Gene sharing has stabilised the genetic code

The genetic code is nearly universal across life. Yet, The National Center for Biotechnology Information (NCBI) genetic code table recognises 27 distinct variants, most of which are confined to eukaryotic nuclei and organelles. Comparative genomics and synthetic recoding studies reveal that the code is far more flexible than once believed, but why has the standard code remained so remarkably conserved among prokaryotes? Here, we propose that horizontal gene transfer (HGT) acts as a stabilising evolutionary force by enforcing translational compatibility among gene-sharing organisms. In prokaryotes, extensive HGT among prokaryotes creates strong selection for code uniformity, whereas genetic isolation in eukaryotes, driven by sexual reproduction, compartmentalisation, and reduced DNA exchange, has permitted divergence. This dynamic parallels human languages: communities that communicate frequently maintain a shared language, while isolated groups develop distinct ones. Although mobile genetic elements can locally perturb decoding through recoding and translational hijacking, these effects rarely propagate across microbial communities. We argue that the near universality of the genetic code is not a frozen historical accident but an emergent property of dense microbial connectivity shaped by HGT.