Although the Dmanisi jaw and its significance were largely overshadowed in 1991, excavations continued. In the summer of 1999, David Lordkipanidze sent word that there was something new and special from Dmanisi: "Skulls," he said enigmatically. We waited eagerly for more information. In May of 2000, a wonderful new paper appeared in Science by Gabunia and a host of colleagues, including Justus, Lordkipanidze and the German researchers who had worked with them from the beginning. Enlarging the team were two Americans—Carl Swisher III, a dating specialist, and Susan Antón, an expert on the skull of Homo erectus—and Marie-Antoinette de Lumley, a renowned archaeologist from the Laboratoire Museum National d'Histoire Naturelle.
Skulls it was. The paper announced two new skulls of Homo erectus from Dmanisi, one very complete and the other a partial skull missing the face. Anatomically, these specimens were very similar to the older, African specimens like Nariokotome, which the Dmanisi team called Homo ergaster, meaning that ergaster was no longer a strictly African form. The antiquity of Dmanisi was now firmly established at 1.7 million years, based on state-of-the-art radiometric and paleomagnetic studies by Swisher and colleagues; the date was supported by additional study of the faunal material. Finally, more than 1,000 stone artifacts excavated from Dmanisi confirmed that the tools were part of the Oldowan (or Mode I) culture.
This time, the new Dmanisi discoveries were widely hailed by the media who garnered many catchy quotes from major figures in paleoanthropology. "Fossil signs of first human migration are found," The New York Times cheered. "This has doubled again the age of humans in Europe, or at least at the gates of Europe," declared Giacomo Giacobini of the University of Turin, echoing an endorsement by Ofer Bar-Yosef of Harvard University, who has visited Dmanisi. "As soon as Homo erectus evolves in Africa, they're out," remarked Walker to a reporter. Ian Tattersall of the American Museum of Natural History added, "these guys [were] moving very, very fast." The million-year time lag simply evaporated, leaving in its place an impressively rapid outward dispersal from Africa.
Why are the claims for Dmanisi accepted now, when they were not in 1991? For one thing, the evidence itself is stronger. Skulls are more readily identifiable to species than are jaws when hominids are at issue. Bringing new experts onto the team, well known for their work in dating, morphology and archaeology, has also enhanced the credibility of the work.
Since 1991 the field's focus has shifted. The move to eliminate Homo erectus is largely defunct, and many anthropologists use Homo ergaster as an informal shorthand for "the earliest part of the evolving ergaster/erectus lineage." Moreover, the simple dichotomy that once linked early Africa-Oldowan and contrasted that complex with the late Eurasian-Acheulian has been dismantled. In 1994, Carl Swisher and colleagues produced evidence that the Javan Homo erectus sites may range in age from as much as 1.8 million years to roughly 50,000 years, making them both younger and older than previously thought. Scrappy fossils that may be Homo erectus have been found in China, too, dating to about 1.9 million years. Thus, "early" no longer implies "African." Similarly, though Oldowan tools once suggested great antiquity, they too have been found at younger sites, such as Gran Dolina at Atapuerca, Spain, some 780,000 years ago, whereas the oldest Acheulian sites in Eurasia are now as old as 1.5 million years. A whole series of finds and analyses has contributed to a new paradigm that makes the Dmanisi finds more palatable.
This episode offers an important lesson about how science is done. When we scrutinize a colleague's work, we try to make an objective judgment. We evaluate the work against the holy grails of Replicability and Causality, but these are largely unattainable goals, at least for those working with fossils. Like most scientists, we tend to accord an extra dollop of credibility to studies conducted by colleagues known to have done reputable work.
But should the work of the young or the less known be held to higher standards than that of the great matriarchs and silverbacked males of the field? Skepticism is a cheap stance to adopt, for it is easier to cast doubt than to substantiate, especially if new techniques and new paradigms must be forged along the way. Science is a process of discovery, not confirmation. Let us allow for the occasional, delicious surprise that makes us rethink all we thought we knew.
© Pat Shipman
© Pat Shipman