It's the end-of-semester crunch for many of us in the academic world. My Facebook feed is filled with posts by people who been grading for too long and finding too many cases of student plagiarism. The end of my road was easy this semester, as I taught a very pleasant field school populated by a good group of students. Having taught a 4/4 one year, I feel for all of you still slogging away.
I wanted to take a minute to write about two stories related to claims for sites of Middle Pleistocene age in two different corners of the world. Unless you're grading papers in a lead-lined underground bunker, you heard about the claim for a 130,000-year-old archaeological site in California that was published in Nature yesterday. That's the first one. The second one involves an age estimate of 250,000 for the Homo naledi remains first described in September of 2015. The first claim is buzz-worthy because of its extreme earliness (a good 115,000 years prior to what most archaeologists accept as good evidence for human entry into the Americas). The second claim is surprising for its lateness. Let's do the second one first.
Homo naledi is Only 250,000 Years Old?
The announcement of Homo naledi and the results of the Rising Star Expedition made a huge splash in the fall of 2015 (I gave my take on it here). One of the main unresolved issues at the time of the initial announcement was that the remains were not dated. The lack of an age estimate made it difficult to frame the analysis in terms of evolutionary relationships with other hominins and the implications of the claims that Homo naledi was burying its dead. If the remains are very early (say, close to 2 million years old . . . ), the claims for organized mortuary behavior are spectacular. If they're very late, the mosaic of primitive and derived features becomes very curious.
Two days ago, the New Scientist ran a story titled "Homo naledi is Only 250,000 Years Old -- Here's Why that Matters." Here is a quote from that piece:
"Today, news broke that Berger’s team has finally found a way to date the fossils. In an interview published by National Geographic magazine, Berger revealed that the H. naledi fossils are between 300,000 and 200,000 years old.
“This is astonishingly young for a species that still displays primitive characteristics found in fossils about 2 million years old, such as the small brain size, curved fingers, and form of the shoulder, trunk and hip joint,” says Chris Stringer at the Natural History Museum in London."
I wanted to take a minute to write about two stories related to claims for sites of Middle Pleistocene age in two different corners of the world. Unless you're grading papers in a lead-lined underground bunker, you heard about the claim for a 130,000-year-old archaeological site in California that was published in Nature yesterday. That's the first one. The second one involves an age estimate of 250,000 for the Homo naledi remains first described in September of 2015. The first claim is buzz-worthy because of its extreme earliness (a good 115,000 years prior to what most archaeologists accept as good evidence for human entry into the Americas). The second claim is surprising for its lateness. Let's do the second one first.
Homo naledi is Only 250,000 Years Old?
The announcement of Homo naledi and the results of the Rising Star Expedition made a huge splash in the fall of 2015 (I gave my take on it here). One of the main unresolved issues at the time of the initial announcement was that the remains were not dated. The lack of an age estimate made it difficult to frame the analysis in terms of evolutionary relationships with other hominins and the implications of the claims that Homo naledi was burying its dead. If the remains are very early (say, close to 2 million years old . . . ), the claims for organized mortuary behavior are spectacular. If they're very late, the mosaic of primitive and derived features becomes very curious.
Two days ago, the New Scientist ran a story titled "Homo naledi is Only 250,000 Years Old -- Here's Why that Matters." Here is a quote from that piece:
"Today, news broke that Berger’s team has finally found a way to date the fossils. In an interview published by National Geographic magazine, Berger revealed that the H. naledi fossils are between 300,000 and 200,000 years old.
“This is astonishingly young for a species that still displays primitive characteristics found in fossils about 2 million years old, such as the small brain size, curved fingers, and form of the shoulder, trunk and hip joint,” says Chris Stringer at the Natural History Museum in London."
If you click on the link to the interview in National Geographic, you'll find that it leads to a photograph of a magazine page posted on Twitter by Colin Wren. I'm unable to access the original piece in National Geographic. I'm not quite sure what is going on, but presumably a formal publication explaining the age estimate is in the works and will be out soon.
A 250,000 year age would, indeed, be surprising. Previous age estimates have ranged widely, from 900,000 years old (based on dental and cranial metrics) to 2.5 to 2.8 million years old (based on overall anatomy). Age estimates based on the anatomical characteristics of the remains are problematic, obviously, as they rely on assumptions about the pattern, direction, and pace of evolutionary change that may not be correct. Hopefully the latest age estimates are independent of the anatomy (i.e., have a geological basis). This blog has some additional background.
A 250,000 year age would, indeed, be surprising. Previous age estimates have ranged widely, from 900,000 years old (based on dental and cranial metrics) to 2.5 to 2.8 million years old (based on overall anatomy). Age estimates based on the anatomical characteristics of the remains are problematic, obviously, as they rely on assumptions about the pattern, direction, and pace of evolutionary change that may not be correct. Hopefully the latest age estimates are independent of the anatomy (i.e., have a geological basis). This blog has some additional background.
And now on to the second one, which concerns . . .
A Middle Pleistocene Occupation of North America?
It's hard to know where to even start with this one. The claim is bold, the journal is prestigious, the popular press has been all over it, and the reaction from professionals has been swift and (as far as I can tell) overwhelmingly negative. The reactions I have seen among my colleagues and friends have been almost universally skeptical, ranging from amusement to mild outrage. I'll just summarize all that with gif I saw in an online discussion about the paper:
A Middle Pleistocene Occupation of North America?
It's hard to know where to even start with this one. The claim is bold, the journal is prestigious, the popular press has been all over it, and the reaction from professionals has been swift and (as far as I can tell) overwhelmingly negative. The reactions I have seen among my colleagues and friends have been almost universally skeptical, ranging from amusement to mild outrage. I'll just summarize all that with gif I saw in an online discussion about the paper:
The claim centers around an assemblage of stones and mastodon bones that the authors interpret as unequivocal evidence of human activity in California at the Middle/Late Pleistocene transition (ca. 130,000 years ago). Here is the first part of the abstract of the Nature paper by Steven Holen and colleagues:
"The earliest dispersal of humans into North America is a contentious subject, and proposed early sites are required to meet the following criteria for acceptance: (1) archaeological evidence is found in a clearly defined and undisturbed geologic context; (2) age is determined by reliable radiometric dating; (3) multiple lines of evidence from interdisciplinary studies provide consistent results; and (4) unquestionable artefacts are found in primary context. Here we describe the Cerutti Mastodon (CM) site, an archaeological site from the early late Pleistocene epoch, where in situ hammerstones and stone anvils occur in spatio-temporal association with fragmentary remains of a single mastodon (Mammut americanum). The CM site contains spiral-fractured bone and molar fragments, indicating that breakage occured while fresh. Several of these fragments also preserve evidence of percussion. The occurrence and distribution of bone, molar and stone refits suggest that breakage occurred at the site of burial. Five large cobbles (hammerstones and anvils) in the CM bone bed display use-wear and impact marks, and are hydraulically anomalous relative to the low-energy context of the enclosing sandy silt stratum. 230Th/U radiometric analysis of multiple bone specimens using diffusion–adsorption–decay dating models indicates a burial date of 130.7 ± 9.4 thousand years ago. These findings confirm the presence of an unidentified species of Homo at the CM site during the last interglacial period (MIS 5e; early late Pleistocene), indicating that humans with manual dexterity and the experiential knowledge to use hammerstones and anvils processed mastodon limb bones for marrow extraction and/or raw material for tool production."
The 130,000 year-old date is way, way, way out there in terms of the accepted timeline for humans in the Americas. Does that mean the conclusions of the study are wrong? Of course not. And, honestly, I don't even necessarily subscribe to the often-invoked axiom that "extraordinary claims require extraordinary evidence." I think ordinary, sound evidence works just fine most of the time when you're operating within a scientific framework. Small facts can kill mighty theories if you phrase your questions in the right way.
So how should we view claims like this one? For this claim to stand up, two main questions have to withstand scrutiny. First, is the material really that old? Second, is the material really evidence of human behavior?
If we accept the age of the remains, we're left with the second question about whether those remains show convincing evidence of human behavior. As you can see from the abstract, the claim for human activity has several components (modification of the bones, the presence and locations of stone cobbles interpreted as tools, etc.). The authors contention (p. 480) is that
So how should we view claims like this one? For this claim to stand up, two main questions have to withstand scrutiny. First, is the material really that old? Second, is the material really evidence of human behavior?
If we accept the age of the remains, we're left with the second question about whether those remains show convincing evidence of human behavior. As you can see from the abstract, the claim for human activity has several components (modification of the bones, the presence and locations of stone cobbles interpreted as tools, etc.). The authors contention (p. 480) is that
"Multiple bone and molar fragments, which show evidence of percussion, together with the presence of an impact notch, and attached and detached cone flakes support the hypothesis that human-induced hammerstone percussion was responsible for the observed breakage. Alternative hypotheses (carnivoran modification, trampling, weathering and fluvial processes) do not adequately explain the observed evidence (Supplementary Information 4). No Pleistocene carnivoran was capable of breaking fresh proboscidean femora at mid-shaft or producing the wide impact notch. The presence of attached and detached cone flakes is indicative of hammerstone percussion, not carnivoran gnawing (Supplementary Information 4). There is no other type of carnivoran bone modification at the CM site, and nor is there bone modification from trampling."
My impression is that most archaeologists are, like me, are skeptical that all other possible explanations for the stone and bone assemblage can be confidently rejected. I'm no expert on paleontology and taphonomy, but as I thought through the suggested scenario, I wondered how all the meat came off the bones before before the purported humans smashed them open with rocks. The authors state that there's no carnivore damage, and unless I missed it I didn't see any discussion of cutmarks left by butchering the carcass with stone tools. So where did the meat go? If it wasn't removed by animals (no carnivore marks) and wasn't removed by humans (no cutmarks) did it just rot away? If so, would the bones have still been "green" for humans to break them open?
The absence of cut marks would be perplexing, as we have direct evidence that hominins have been using using sharp stone tools to butcher animals since at least 3.4 million years ago. The 23,000-year-old human occupation of Bluefish Cave in the Yukon is supported by . . . cutmarks. We know that Neandertals and other Middle Pleistocene humans had sophisticated tool kits that were used to cut both animal and plant materials.
Is it possible that pre-Clovis occupations in this continent extend far back into time? Yes, I think it is. Does this paper convince me that humans messed around with a mastodon carcass in California at the end of the Middle Pleistocene? No, it does not.
The absence of cut marks would be perplexing, as we have direct evidence that hominins have been using using sharp stone tools to butcher animals since at least 3.4 million years ago. The 23,000-year-old human occupation of Bluefish Cave in the Yukon is supported by . . . cutmarks. We know that Neandertals and other Middle Pleistocene humans had sophisticated tool kits that were used to cut both animal and plant materials.
Is it possible that pre-Clovis occupations in this continent extend far back into time? Yes, I think it is. Does this paper convince me that humans messed around with a mastodon carcass in California at the end of the Middle Pleistocene? No, it does not.
Some of my friends seem angry that the paper was published. I have mixed feelings. I'm not at all convinced by what I've read so far, but I think claims like this serve a useful purpose whether or not they turn out to be correct. I can understand the concerns I've heard voiced about unfairness in the standards of evidence and argument that are acceptable at various levels of publication, but I also think there should always be room for making bold claims about the past as long as those claims have some basis in material evidence that can be independently evaluated. It will be interesting to see how the buzz over this paper plays out. Will other professionals carefully examine the remains and offer up their opinions? Will the claim be quickly dismissed and forgotten about?
One thing I can guarantee is that the "fringe" will be on the Cerutti Mastodon like a wet diaper: they've already got a laundry list of "Neanderthal" remains from the New World (some buried in Woodland-age earthen mounds!) and "pre-Flood" sites into which they'll weave this report into. Maybe Bigfoot will even be implicated. Maybe the mastodon was killed by Atlanteans.
Onward.
One thing I can guarantee is that the "fringe" will be on the Cerutti Mastodon like a wet diaper: they've already got a laundry list of "Neanderthal" remains from the New World (some buried in Woodland-age earthen mounds!) and "pre-Flood" sites into which they'll weave this report into. Maybe Bigfoot will even be implicated. Maybe the mastodon was killed by Atlanteans.
Onward.
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