Ancient proteins reveal H. erectus bred with Denisovans

Scientists have extracted ancient proteins from the tooth enamel of six Homo erectus individuals who lived in China approximately 400,000 years ago, marking the first genetic evidence of interbreeding between H. erectus and Denisovans. The research, published in Nature, analyzed teeth from three sites in China: Zhoukoudian (the famous "Peking Man" location), Hexian in southern China, and Sunjiadong in central China. The team, led by Qiaomei Fu at the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, successfully sequenced protein fragments from nine enamel proteins in specimens belonging to five males and one female. The analysis revealed two significant amino acid mutations in the ameloblastin protein shared by all six specimens. The first mutation, AMBN(A253G), involves glycine replacing alanine at position 253 and has not been observed in any other human relative tested, including an older H. erectus specimen from Georgia, suggesting it may be a unique genetic signature of East Asian H. erectus populations. The second mutation, AMBN(M273V), where valine replaces methionine at position 273, had previously been identified in Denisovans and persists in some modern human populations today, appearing at frequencies of 21 percent in the Philippines, 1.17 percent in India, and 0.71 percent in Papua New Guinea. This genetic evidence indicates that H. erectus populations in East Asia passed the AMBN(M273V) variant to Denisovans through interbreeding, and modern humans subsequently inherited this genetic legacy when our ancestors interbred with Denisovans. Analysis of older Denisovan specimens from Harbin in northern China and Siberia, both dating to over 150,000 years ago, show both the original and derived variants, suggesting they inherited the mutation from one parent with H. erectus ancestry. The findings also resolve a long-standing debate, confirming that the Hexian specimens belong to H. erectus rather than Denisovans, despite earlier morphological suggestions to the contrary.