A Very Big Surprise from a Very Little Hominid
Abundant fossil evidence from several regions shows that by 25,000 years ago, modern humans had dispersed to all major areas of the Old World, and they would soon journey to the New World as well. But at about the same time, there were still remnant populations of earlier hominids surviving in a few remote and isolated corners. We know, for example, that populations of Homo erectus in Java managed to survive on this island long after their cousins had disappeared from other areas (e.g., China and East Africa). Moreover, even though they persisted well into the Upper Pleistocene, physically these Javanese hominids were still very similar to other H. erectus. However, other populations apparently branched off from some of these remnant Indonesian H. erectus groups and either intentionally or accidentally found their way to other, smaller islands to the east. Here, under even more extreme isolation pressures, they evolved in an astonishing direction. In late 2004, the world awoke to the startling announcement of an extremely small-bodied and small-brained hominid discovered on the island of Flores, east of Java (see Fig. 1). The remains consist of an incomplete skeleton of an adult female and additional pieces from six other individuals. The female skeleton is remarkable in several ways (Fig. 2). First, she stood barely 3 feet tall (as short as the smallest australopithecine), and her brain (estimated at a mere 400 cm3) was no larger than that of a chimpanzee (Brown et al., 2004) nor any larger than Australopithecus afarensis (Falk et al., 2005). And perhaps most startling of all, these extraordinary hominids were still living on Flores as recently as 14,000 years ago (Morwood et al., 2004)!
Where did they come from? As we said, their predecessors were probably H. erectus populations like those found on Java. How they got to Flores (some 400 miles away, a portion of which is over open ocean) is a mystery. There are several connecting islands, and to get between them, these hominids may have drifted across on rafts; but there’s no way to be sure of this. How did they get to be so physically different from all other known hominids? Here we are a little more certain of the answer. Isolated island populations can quite rapidly diverge from their relatives elsewhere—as we noted regarding the famous Galápagos finches observed by Darwin. A frequent consequence seen among such isolated animals involves natural selection favoring reduced body size. For example, there are populations of dwarf elephants found on islands in the Mediterranean as well as on some channel islands off the coast of southern California. And perhaps most interesting of all, dwarf elephants also evolved on Flores (found in the same beds with the little hominids). The evolutionary mechanism thought to explain such dwarfing in both the elephants and the hominids is an adaptation to a reduced amount of resources, leading through selection to smaller body size. Other than short stature, what did the Flores hominids look like? In terms of thickness of cranial bone, dentition, and most especially cranial shape and reconstructions of brain shape, they most resemble Homo erectus. Nevertheless, even when scaling for small body size, their brains are still much smaller than any H. erectus individual (Falk et al. 2005). In addition to the surprisingly small brain, there are derived features that also set them apart from other hominids. Thus, they have been placed in a separate species, Homo floresiensis. Some critics have raised doubts whether the Flores hominids (especially the nearly complete cranium) are actually a new species, but represent instead a congenital pathology called microcephaly (While widely-publicized, these assertions have not yet been published in a peer-reviewed scientific journal and are thus of marginal scientific validity; see Dalton, 2005 for discussion). Such a rare condition would be most improbable in ancient hominid samples, but even more devastating to the notion the adult H. floresiensis cranium was microcephalic comes from detailed three-dimensional imaging of brain shape and structure, creating what can be called a “virtual endocast” (Falk et al., 2005). As noted, cranial shape resembles that of H. erectus, and it clearly is not a pathologically small (“microcephalic”) H. sapiens. It is truly different from anything found before. What became of the Flores hominids, and could some still be out there somewhere? They were extremely divergent and probably specialized as well. Not long after 14,000 y.a., modern humans reached Flores, and it seems their arrival spelled the doom for H. floresiensis. They seem to have perished quickly, leaving no descendants. It’s very unlikely that anything like these strange hominids survived anywhere much after 10,000 years ago. Currently, with more than 6 billion modern humans inhabiting every corner of the planet, devouring resources as we go, the likelihood of finding any living “archaic” hominid (Yeti, bigfoot, or an H. floresiensis hominid) is extraordinarily slight. Sources: Brown, P., T. Sutikna, M.K. Morwood, et al. 2004. “A New Small-Bodied Hominin from the Late Pleistocene of Flores, Indonesia.” Nature, 431:1055-161.Dalton, Rex. 2005. “Looking for the Ancestors.” Nature, 434:432-434. Falk, Dean, Charles Hildebolt, Kirk Smith et al. 2005. “The Brain of LB1, Homo floresiensis.” Science, 308:242-245.Morwood, M.J., R.P. Suejuno, R.G. Roberts, et al. 2004, “Archeology and Age of a New Hominin from Flores in Eastern Indonesia.” Nature, 431:1087-1091.
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