Homo erectus, probably if not definitely our ancestor, was an extraordinary success. Erectus arose around 2 million years ago in Africa and spread into Eurasia, where it founded a host of hominin subspecies. However, Homo erectus had been thought to have died out about a couple of hundred thousand years ago. Now, though, the robust redating of a fossil bed found almost a century ago in Java, Indonesia, shows the species lasted much longer than had been thought – finally dying out only 117,000 to 108,000 years ago.
The new dating for the fossil site at Ngandong, around 20 meters (65 feet) above the Solo River, is much younger than previous estimates. This makes it the last known stand of Homo erectus, Yan Rizal of Indonesia’s Bandung Institute of Technology, Prof. Russell Ciochon of the University of Iowa and colleagues reported Wednesday in Nature.
The fossils in question are 12 skullcaps and two leg bones identified as erectus. For what it’s worth, these archaic humans (and remains of animals found with them) didn’t die there but upriver, being washed to their final resting place by flooding. All that and other difficulties made robust dating extremely difficult.
The Homo erectus remains found at Ngandong had been identified as the youngest, most advanced form of the species found so far. The site, however, had been thought to be much older. The new dating results at regional, valley and local scales “negate the extreme ages that have been proposed for the site and solidify Ngandong as the last known occurrence of this long-lived species,” the team writes.
The rise of Homo erectus
Direct lineages in human evolution remain obscure. About the only thing we are clear on is that our evolution was not a neat linear succession from knuckle-dragging ape to proud-standing human. Since splitting off from the chimp line (Pan) 6 to 7 million years ago, the Homo line split time and again. It has become clear that multiple species of early humans coexisted and often interbred, which has led to much argument over the definition of “species.”
Homo erectus (“upright man”) is thought to have arisen from a late australopithecine. It remains unclear whether either australopiths and/or erectus were directly ancestral to us. Most agree that erectus at least likely was. To be sure, erectus was the first known hominin to have limb proportions reminiscent of modern humans – short arms and long legs. Its height was comparable to ours, but its face was flatter.
The bottom line is that Homo erectus began in Africa, where it may have evolved into us, eventually, and spread to Asia and possibly Europe too. (There are arguments over whether Europe’s Homo heidelbergensis is just a variant of erectus.) As it roamed, long-legged erectus reached the Indonesian islands over 1.5 million years ago.
And that is where the last of its kind died out, according to the new dating of the Ngandong fossil bed. Its descendants, meanwhile, would live on for a while.
Two diminutive species of extinct midget humans discovered fairly recently – Homo floresiensis (“the hobbit”), on the Indonesian island of Flores, and Homo luzonensis, on the Philippines island of Luzon – are now widely thought by anatomists to have descended from Homo erectus.
At first, when the evidence for the pint-size people was found, the assumption was that they were modern humans that had undergone island miniaturization, or suffered from dwarfism or some other problem. Subsequent discoveries and analyses revealed that floresiensis and luzonensis had archaic traits reminiscent of erectus, not sapiens.
In any case, both are long gone: Floresiensis seems to have died out about 60,000 years ago: pygmies living on the island today are not their offspring but are definitely modern humans. Luzonensis apparently went extinct 67,000 years ago.
Did our forefathers meet any of these other species? Maybe.
Anatomically modern humans are thought to have reached southeast Asia around 65,000 years ago. This was clearly not the first modern human exit from Africa, but earlier ones evidently went extinct. There may have been, and probably were, overlaps between the species, but the researchers don’t believe they met erectus, which was gone by then.
On the other hand, early modern humans trekking or boating through the islands may well have encountered the tiny hominins living on Flores – but there’s no evidence for it.
Another species prowling that neck of the woods was Denisovans, who split off from Neanderthals in Asia (or were a Neanderthal variant, depending who you ask). Remains of Denisovans have been found in Siberia and, recently, Tibet and DNA analyses have strongly indicated that they reached southeast Asia too.
We note that analyses of modern human DNA has shown interbreeding with Neanderthals and Denisovans and probably other species as well.
But: a residual signal of archaic DNA in certain modern regional populations in southeast Asia lies outside the Homo sapiens-Neanderthal-Denisovan clade, the team writes. It came from somebody else.
Since Homo sapiens in Asia and erectus in Asia did not coexist, the thinking is that modern humans got this signal from the Denisovans they mated with, who had, earlier, mated with a late-surviving group of Homo erectus. Irrespective of direct lineage, some of us may, after all, have a direct trace of erectus in our genes.