An article published in the journal “Nature Ecology & Evolution” reports a genetic study on populations of Island Southeast Asia that shows the presence in their DNA of genes inherited from the Denisovans, another human species now extinct, but no trace of interbreedings with other hominins of which there are fossils. A team of researchers led by Dr João Teixeira of the Australian University of Adelaide examined the DNA of 426 people from 10 different populations looking for possible traces of interbreedings with so-called super-archaic populations but without results.
Island Southeast Asia, or maritime Southeast Asia, the geographical area that includes Brunei, Indonesia, Malaysia, Philippines, Singapore, and East Timor, is interesting from a paleoanthropological point of view because fossil discoveries indicate the presence of various species of hominins over the millennia. Homo erectus reached the island of Java (Photo© Peter Maas) and at least two species lived on various islands, perhaps even until the arrival of Homo sapiens: Homo floresiensis in today’s Indonesia and Homo luzonensis in today’s Philippines.
Various discussions exist on the taxonomic classification of Homo floresiensis and Homo luzonensis. Theories about Homo floresiensis propose that it was closely related to Homo erectus or that it’s an even more archaic species of the genus Homo that migrated independently from Africa. For Homo luzonensis the situation is even more complicated because the specimens discovered have characteristics similar to those of various other species of hominins, some so archaic as to make them similar to australopithecines.
The fossil record of hominins in that area is rich and leaves open discussions on possible interbreedings with the Homo sapiens who arrived in that area. João Teixeira’s team tried to look for traces of such interbreedings with these so-called super-archaic populations by examining the DNA of 426 people from 10 different populations. The results don’t show genetic characteristics that could suggest that type of interbreedings while confirming that many Asian populations inherited genes from the Denisovans, an ancient human species now extinct.
The situation is curious, in the sense that various fossils of different species of hominins that lived in today’s Island Southeast Asia are available but no traces of interbreedings with Homo sapiens have been found while no fossils of Denisovans have been found but their genetic traces are widespread.
The Denisovans are known only for a few fossil bones discovered mainly in Siberia which have been preserved so well that it was possible to extract DNA. That allowed to reconstruct the relationships with Homo sapiens and Neanderthals discovering some interbreedings that even today have still left some of their genes in many populations of Homo sapiens.
These results show once again the difficulties that exist in the reconstruction of the history of humanity. The development of paleogenetics, which studies the DNA of extinct species, made it possible to discover interbreedings between various species of hominins but only some fossils are in such a state of conservation that pieces of DNA are still intact. The hominin bones discovered in Island Southeast Asia are too degraded from that point of view, so paleontologists and paleoanthropologists have to reconstruct the history of those populations based on other types of evidence.
It’s possible that those super-archaic species never interbred with Homo sapiens and Denisovans, or scientists are unable to find the genetic traces of those interbreedings. A hypothesis offered by the researchers is that Homo floresiensis or Homo luzonensis, or both species, are not actually super-archaic but are a branch of the Denisovans. For now, it doesn’t seem possible to verify this hypothesis but new discoveries could change the situation.