Only a day after scientists unveiled the discovery of an enigmatic new human species in the Philippines, Kiwi biologists say they might have found another in southeast Asia.
Researchers from Massey University analysed genetic data collected from the region, and particularly the island of New Guinea, and found distinct genetic lineages of the mysterious Denisovan people, whose existence was only discovered a decade ago.
The evolutionary split between Denisovans and the lineage that lead to modern humans - Homo sapiens - happened approximately 740,000 years ago. The first trace of them was discovered in a Siberian cave in 2010.
But it now appears the Denisovans might have split further into completely different species of human.
"We used to think it was just us - modern humans - and Neanderthals," said Murray Cox of Massey University, who led the new study.
Cox's team looked at 161 genomes from 14 different island groups across southeast Asian islands, including New Guinea. They found "hundreds" of gene variants from two "deeply divergent" lineages that appear to have been separated for 350,000 years.
"We now know that there was a huge diversity of human-like groups found all over the planet - our ancestors came into contact with them all the time," and bred with them, says Cox.
The study, published in journal Cell Press, says they're so different they "really should be considered as an entirely new archaic hominin species".
Previous research has found that after splitting from the line that would go on to become Homo sapiens, the Denisovans and Neandarthals only took about 300 generations to split into two distinct species - so 350,000 years would be more than enough time, if separated, to form new branches of the genus Homo.
Papuans have about 6 percent Denisovan DNA, and Aboriginal Australians 3 to 5 percent, according to prior studies.
Other species discovered in recent years include Thursday's Homo luzonensis (the Philippines), Home floresiensis (Indonesia, discovered in 2004) and Homo naledi (South Africa, 2015).
Researchers expect to uncover more proto-humans in southeast Asia in coming years, saying the region has been "incredibly understudied". Most prior research has focused on Europe and northern Asia, because its colder temperatures have preserved bones better.
But, as this latest study shows, technology is now letting scientists discover new strains of ancient human by studying those living today, and detecting DNA evidence of their distant ancestors.