Proteins extracted from four P. robustus teeth in Swartkrans cave South Africa. Mass spectrometry sequenced 400 amino acids from tooth enamel proteins. Amelogenin-Y protein identifies two male teeth. X chromosome proteins identify two female teeth. Evolutionary tree places P. robustus distantly from Homo sapiens. Neanderthals Denisovans and H. sapiens cluster closer together than to P. robustus. Protein data oldest ever from hominin at 2 million years. Proteins more resilient than DNA for ancient fossils. P. robustus lived 1.2-2 million years ago in South Africa. Technique analyzes amino acid sequences to build protein relations mirroring species evolution. Less variable proteins in P. robustus limit tree informativeness. Data pushes hominin genetic records further back in time and place. Debate persists on protein utility for hominin phylogeny clarity.