Primitive yet recent jawbone from Taiwan; Penghu 1

An article published in Nature Communicatons on Jan. 27, 2015 describes a mandible belonging to an archaic Homo species from Taiwan, known as Penghu 1. The bone, a lower jawbone with some teeth is remarkable because it displays robust primitive features which do not appear in other contemporary hominids. It is recenty yet primitive.

The authors propose that Penghu 1 is a survivor of "multiple evolutionary lineages among archaic hominins before the arrival of modern humans in the region." [1]

There is a growing body of evidence showing that Asia was not a dead end for human evolution, the notion that H. erectus settled there after leaving Africa and died out or was replaced by modern Humans 50 kya is being refuted by new findings.

The age of Penghu 1's remains is a bit uncertain: "younger than 450 ka, and most likely 10-70 ka or 130-190 ka." [1], which is very recent for primitve features and definitively too primitive to be H. sapiens.

The interesting part is that Penghu 1 is a mossaic of Chinese, Asian and non-Asian archaic jawbones. It is very similar to the Hexian remains (found in China, 590 mi - 950 km north of the Penghu 1 site), which have been placed within the H. erectus line and have been dated to 400 - 150 ka (there is controversy about this date). So this opens the door to some possible link between H. erectus and the Penghu 1 man.

Penghu 1 lacks some features found in Eurasian Neanderthals (so it is not derived from Neanderthals meandering across Asia into Taiwan).

What is remarkable is the survival until such recent dates of teeth that are so large, and set in thick mandibles. This is a very primitive trait. But how does Penghu 1 fit into our ancestral family treee? The authors suggest that:

Several different models can be proposed to explain this situation. First, such morphology may be primitive retention from earlier Asian Homo. Because H. erectus mandibles from the terminal Early or early Middle Pleistocene of Java and China had already acquired thinner corpus and smaller molars, this hypothesis implies the presence of another longstanding Homo lineage in Asia that continued from the Early Pleistocene.
Otherwise, there may have been a migration of robust-jawed Homo from Africa, possibly bringing along Acheulean stone tool technology around the terminal Early Pleistocene, who later evolved some unique morphology locally. Both hypotheses cast doubt on the traditional view that H. erectus was the sole hominin species on the Asian continent in the Early to early Middle Pleistocene... [1]

In other words their hypothesis 1 suggests that an "earlier Asian Homo" had thick jaws and big molars and that these archaic features were inherited by a later group that descended from these primitive Homos (that is what "primitive retention" means: they retained an archaic feature). This means that this archaic lineage survived and was contemporary with the smaller jawed H. erectus that coexisted with Penghu 1.

While hypothesis 2, proposes that some thick jawed Africans bearing Acheulean toolage, reached Asia in the final stages of the Early Pleistocene (which ended 781 kya), and that they evolved separately from the extant and contemporary H. erectus that were already living there, and who had more gracile jaws.

In the first case mentioned above, Who was this ancient Asian? Perhaps some surviving H. habilis? that left Africa before H. erectus? and survived until recently?

In the second case, which African group used Acheulean toolage and migrated out of Africa 780 kya? This was later than the wave of H. erectus that peopled Asia. Did these more recent heavy jawed Africans cross Asia to Taiwan through H. erectus populated China? We can rule out H. heidelbergensis because the paper says that Penghu 1 "1 lacks a suit of uniquely derived morphology of west Eurasian H. neanderthalensis (and in part its Middle Pleistocene predecessor, ‘H. heidelbergensis’)." [1]. So who is the ancestor?

The authors point out that "Figure 7b also suggests that Penghu 1 is similar to ‘Denisovans’14 in M2 crown size; however, a direct comparison is not possible as there are no mandibles and mandibular teeth associated with this enigmatic Siberian hominin" [1], suggesting similarities with Denisovans...

Sources

Chang, C.-H. et al. The first archaic Homo from Taiwan. Nat. Commun. 6:6037 doi: 10.1038/ncomms7037 (2015).

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