Are the “hobbits” a separate prehuman species?

The 2004 “hobbit” discovery and controversy

In 2004 the scientific world was startled by the announcement of the discovery of Homo floresiensis, more commonly known as the “hobbit” due to its diminutive size, on the island of Flores in the Indian Ocean north of Australia. Remarkably, this specimen lived until as recently as 66,000 years ago [Wade2004] (originally it was thought that they lived until 18,000 years ago, but this was later corrected). The discoverers pointed out that the fossil combined an unusual mix of human and early hominid features, including a nearly complete skull that most resembled Homo erectus, but with legs more akin to Australopithecines. The authors theorized that the specimen represented a distinct species of hominins, and its diminutive size was due to an effect known as “island dwarfism” (the evolutionary reduction in size of a species confined to an island or other domain with limited resources).

A heated and rather public controversy ensued [Krause2009]. The initial salvo was from biologists Maciej Hennenberg and Alan Thorne, who dismissed the notion of a separate species, saying that the small skull instead represented merely a case of microcephaly, a malady that causes dwarfism in afflicted humans. In response, Brown and Morwood acerbically described Henneberg and Thorne’s article as “an extremely poorly informed, and ill designed, piece of ‘research’.” The microcephaly explanation was then boosted by a paper published by Indonesian researcher Teuku Jacob in the prestigious National Academy of Science, after a detailed comparison of the hobbit bones with the skeletal features of regional humans. What’s more, Robert Martin of the Field Museum of Natural History in Chicago published a paper drawing into question the initial claim that the Hobbits had descended from Homo erectus.

But then Dean Falk, a leading expert on hominid brain evolution at Florida State University, compared Flores casts with molds made from the braincases of several great apes, an Australopithecus, a Homo erectus, an average-sized Homo sapiens, a pygmy, and a microcephalic Homo sapiens. She found that although the Flores find closely resembled Australopithecine africanus (a hominin species that lived 2-3 million years ago) in terms of relative brain-to-body size, its brain’s general shape was most similar to that of Homo erectus. Falk also observed that the Flores specimen’s cast bore little likeness to that of the pygmy and was least similar, among the various candidates, to microcephalic humans.

Subsequently additional hobbit skeletons were found, casting more doubt on the microcephaly alternative explanation. Some published studies concluded that the tools found on Flores were quite similar to those of Homo erectus, but others said they were more similar to apes and australopithecines. Still other studies analyzed the feet of the specimen, and additional studies were published on the cranium. Critics of the new species designation have asserted that there are numerous other pathologies that need to be examined. For example, a 2010 study noted similarities between anatomical features of the Flores specimens and persons afflicted with hypothyroid cretinism (iodine deficiency) [Oxnard2010]. Numerous other studies have been done, with researchers aligning on one side of the debate or the other.

The latest results

In November 2015, Japanese researchers found, after a thorough analysis of hobbit teeth, that the specimens had numerous dental traits not typical of any human (or any other known hominin), but relatively close to those of Homo erectus, thus supporting the original hypothesis that the hobbits represent a distinct branch of the hominin family tree [Choi2015]. This was followed in April 2016 by a team led by Canadian paleoanthropologist Matthew Tocheri, who more carefully studied the cave in which the fossils were found. These researchers found, by carefully dating ash in the cave and the hobbit fossils themselves, that the hobbits lived from 66,000 to 87,000 years ago, not 18,000 as originally claimed, which rules out the possibility that these are human (since humans did not arrive on the island until 50,000 years ago) [Gramling2016]. Then in June 2016, Australian researchers announced the discovery of additional Homo floresiensis fossils, some as old as 700,000 years, further establishing that these were a distinct lineage [Zimmer2016a]. Thus while some researchers are still unconvinced, the tide is turning strongly to the original hypothesis that the hobbits are a separate hominin species, although quite clearly not ancestral to the human branch of the family tree.

Other recent discoveries

The hobbit discovery, together with the emerging consensus that these specimens represent a distinct hominin lineage, is just one of several recent discoveries, including the following:

  • New “Homo naledi” fossils in South Africa. In September 2015, a research team led by Lee Burger, who had previously discovered the Australopithecus sediba fossils, announced that they have uncovered a treasure-trove of fossils from a new hominin species, which they have named “Homo naledi.” To date they have catalogued 1,550 individual fossil elements, which is by far the largest number of hominin fossil fragments ever found at a single site. These fossil elements represent parts of at least 15 individuals, and some of these skeletons are nearly complete. This amazing find is in stark contrast to most hominin fossil finds, where little more than a handful of isolated fragments from a single individual are identified. The researchers are as mystified as anyone as to how and why these human remains were placed in this remote chamber of the cave, which required extra-slim investigators (all of them women) to reach. Although precise radiometric dates are not yet available, the researchers estimate the ages as 2-3 million years. This places the fossils as more recent than most Australopithecus species, but more ancient than known Homo species [Wilford2015b].
  • Complete Neanderthal genome from a toe bone. In December 2013, a team of researchers led by Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany announced that they had extracted the entire genome of a 130,000-year-old Neanderthal from a single toe bone found in a cave in Siberia. This data, together with other recent studies, has established that humans, Denisovans (see next item) and Neanderthals represent three different branches on a common tree that diverged roughly 600,000 years ago, but that there has been significant genetic sharing through interbreeding since then [Zimmer2013c].
  • Denisovan fossils. In March 2010, Paabo and his team announced the discovery of a new branch of hominin, identified as the result of analyzing mitochondrial DNA (mtDNA) from a finger bone found in the Denisova region of Siberia. This species co-existed with humans until as recently as 50,000 years ago, yet is roughly twice as distant (measured in terms of the time since a common ancestor) from modern humans as Neanderthals [Wong2010a]. A follow-up study published in December 2010, based on an entire genome sequence of the specimen, found that not only do the Denisovans represent a “sister” species to Neanderthals, but that in fact this race of prehumans evidently interbred with Southeast Asian humans, since the genomes of modern-day New Guinea natives contain 4.8% Denisovan DNA [Zimmer2010a]. What’s more, an additional study published in August 2011 noted that interbreeding with Neanderthals and Denisovans actually boosted human immunity to viruses [McGrath2011].
  • Oldest prehuman DNA. In a surprising new development, announced in December 2013, researchers at the Max Planck Institute retrieved DNA from an ancient hominin fossil 400,000 years old found in Spain. It is easily the oldest specimen ever to have its DNA analyzed. These researchers had expected the specimen to be a forerunner of Neanderthals, but its DNA more closely resembles that of the Denisovan lineage, mentioned above. This raises the possibility that the Spanish specimen might belong to yet another branch of ancient prehumans, or even the remnant of Homo Erectus, which originated roughly 1.8 million years ago but was thought to be extinct more recently [Zimmer2013b].

Two “family tree” diagrams of these and many other specimens are given at Prehuman fossils.

Conclusion

In summary, there is no truth to the claim by creationists and others that there are huge gaps (i.e., “missing links”) between ancient apes and humans. If anything, there is an embarrassment of riches. So many specimens have been found in the past decade or two that the only challenge is determining which are distinct species and which are simply varieties of a single species, and which are truly in the direct line that leads to modern humans and which are evolutionary dead ends.

In addition, the controversies that have raged rather publicly in this arena also demolish claims that there is a “conspiracy” or “group-think” among scientists. To the contrary, when one peers beneath the smooth public veneer of the world of scientific research, one finds, more often than not, heated debates and disagreements, particularly at the forefront of research where genuine issues remain unresolved. Indeed, it is utterly absurd to think that a “conspiracy” or “group-think” could persist more than momentarily in a worldwide community of hundreds of thousands of professional scientists, representing many different nations, cultures and religious traditions, who competitively critique each other’s work in scientific journals and conferences, and who evaluate each other’s research proposals in highly competitive bids for government funding.

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