A very large tooth, not quite human

Daja vu in the news.

Back in March a substantial press surge greeted news in Nature that a finger bone from the Denisova cave in Siberia appeared to be as young as 30,000 years old, definitely from a hominin, probably pre-adolescent and, being hominin, justifiably called a child. But it was, they said then,  neither typical Neanderthal nor Homo sapiens. Preliminary DNA analysis plus bone morphology said as much. See previous post for more on that.

A second shoe dropped, again at Nature,  this week when much the same team, including noted paleoanthropologist Svante Pääbo, reported that further testing shows the bone came from a young girl. Not only that, the nearly-complete genome now at hand suggests  it carried a few genes that can also be found today in some modern members of the Malanesian ethnogeographic group. Its traditional homeland is on some  far-western Pacific islands such as New Guinea. A very large molar from the same cave, from a young adult, further adds to evidence of a different species from us, and that this new one was more closely related to Neanderthals while still distinct from them (and us for sure). The tooth is larger not only than any of yours, but of known Neanderthal specimens too.

And they have a name for the new species, although not a formal Linnean one: the Denisovans. That’s in keeping with Neanderthals, for the valley where their first remains under the light of science.

Last time around, I practically foamed at the mouth at the number of reporters whose writing went faster than their brains and who promptly dubbed the cave’s bone as marking discovery of a new human ancestor. Relative yes, but ancestor no – no more than your uncle Tom is also a direct ancestor (unless, you know, he and your mom or, gad and never mind  …. ). Now it gets complicated on whether to call these things “human ancestors.” They left a genetic trace, via interbreeding, that can still be found in one distinct population of traditional but modern people, but not the rest of us. So it was not part of my ancestral lineage. But it may be a small part of, say,  the deep family tree of Iolu Abil, President of Vanuatu, a lovely archipelago nation northeast of Australia. Most certainly it is not ancestral to the origination of H. sapiens back in southern Africa or wherever that happened 100,000+ years ago. Hmmm. Maybe phylogeny has terms to suit this kind of intermixed gene flow between species in which neither is ancestral to the other.

Some headlines also present the news as though the huge coverage back in March never happened – proclaiming discovery of a recent, new member of our extended family of species. Stories themselves tend to get it straight. Not all, however.

Stories:

• NPR – Joe Palca: Ancient Bone’s DNA Suggests New Human Ancestors ; Savvy piece ties this news to other recent bits of paleo-DNA wizardry, such as other recent news dissecting a Neanderthal site’d DNA as providing evidence for a family and giving insight into the mating patterns among groups of that species. He pronounces the Siberian cave name, presumably correctly:  deNEESova, leading to deNEESovans for its residents, not the deniSOVA I’ve been imagining.  However he treats the news from Denisova Cave as entirely fresh. NPR colleague Christopher Joyce reported the first burst in March.
• AP – Malcolm Ritter : DNA says new human realtive roamed widely in Asia ; Makes clear the essential discovery was announced already (Ritter covered that one too), evades calling these creatures human ancestors in the full sense of the term, and reports that no new species name has been assigned to the Denisovans because it’s not yet clear whether they represent full species, or perhaps a Neanderthal sub-species or similar close relation, or perhaps even an extinct species already named from other fossils.
• Reuters – Maggie Fox: Gene study shows Neanderthals had eastern cousins; Fox declares it a new species, period. Also a sister group to Neanderthals. Unsure what that means. She gets in the interbreeding, characterized as a dalliance between modern humans and Denisovans somewhere in Asia.
• NYTimes – Carl Zimmer: Siberian Fossils Were Neanderthals’ Eastern Cousins ; Zimmer composes a story, a tale with narrative muscle, tracing how this latest paper came to be and the dynamics of its authorship. Very nice. He fits the tooth’s morphology in as a clinching piece of evidence even though the DNA was almost all from the insides of the finger bone. The journal paper makes much of the genetic bottleneck evidence in Neanderthal DNA, but not in Denisovans, hinting that the former were a genetically depauperate line while the Denisovans had split away earlier and, to the east, maintained sturdier genetic underpinning. Zimmer misses that bit of implied drama. Even Zimmer can’t get in everything.
• Telegraph: Ancient cousin of humans identified by scientists ;   Jumbled at the top, gets its legs toward the end, but is among the accounts that seem oblivious to earlier announcement of the essential discovery. No byline. Sheer rewrite, without attribution, one supposes. The lively quotes toward the end appear all to be from a UC Santa Cruz press release (in Grist below).
• National Geographic – Ker Than: New Type of Ancient Human Found – Descendants Live Today? ; That’s a hed with the news, and excitement. This, like Zimmer’s in NYTimes, is a solid yarn by a reporter who sees the larger picture and composes a story. He even gets one expert noting the fuzziness of the term species.
• The Australian- Amos Aikman : Meet the Denisovans, indigenous Australia’s Siberian kin ; It’s a stretch, but only a small one, to include Australia’s aborigines as carriers of a few Denisovan genes. A source tells Aikman they and Melanesians are part of a larger clade within H. sapiens, so it’s plausible. Time will tell, and probably soon. One imagines the Max Planck-Harvard gang is already running pertinent tests.
• Sydney Morning Herald: Deborah Smith: Giving accepted prehistoric history the finger – DNA tests reveal new group of ancestors ; Again, the group declaration was made a while ago, this report fills in important detail. She treats it as all new. But she does have a hint of detail nobody focusses on – the modern human migration that picked up Neanderthal genes soon after leaving Africa continued on through Asia, where one column got intimate with a few Denisovans. Ergo, the people of New Guinea and nearby regions may be the world’s only ones with traces of both encounters.
• BBC – Pallob Ghosh:  Ancient human species ‘interbred with us’ ;  The pic with this illustrates the two interbreeding episodes, earlier by Neanderthals, later by their offshoots the Denisovans. Plus in a news clip paleoanthropologist Chris Stringer on this news’s context.
• USA today – Dan Vergano: New extinct species of pre-humans confirmed ; Short, and correct as far as I can tell.
• NatureNews – Ewen Callaway: Fossil genome reveals ancestral link/ A distant cousin raises questions about human origins ; Insider Callaway had, of course, plenty of time and access advantages over other scriveners. Nice job, but the hed’s declaration that this raises questions in not quite backed up. More like it refines the focus, revealing surprises.

*UPDATE: At USA Today, Dan Vergano gathered expert reactions to the news, with considerable analysis and quoted at length, to this news (see comment).

There are more, and perhaps I’ll get a chance to update this with more, substantial stories.

One does wonder – remember the big battles of a decade or two ago on how to envision the rise of modern mankind? On one side were partisans of the pure “Out of Africa” scenario, sometimes called African Eve, spawned by the  DNA work of Allan Wilson and colleagues at UC Berkeley in the early 90s. It posited a single-origin and total replacement story for H. sapiens‘s start and spread. On the other side: the “Regional Hypothesis” pushed by Milford Wolpoff of the University of Michigan. It supposed a diffuse, nearly simultaneous rise of H. sapiens across the breadth of the Old World via evolution and gene flow among the likes of H. erectus and Neanderthals. Maybe a compromise has been offered by reality. Somebody call Wolpoff, if he’s taking calls, and find out if a truce is in the works.

Grist for the Mill:

Max Planck Society Press Release ; Harvard Med. Sch. Press Release ;  UC Santa Cruz Press Release ;

- Charlie Petit

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