Dmanisi Homo erectus Fossil Count Grows
More bones matching the skulls from the purported Eurasian Homo erectus skulls in Dmanisi, Republic of Georgia have been found (for background, see 08/31/2005 bullet 5, 03/20/2005, 08/01/2002, 11/29/2002). The find was reported in Nature1 with commentary by Daniel Lieberman in the same issue.2
The bones, including ribs, leg bones and arm bones, fingers and clavicles came from three adults and one adolescent. These specimens continue to arouse controversy. The individuals were apparently small in stature yet had modern characteristics; Lieberman wrote, “The adult’s limb proportions are quite modern, with a relatively long femur compared with the humerus, and a tibia/femur ratio similar to that of modern humans from Europe.” The foot bones also showed a prominent arch. Other parts, like the shoulder, body size and brain-to-body ratio appeared “primitive” to the discoverers. The mixture of modern and primitive trait was puzzling. The original paper described these traits:
This material shows that the postcranial anatomy of the Dmanisi hominins has a surprising mosaic of primitive and derived [i.e., modern] features. The primitive features include a small body size, a low encephalization quotient and absence of humeral torsion; the derived features include modern-human-like body proportions and lower limb morphology indicative of the capability for long-distance travel.
This “mosaic” pattern led them to conclude, “Thus, the earliest known hominins to have lived outside of Africa in the temperate zones of Eurasia did not yet display the full set of derived skeletal features.” Yet deciding what is primitive and what is modern is not an exact science. These specimens show surprising variability within the Homo erectus group. One problem with these specimens is their age: they appeared in Eurasia half a million years earlier (1.8 Mya) than the accepted out-of-Africa hypothesis thought. Another problem is that they don’t look like what paleoanthropologists expected from the African examples. A third problem is that since Homo habilis has been found overlapping in age with Homo erectus, the old story of progression has been called into question (09/01/2007, 08/09/2007). Lieberman stirred these problems around:
When viewed up close, however, the Australopithecus�Homo transition has always been murky. One problem is that we don’t know enough about Homo habilis, the putative ancestor of H. erectus. In addition, early H. erectus fossils are quite variable, and the more we look, the more we find contrasts with later hominins (the formal term for a species in the human lineage). For example, their rate of development was rapid and chimp-like, rather than slow and extended as in modern humans. Also, brain size relative to body size in the earliest H. erectus fossils is not much different from that of many australopiths or H. habilis. Finally, the earliest non-African fossils of Homo from Dmanisi, Georgia, which are dated to 1.77 million years ago, resemble H. erectus in many respects. But they are highly variable, and more in the size range of H. habilis than of H. erectus.
With data this murky, a reporter could pick any angle to focus on. That’s what happened in news reports about this find. Some, like National Geographic, BBC News and Live Science, celebrated the transitional-form interpretation, while others, like PhysOrg, focused on the questions these puzzling bones raise for researchers. News@Nature, by contrast, primarily celebrated the luck of finding this treasure trove, then cautioned, “Even though this sample provides a good look at H. erectus in this time and place, experts caution against drawing broad conclusions about H. erectus.”
Speaking of variability, geneticists are also finding unexpected variation in the human genome. When Craig Venter had his own genome sequence published earlier this month (see Yahoo News), geneticists were surprised at the number of differences between his and the “standard” genome that came out of the Human Genome Project. Yet clearly both data sets represented completely modern humans. Given the obvious differences between Tom Thumb and Robert Wadlow, and between skinny models and sumo wrestlers, at what point does human variability put someone outside the category Homo sapiens? (see 07/22/2007). If one cannot know this from genes when we have the live specimens to talk to, how much can be ascertained from bones or salvaged DNA, when the flesh is long gone?
1Lordkipanidze et al, “Postcranial evidence from early Homo from Dmanisi, Georgia,” Nature 449, 305-310 (20 September 2007) | doi:10.1038/nature06134.
2Daniel Lieberman, “Palaeoanthropology: Homing in on early Homo,” Nature 449, 291-292 (20 September 2007) | doi:10.1038/449291a.
Why don’t news reporters listen to the caution about drawing broad conclusions? The reporters do it all the time, and yet the scientists never stop them. In fact, when they talk to the reporters, they often lose all scientific restraint and tell stories like the worst of them.
Update: Now they’re at it again: while this entry was being prepared, another report came out claiming that Hobbit Man must have been non-human because the wrist bones are slightly different. The usual suspects, like LiveScience and the BBC News, never learn. Haven’t they seen small people before? Rather than consider variability and the effects of disease or genetic isolation, they are pushing the primitive-to-modern human-ancestry myth again.
Read the original paper and you will find it is a confusing mishmash of conflicting data. They can’t decide whether these specimens were primitive, modern, or transitional. Remember the guy in 2002 (08/01/2002) who was so puzzled by Dmanisi man, he suggested putting the bones back in the ground? Why would the Dmanisi people have modern arches and walk like modern people, if they were less than human? Does evolution put out certain fully modern traits in advance of others? Was the Dmanisi tribe trying to walk out of Africa to go shopping for bigger brains, and if so, how could they do it without the brains in the first place? Science Daily said that hominids were able to walk just as well as modern humans 3.5 million years ago. Then, certainly they could have been physically agile to hunt down the potatoes that gave them big brains (09/11/2007). And now that we know that so-called Homo habilis couldn’t be an ancestor, why doesn’t anyone draw the conclusion that the whole mishmash of evolution stories is pure fiction?
The more logical conclusion is that there is more variability in the human body than previously thought. Most thinking people realize mosaics are an art form. Only one-dimensional Darwinian thinking tries to rearrange the pieces of a mosaic into a straight line.