New research suggests there may be a genetic link between Homo erectus, Denisovans, and modern human populations in Southeast Asia and Oceania. Scientists from the Chinese Academy of Sciences analyzed protein mutations in 400,000-year-old Homo erectus teeth found at three fossil sites in China: Zhoukoudian (also known as Peking Man), Hexian, and Sunjiadong. By examining the enamel proteins in these ancient teeth, they identified two specific mutations: AMBN A253G and AMBN M273V. The AMBN M273V variant had previously been found only in Denisovans, a mysterious group of ancient humans known mainly from DNA recovered from a single finger bone and a few teeth found in Siberia. However, the new findings suggest this mutation was also present in Homo erectus, which may indicate a transfer of genetic material from Homo erectus to Denisovans, and later to modern human populations in Southeast Asia and Oceania through interbreeding or other forms of genetic exchange. The study also highlights the potential of AMBN A253G as a molecular marker, which could help identify Homo erectus populations as part of a shared evolutionary group. This marker, along with the AMBN M273V variant, might help scientists better understand the relationships between different ancient human species and their contributions to the genetic makeup of modern humans. The research team developed new techniques in the field of paleoproteomics, which involves studying proteins preserved in ancient remains. These methods allow scientists to extract molecular information from fossils with minimal damage, offering a more detailed look into the biology of ancient hominins. One of the new techniques involves using the male-specific enamel protein AMELY to determine the sex of ancient individuals. This method was cross-checked with advanced laboratory tools such as tandem mass spectrometry and multiple data analysis pipelines, ensuring the accuracy of the results. These innovations in paleoproteomics are expanding the ways scientists can study ancient human biology, even when DNA is too degraded to be useful. The findings, published in the journal Nature, offer new insights into the complex web of genetic interactions among ancient human populations. By identifying shared genetic markers between Homo erectus and Denisovans, and their potential presence in modern human populations, the study opens up new avenues for understanding how different groups of early humans interacted and evolved over time.