The Flores find :: more thoughts on Liang Bua

I (and others) have had about a week to reflect on this new skeleton and its significance. There is little question that this is one of the most vexing discoveries ever.

To understand why, compare the situation with that surrounding a major find like Lucy (AL 288-1). Lucy (and the Hadar sample as a whole) presented little new or interesting information about the morphology of australopithecines. The Sterkfontein sample, which had emerged over the thirty years prior to the Hadar discoveries, demonstrated nearly everything important about the australopithecine adaptive pattern--including body size, dental characteristics, evidence for bipedality, and brain size. The story from Hadar was that it was older than everything else then known, and that there was a relatively complete skeleton that associated much of the important morphology into a single specimen. This is why Lucy now has such importance in our textbooks, but the fact is that almost everything interesting was known long before.

One might say some of the same things about Liang Bua. It looks in many respects like we know some early hominids looked (although admittedly with many differences in detail). But here the differences in time and place are a much greater story, because they upset so much more. A "new earliest hominid" does little but push back the date of hominid origins, especially since none of the "new earliests" have been particularly informative about the ancestral condition (they are all obligate bipeds so far, and none of them is very chimpanzee-like, notwithstanding the dentition of Ardipithecus). But Liang Bua is striking because it has no obvious ancestor. If it is an australopithecine, where are the earlier Asian australopithecines that it descends from? Meganthropus? If it descended from early Javan humans like Sangiran, then what accounts for the necessary selection for smaller brains leading to this specimen?

Only if LB1 can be attributed to pathology are these questions less pressing. In that case, it represents just one of (potentially) many human populations that lived on Flores or passed through it on the way to Sahul, Melanesia, and points east. The pathology hypothesis has not yet been refuted, and it is important to keep that in mind.

Do the tools belong to LB1 or its ilk?

With a 380 mL brain, LB1 is at the bottom of the range of australopithecine brain sizes. After the advent of stone tools 2.6 million years ago, no known hominid has a brain size of less than 400 mL, and most paleoanthropologists have assumed that the manufacture of stone was accomplished by species with brain sizes that averaged 500 mL or more. It is not at all clear to what extent the mass of neural tissue is related to tool manufacture or any other capabilities. Perhaps it is the case that the essential changes affected the structure of the brain rather than its size, and a smaller brain might well have the circuitry to accomplish many advanced cognitive tasks. It is certainly true that chimpanzees are capable of tool use, the mastery of rudimentary symbol manipulation, and cooperative foraging, despite having brains that average 400 mL or less.

On the other hand, modern humans reached Australia by 50,000 years ago, and were present in island Melanesia by 30,000 years ago. The route to both of these places passes through Flores, so it is highly probable that modern humans were present on Flores 18,000 years ago, when the LB1 lived.

In this context, I think we can reasonably assume that the stone tools, fire, and evidence of Stegodon hunting can be attributed to these modern people. Colin Groves has sent me a reference to an ABC News story where he makes much the same argument.

This leaves the two main hypotheses about LB1:

  1. it was a pathological member of this modern human population
  2. it was part of an earlier hominid population alongside these modern humans

In the second case, we can speculate about the relationship of these populations. Perhaps LB1 was a victim of the modern humans: i.e. it is in the cave for the same reason the Stegodon remains are in the cave. Perhaps the tiny-bodied population avoided the modern humans in the same way as today orangutans avoid modern people on Borneo and Sumatra. This might imply a very different ecological role for these smaller hominids, considering the ecological breadth and travel potential of the modern humans alongside them.