For as many ancient ancestors of humanity as we know, some remain a mystery, with only faint traces of DNA in our genes today as evidence of their existence.

As reported by Science, researchers at the University of California, Berkeley, have found evidence of two previously unknown human relatives hiding in our modern human genes. Scientists already knew that humans got some of their DNA from Neanderthals and Denisovans, but some genes still trace back to unaccounted-for family members.

Using a new computational technique called TRACE, researchers analyzed more than 500 modern human genomes and reconstructed ancient genealogies without needing DNA from the extinct populations themselves. They found evidence of one “ghost” lineage that interbred with Homo sapiens in Africa more than 50,000 years ago. Its DNA now accounts for roughly 0.5 percent to 1 percent of the genomes of people around the world.

Researchers Found DNA From Mysterious Human Ancestors We Never Knew Existed

The second lineage is so old the researchers call it “super-archaic,” tracing it to a population that split from our evolutionary line about 1.8 million years ago. That group seems to have interbred with Denisovans more than 200,000 years ago. Its DNA stuck around and eventually made its way into modern humans through our Denisovan ancestors.

We still don’t know exactly who these ancient relatives were, but there are theories. Homo heidelbergensis was an older lineage, living between 700,000 and 200,000 years ago across Europe and Africa. The other could be related to Homo erectus. Specific DNA traces of either group have not yet been found.