Why all life uses the same protein recipe, across billions of years

By analyzing thousands of proteomes from bacteria to viruses, researchers discovered that despite radical evolutionary divergence, all life maintains nearly identical ratios of carbon, nitrogen, oxygen, and other elements in their proteins. Ancient reconstructions of early life and experiments with simpler amino acid alphabets showed this elemental constraint emerged early and wasn't accidental—primitive proteins using fewer amino acids either couldn't fold properly or fell outside this narrow range, suggesting chemistry filtered which amino acids could survive.