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paleoanthropology, genetics and evolution

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Looking at Luzon hominins, from the perspective of 1985

In light of this week’s paper by Ingicco and colleagues showing evidence of 700,000-year-old human activity from Kalinga, on Luzon, I’ve been doing a little reading.

I found an interesting article by Lawrence Heaney, published in the 1985 volume of Modern Quaternary Research in Southeast Asia. The title is: “Zoogeographic evidence for Middle and Late Pleistocene landbridges to the Philippine Islands”. In case you wonder about the title, the article shows that there were no land bridges to the Philippines, although there were several ancient land bridges connecting various islands within the Philippines.

The part worth quoting at length has to do with speculations that Homo erectus may have reached the Philippines.

Comments on Homo erectus and land bridges
Given the strong evidence against land bridges from Asia to the Philippines, what does this tell us about the probability of finding Homo erectus in the Philippines?
First, it must be recognized that this analysis has been general; it has not dealt with any specific species, and does not prove that a single species cannot behave in a different fashion from most or all others. The fact that a single species of monkey, Macaca fascicularis, is now recognized to occur in much of Southeast Asia including nearly all of the Philippines, could be taken as evidence that it is possible, however unlikely, that Homo erectus had a similar distribution.
However, it must also be recognized that if Homo erectus did occur on Luzon, for example, they arrived there by crossing over several sea channels that were over 10 km wide, and could have been over 25 km wide. It is possible to imagine a small population of monkeys floating accidentally out to sea on a mass of trees and branches and being rafted to an island 25 km away; it is far, far more difficult to imagine a similar thing happening to a group of proto-humans. Thus, I suggest that if Homo erectus did occur on Luzon, they arrived by deliberate construction of rafts and dispersal across sea channels.

The chapter goes on to consider whether any evidence about Homo erectus on Java suggested that they might have crossed water to islands. This discussion is a bit outmoded from today’s perspective: Although it has long been known that Java was connected to the Asian mainland during the Late Pleistocene, it was not always so evident that all of Java had such connections during the Early Pleistocene, since the island has coalesced as a result of Pliocene and Early Pleistocene uplift and volcanism. So some authors had suggested that the earliest evidence of Homo erectus on Java might have occurred before Trinil was part of the Asian landmass, for example.

More relevant today is that we now know that hominins occupied Flores, Sulawesi, and now Luzon, all prior to 100,000 years ago. Flores and Luzon were peopled during the early Middle Pleistocene.

What’s more, the Flores hominins may represent a hominin group that diverged earlier than the last common ancestor of Homo erectus and archaic and modern humans. This is not a question of Homo erectus dispersing to islands, it may be a question of a branch of hominins that–except for H. floresiensis–is presently unknown.