Our genome contains traces of two mysterious human groups

A new study has revealed traces of two previously unknown human groups within the genomes of modern humans. Researchers have identified genetic segments originating from these mysterious populations, which intermingled with early human ancestors before the exodus from Africa. The findings were published in the journal Science and were based on analysis of genome data from over 500 individuals. The research team, led by Priya Moorjani of the University of California, Berkeley, developed a novel method called TRACE to reconstruct ancestral recombination graphs from contemporary genomes. This technique allows scientists to trace the evolutionary history of specific DNA segments without requiring ancient reference genomes. By analyzing patterns of genetic inheritance and recombination, the researchers uncovered evidence of two additional archaic human lineages that left behind genetic footprints in present-day populations. One of these lineages appears to have mixed with early human ancestors prior to the major dispersal of Homo sapiens out of Africa. The other lineage is so ancient that its genetic contribution can only be detected through indirect means. These findings add to the growing body of evidence suggesting that modern humans have a complex ancestry involving multiple interbreeding events with extinct hominin species such as Neanderthals and Denisovans. The TRACE method works by identifying segments of DNA that exhibit unusual patterns compared to random genetic variation. These segments are longer than typical inherited fragments and show signs of having originated from a population that split off earlier in evolutionary history. By mapping these anomalies, the researchers were able to infer the presence of previously undocumented human lineages. In their analysis, the team found that approximately 0.5 to 1.1 percent of the genome in each individual comes from this "ghost" lineage. This genetic contribution is observed in both African and non-African populations, indicating that the mixing occurred well before the widespread migration of modern humans beyond the continent. The genetic material shared among non-Africans suggests at least one interbreeding event took place in regions south of the Sahara. Yulin Zhang, the lead author of the study, explained that the researchers were able to pinpoint specific genomic locations that likely originate from this ghost lineage. They demonstrated that this genetic contribution is present in all modern humans, not just those of African descent. This discovery challenges previous assumptions about the simplicity of human ancestry and highlights the complexity of our evolutionary past. The study’s implications extend beyond understanding human origins. It offers insights into how genetic diversity arises and persists over time, even in the absence of direct fossil records. As more genome data becomes available, similar methods could help uncover other hidden branches of the human family tree, further enriching our knowledge of prehistoric human interactions.