Homo Erectus Held On Until 100,000 Years Ago In Indonesia

The three year old article quoted below speculates that some Southeast Asians may have a small amount of Homo Erectus ancestry. But I think that this is unlikely to have happened directly, due to the lack of overlap in human and Homo Erectus occupation and genetic differences too great to permit the birth of a hybrid individual (although it could be that modern humans dealt the death blow to relict Homo Erectus when they first encountered them en route to Australia and Papua New Guinea, which contrary to the Science article, happened closer to 70,000 years ago, perhaps shortly after the volcanic Toba eruption in Indonesia ca. 74,000 years ago).

But, it isn't inconceivable that an archaic Denisovan individual, a sister species to the Neanderthals and one source of archaic hominin admixture in modern humans, might have admixed with Homo Erectus, with whom they probably co-habited in Indonesia for thousands of years, leading to a small proportion of a modern human with Denisovan ancestry's Denisovan sourced DNA including Homo Erectus ancestry (perhaps about a percent of a percent, i.e. a few parts per 10,000). Indeed, there are some hints in Denisovan DNA of small amounts of admixture with H. erectus, although this is too small to be definitively identified separately in modern humans with Denisovan ancestry (which can be as high as about 5% of some aboriginal Australians and Papuans and Negritos from the Philippines today).

The time coincidence with the genetically estimated most recent common ancestor of Neanderthals and Denisovans, however, is a pretty close match to the time that H. erectus disappears in the archaeological record outside Indonesia, which also isn't that remote from the first appearance of modern humans. Therefore, it wouldn't be unreasonable to guess that modern humans, Neanderthals, and Denisovans were the cause of the extinction of H. erectus in their respective regions. 

If so, Denisovans may have been a very late arrival to the island of Java (i.e. ca. 100,000 years ago or later) and cohabited with them only briefly, which could explain the ability to H. erectus to persist there while going extinct everywhere else. It could also be the case that Denisovan's brought about the extinction of H. erectus in Indonesia tens of thousands of years before modern humans arrived on a path cleared by the Toba eruption.

H. floresiensis a.k.a. "hobbits" also co-habited in Indonesia with H. erectus and Denisovans (and possibly even modern humans), although it is unclear when they first appeared on the island of Flores. But, they were probably an even more basal (i.e. archaic) species of hominin than H. erectus such as H. habilis. So, they probably didn't directly admix genetically with Denisovans or modern humans due to their large genetic distance from them.

When seafaring modern humans ventured onto the island of Java some 40,000 years ago, they found a rainforest-covered land teeming with life—but they weren’t the first humans to call the island home. Their distant ancestor, Homo erectus, had traveled to Java when it was connected to the mainland via land bridges and lived there for approximately 1.5 million years. These people made their last stand on the island about 100,000 years ago, long after they had gone extinct elsewhere in the world, according a new study assigning reliable dates to previously found H. erectus fossils. 

. . . 

The newly dated fossils also bookend the existence of a remarkably long-lived human species, says Patrick Roberts, an archaeologist at the Max Planck Institute for the Science of Human History in Jena, Germany, who wasn’t involved with the study. 

. . .

H. erectus arose in Africa about 1.9 million years ago. These toolmakers with relatively large brains migrated out of Africa and across Asia, crossing into Java by land bridges about 1.6 million years ago, when savanna-like open woodland covered much of the land. Later, sea levels rose, isolating these ancient Javans on an island. Meanwhile, in Africa and mainland Asia, H. erectus disappeared by about 500,000 years ago. 

. . . 

In 2008 and 2010, [the new study’s lead author, paleoanthropologist Russell] Ciochon’s team re-excavated the site, turning up 867 new fossils belonging to deer, wild cattle, and an extinct, elephantlike animal called a stegodon. Based on photographs and documents from the original excavation, they established that some of the newly found animal fossils came from the same rich bone bed as the H. erectus fossils. The researchers applied five types of radiometric dating, including a new method that provides both minimum and maximum dates, to those animal fossils and the sediments around them. The team concluded that the bones were buried between 117,000 and 108,000 years ago, the researchers report . . . in Nature.

From Science (reporting on a December 18, 2019 article in Nature).