Modern humans are the result of different hominin species interbreeding through history, and this latest discovery proves that there are still some contributors that remain a mystery.

Referred to as a “ghost” hominin, research suggests that some people living in West Africa today have traces still active in their DNA.

Unlike our Neanderthal or Denisovan ancestors, no physical evidence or remains of this species have been found.

Researchers from UCLA’s School of Medicine reported in Science Advances that they were looking for segments of archaic ancestry within 400 modern genomes. These came from the 1,000 Genomes Project and largely focused on the Yoruba and Mende populations native to South Africa.

Their computer program found between 2% and 19% of their genetic ancestry was contributed by an unknown source.

The DNA is likely the result of introgression, which is what happens with two populations mate and produce hybrid individuals, and researchers believe it is likely this DNA came from a whole new species of early human.

It’s not surprising that the mystery DNA didn’t come from Neanderthals or Denisovans, as neither are thought to have ever been to Africa, but it does increase the mystery surrounding who it might belong to instead.

That said, this is not the first time we’ve discovered DNA from hominins who were – and have remained – mysteries. DNA from people on the Andaman Islands in Southeast Asia, for example, contained a good number of genes not derived from Neanderthals, Denisovans, or homo sapiens.

The world was a big place full of hominins, it would seem, and perhaps one day archaeology will cough up some answers.

Until then, it’s kind of nice to know that, even in this day and age of technology and science, the history still manages to keep a few secrets.