“Alongside Neanderthal and Denisovan DNA, human genomes preserve traces of two other relatives no one can identify. Neither has a sequenced genome or a confirmed fossil, and part of one may be sitting in your DNA.
Researchers call one the “ghost” lineage. A new study found one of its signals in a region containing FOXP2, a gene involved in speech and language. Very little Neanderthal or Denisovan DNA has been found there, so the region often seemed distinctly modern human. Yet at one point, ghost ancestry appeared in about 13 out of every 100 copies of that region researchers analyzed.
Published in Science, the research maps both lineages and estimates when their DNA entered other human groups. The ghost lineage interbred directly with our ancestors in Africa, while the much older “super-archaic” lineage reached Homo sapiens through Denisovans.
“We often think of human evolution as a branching tree, but new genomic data and analytical methods reveal a much more interconnected history — more like a complex web of populations connected by repeated episodes of migration and mixing,” said senior author Priya Moorjani in a press release.
How Ghost and Super-Archaic DNA Reached Modern Humans
Ghost DNA appeared in every population examined, placing the interbreeding before modern humans spread beyond Africa around 50,000 years ago. It accounts for approximately 0.5 to 1.1 percent of their genomes.
The lineage split from ours around 830,000 years ago. Its age overlaps with Middle Pleistocene Homo groups in Africa, possibly including Homo heidelbergensis, but no genetic match exists.
The super-archaic lineage separated from ours around 1.8 million years ago. Its DNA entered Denisovans more than 200,000 years ago before reaching Homo sapiens through later interbreeding.
Researchers followed the trail through 92 genomes containing high levels of Denisovan ancestry. Super-archaic fragments represented about 0.3 percent of the Denisovan ancestry detected, a figure the team considers a conservative minimum.
Homo erectus lived during the right period to be a possible source, although the connection remains unconfirmed.”