from extraterrestrial amino acid measurements, amplification mechanisms, mineral-catalyzed polymerization, template-directed replication chemistry, and astrophysical circularly polarized light. Rather than asking which single mechanism “caused” chirality, the analysis reframes the problem in operational terms: how does replication rate and fidelity depend on enantiomeric excess? Experimental anchor points from template-directed oligomerization, cross-inhibition studies, and mineral-catalyzed enantioenrichment are assembled to constrain the likely shape of this replication–chirality relationship. The synthesis suggests that near-complete homochirality was unlikely to have preceded all replication-like chemistry, but substantial enantiomeric enrichment was likely required before efficient RNA-based genetic systems could emerge. The manuscript identifies a decisive experimental program—measuring replication efficiency as a function of enantiomeric excess—that would significantly reduce remaining uncertainty.