Researchers at the University of California, Berkeley, have developed a method called TRACE that looks for very old family connections in the genomes of living people. Their findings were published online in the journal Science on July 30.
The team found evidence of a previously unknown human relative, called a ghost lineage, that mixed with the ancestors of modern humans in Africa more than 50,000 years ago. The researchers estimate that its DNA makes up about 0.5 to 1 percent of the genome of each living person they examined, in both African and non-African populations.
The study also found signs of a much older lineage that mixed with Denisovans in Eurasia roughly 1.8 million years ago. Some of that DNA later reached modern humans through Denisovan ancestors, especially in populations in Oceania.
The identities of these ancient relatives are still unknown, and the findings are inferred from patterns in modern DNA rather than from a recovered genome of either group. TRACE gives scientists a way to study parts of human history that left no clear fossil or ancient-DNA record.
