Mexican footprint media
The BBC reports on a BBC program covering Silvia Gonzalez and the Cerro Toluquilla "footprints". (I have a roundup of stories from the initial announcement. )
The new BBC article gives a good account of how they were found and the context they are in. The big problem is the dating:
More controversial still are the dates. Colleagues of Silvia Gonzalez at Oxford University used a technique called optically stimulated luminescence (OSL) that records the last time rocks were exposed to sunlight or heat.
That gave a variety of dates from the overlying sediments, but when applied to small fragments of what looked like brick or burnt clay within the volcanic ash, it produced a date of about 40,000 years.
That initially shocked Dr Gonzalez as it implied by far the earliest evidence of humans in the Americas. But it fitted in with dates of up to 38,000 years based on carbon 14 in shells in the sediments above.
The dispute right now boils down to a "last gasp" by Gonzalez. Paul Renne's group found that the ash layer dates to 1.3 million years by Ar-Ar. But there is always a chance that the layer was actually redeposited by water from an earlier ashfall. At 1.3 million years old, the ash layer ought to have reversed polarity, since the last period of normal polarity began 780,000 years ago. When Renne's team checked the polarity of the ash, they found it does have reversed polarity. So the evidence is very strong that the ash layer is 1.3 million years old.
Here's Gonzalez' argument:
Silvia Gonzalez' view? "We know that there are short-term 'excursions' of the magnetic field, and one of those happened 40,000 years ago, very interestingly."
Why is this special pleading? Because the ash is still 1.3 million years old! So for the "footprints" to be 40,000 years old, the ash must have been redeposited from some earlier source, and been plastic at just the time of a paleomagnetic excursion.
I love Renne's reaction:
Professor Renne: "How did I know they were going to say that? There is a finite possibility that that is correct, but the probability is extremely low."
That's why I try not to disagree with geochronologists!
It would be one thing if there were clearly consistent footprint trails. But there aren't. Since it's the floor of a quarry, I expect eventually to hear someone come forward who knows how the marks were made.
Chaw joins poop in archaeology arsenal
Well, archaeology is set to receive a once-in-a-generation influx of interest from teenagers drawn to the allure of the past. I mean, from the new Indiana Jones movie, of course.
So what do they have to go and do? Discover a real life crystal skull? Sorry, kids. If you want to be an archaeologist, it's all bodily functions from here on out.
Tom Dillehay and colleagues (2008) report in this week's Science that they have found chewed-on seaweed "cud" from Monte Verde, dated to 14,000 calendar years BP. And that paper is right next to the final publication of the Paisley Caves coprolites from Oregon, also dating to slightly before 14,000 calendar years BP.
Both papers are pretty cool -- together they emphasize that these kinds of forensic evidence are becoming increasingly important in documenting the activities (and existence) of archaeological populations. After all, a person has to poop thousands of times during his life, but he has only one skeleton.
Dillehay and colleagues interpret their seaweeds as a specialized medicinal collection, based on the presence of non-edible species and species present at different times of the year. Here's a quote from Michael Balter's news piece on the find:
Back 14,000 years ago, Monte Verde was located about 90 kilometers east of the sandy Pacific coast and 15 kilometers north of a rocky-shored inland marine bay. Algae from both environments were recovered, including inedible species that are today used as medicines in Chile and elsewhere. Moreover, the algal species found are known to flourish at different times of the year, suggesting to Dillehay's team that the Monte Verdeans were intimately familiar with coastal resources--possibly because they had originally arrived in the region via that route. Erlandson agrees: "The variety of seaweeds implies a pretty deep knowledge of coastal ecosystems and a long history of exploiting them."
Well, that's pretty impressive, even if the seaweed were chewed up. And hey, my kids are much more interested in bodily functions than they are in crystal skulls. So maybe this will bring in new archaeologists after all!
References:
Balter M. 2008. Ancient algae suggest sea route for first Americans. Science 320:729. doi:10.1126/science.320.5877.729
Dillehay TD, Ramírez C, Pino M, Collins MB, Rossen J, Pino-Navarro JD. 2008. Monte Verde: Seaweed, food, medicine, and the peopling of South America. Science 320:784-786. doi:10.1126/science.1156533
Gilbert MTP and 12 others. DNA from pre-Clovis human coprolites in Oregon, North America. Science 320:786-789. doi:10.1126/science.1154116
New news in New World settlement
Afarensis has a post on Brazilian evidence relating to the origins of Native Americans (via Gene Expression). It's a good summary of recent work by Neves and colleagues, including the background to this:
In essence, Neves et al, is saying that Paleoindians were part of the expansion of H. sapiens out of Africa, whereas Native Americans represent a later expansion of specialized populations. I find this suggestion intriguing. There are skeptics, as you can see from the above quote from The National Geographic article. Powell is arguing that because America was populated by small populations, genetic drift would kick in and you would see a lot of variation between populations and that the Lagoa Santo populations fit within the pattern af variation seen in Native American populations. If that is the case, I would expect one or two populations to display morphology similar to Australians and Melanesians. Instead, what we have is a series running from southern Chile to Florida - and now Kennewick in Washington (which was not included in either study)- all of which display morphology similar to Australians, Melanesians and Polynesians.
The idea of a "generalized" form for early modern humans has been around for awhile now, applied not only to Paleoindians, but also the Upper Cave crania from Zhoukoudian, and -- by some -- early modern Europeans.
Taking the "re" out of repatriation
Writer Rachel D'Oro of the Associated Press reports on the repatriation of human remains from On Your Knees Cave, Prince of Wales Island, Alaska:
ANCHORAGE, Alaska - Human remains estimated to be more than 10,000 years old will be returned to southeast Alaska Tlingit tribes 11 years after they were found in a cave in the Tongass National Forest.
It's the first time a federal agency has conveyed custody of such ancient remains to indigenous groups under the Native American Graves Protection and Repatriation Act, U.S. Forest Service officials said Friday.
...
Vertebrae, ribs, teeth, a mandible and a pelvic bone were among the remains discovered in 1996 during a Forest Service archaeological survey for a proposed timber sale on northern Prince of Wales Island. The area is the aboriginal homeland for Tlingit tribes.
Prince of Wales Island is in the Alaska Panhandle, near the British Columbia border.
Some archaeologists, noting the island's placement on the coastal fringe of Beringia, have suggested that it may document some descendants of the earliest settlers of lower North and South America. In this model, people were able to bypass the Cordilleran ice sheet by skirting southward along the coast of the Pacific Northwest. The first Americans lived significantly earlier than this site, which dates at the earliest to around 10,300 radiocarbon years. But the location makes the remains possibly the best skeletal representation of the original inhabitants of the Americas.
Rex Dalton described the site briefly in a Nature news article from 2003:
In the north of Prince of Wales Island, he ventured into the 'On Your Knees' Cave -- so named because it can only be entered by crawling through a narrow tunnel -- which turned out to contain a host of specimens. Subsequent years of summer digs by Heaton and his archaeologist colleagues have unearthed the oldest signs of human habitation in the Pacific Coast region, from sediments in the cave's floor.
The specimens include a bone tool that has been radiocarbon dated to 10,300 years ago, a human bone dated at 9,200 years old, and blades made from obsidian -- a volcanic glass found in lava beds -- of the same vintage. The latter have shown the ancient inhabitants of Prince William Island to be relatively well-travelled coastal seafarers. Craig Lee, an anthropology doctoral student now at INSTAAR, has used X-ray fluorescence spectroscopy to examine trace elements in the obsidian, and so determine its source. His studies show that the material in On Your Knees Cave came from Suemez Island, about 150 km to the south, and Mount Edziza, nearly 400 km to the northwest in mainland British Columbia.
Long-distance contacts along the coast, and between coastal and inland locations, among the early descendants of the New World invaders show the potential for rapid movement down the western coast of the Americas.
That archaeology expresses how important the site is for understanding early New World populations. But what about the skeleton -- how have the human remains contributed to our knowledge?
These remains are relatively fragmentary and therefore don't provide a lot of anatomical information that could be compared to recent people. But they contain a wealth of genetic information, of the kind that has been retrieved more and more routinely during the last 10 years.
Kemp and colleagues (2007) examined the DNA from the human remains, successfully extracting both mtDNA and Y chromosome markers that permitted analysis of the specimen's place relative to New World diversity. The conclusions help to emphasize the importance of such early skeletal remains:
Mitochondrial and Y-chromosome DNA were analyzed from 10,300-year-old human remains excavated from On Your Knees Cave on Prince of Wales Island, Alaska (Site 49-PET-408). This individual's mitochondrial DNA (mtDNA) represents the founder haplotype of an additional subhaplogroup of haplogroup D that was brought to the Americas, demonstrating that widely held assumptions about the genetic composition of the earliest Americans are incorrect. The amount of diversity that has accumulated in the subhaplogroup over the past 10,300 years suggests that previous calibrations of the mtDNA clock may have underestimated the rate of molecular evolution. If substantiated, the dates of events based on these previous estimates are too old, which may explain the discordance between inferences based on genetic and archaeological evidence regarding the timing of the settlement of the Americas. In addition, this individual's Y-chromosome belongs to haplogroup Q-M3*, placing a minimum date of 10,300 years ago for the emergence of this haplogroup.
Possibly the most significant aspect of ancient specimens is their ability to inform directly about the rate of sequence changes over time. Phylogenetic rates of change in mtDNA (e.g., between humans and chimpanzees) appear to have been relatively slow compared to the observed number of mutations between parents and offspring. There are two reasons for this: Some mutations are lost because of purifying selection, and some recur again and again at the same site, and therefore saturate over long time scales. But it is difficult to estimate the relative importance of these factors, and therefore it is hard to assign rates across different time scales (e.g., the founding of New World populations, modern human origins, etc.). Kemp et al. (2007) used the ancient mtDNA sequence from On Your Knees Cave to arrive at an estimate of the rate of change across the 10,000-year span, which ought to allow a more precise chronology for the New World founding:
Applying our most conservative rate of 34%/site per myr (95% CI 15-53%/site per myr) to the nucleotide diversity estimate (pi = 0.86) for mtDNA haplogroups A, B, C, and D in Native Americas (Bonatto and Salzano, 1997b), indicates that human entered the Americas ca. 13,438 YBP (95% CI 8,113-28,667
YBP). While this estimate does not preclude the possibility of an early entry, the estimate is also compatible with an entry more recent than 15,000 YBP (Kemp et al. 2007:617).
That is in contrast to some earlier genetic estimates, which had suggested founding times as early as 40,000 years ago -- often suggested as compatible with a very long-term occupation of Beringia.
Soon, we will surely see more testing of early specimens to try to assess the genotypes for other loci. For example, the idea of an early population bottleneck during the founding of New World populations has become an important hypothesis for explaining the limited variation of many genes in the Americas. But later events may also have been important in limiting variation. For example, Native American populations have substantially less allelic variation at HLA loci than do Asian populations. This reduction in diversity probably began with the initial founding and subsequent dispersal, but may also have involved natural selection during the last 10,000 years. The importance of the initial bottleneck may be tested by finding HLA types for early American skeletons -- if the founding event was almost solely responsible for the current HLA diversity, then the early skeletal samples should be comparable in diversity to recent samples. If they show much more diversity (for example, HLA haplotypes absent in recent Americans) then we can conclude that selection in later populations played more of a role -- implying a different scenario for pathogen-host evolution over time in the Americas.
In that light, repatriating a 10,000-year-old skeleton must subtract from our future inquiries into the origins of New World peoples. Or I should say, patriating, since it isn't being sent back to its people, it is being given to entirely new people who have no demonstrated relationship to the skeleton at all.
I do perceive the real benefits from cordial and cooperative relationships with indigenous peoples, particularly where tribes have well-defined and recognized historic territories. The vast majority of skeletal remains of ancient Americans are quite recent, and might in most cases (given sufficient evidence and analysis) be attributable to particular historic cultural groups.
But for remains over a few thousand years old -- and certainly for the earliest New World populations -- every living person of Native American descent may count these early skeletons among their ancestors.
References:
Dalton R. 2003. Archaeology: The coast road. Nature 422:10-12. doi:10.1038/422010a
Kemp BM and 13 others. 2007. Genetic analysis of early holocene skeletal remains from Alaska and its implications for the settlement of the Americas. Am J Phys Anthropol 132:605-621. doi:10.1002/ajpa.20543
Pig extinctions in Polynesia
I happened across an interesting article from last year by Christina Giovas that looks at pigs in Polynesia. People carried pigs with them to most of the islands that they colonized, excepting some distant and relatively recent places such as Rapa Nui (Easter Island) and New Zealand. These places presumably didn't get pigs, either because sufficient numbers did not survive the initial ocean voyage, because of low rates of subsequent contacts that might have brought pigs, or because the necessary forage for pigs was not present in sufficient quantity to establish them -- especially since pigs and people compete for many of the same foods.
But some islands that didn't have pigs at the time of European contact nevertheless have ancient archaeological evidence of pigs. So people brought pigs to those islands and established them, but they subsequently died out.
Here are the key paragraphs form Giovas' introduction:
Nonetheless, archaeological data in combination with the accounts of early European explorers reveal a pattern of pig distribution far more extensive in prehistory than at the time of historic contact (Fig. 1) (Alien et al. 2001; BayPetersen 1983; Bellwood 1987; Dye and Steadman 1990; Kirch 1991, 200Ob; Kirch and Yen 1982; Rolett 1998), suggesting that prehistoric Polynesians either allowed swine herds to die out or intentionally exterminated them. Whichever of these is the case, it appears that pig extirpation in Polynesia constitutes one of the few known instances of domestic species extinction (Ramis and Bover 2001), making it highly significant to the history of human-domesticate interactions.
It has been suggested that animal husbandry was simply less feasible on resource-impoverished islands (Anderson 2001, 2002; Bay-Petersen 1983; Kirch 2000b), particularly since husbandry practices involved feeding pigs cultivated crops, setting up an element of resource competition between pigs and their Polynesian keepers. Underlying this explanation are assumptions about island ecology and its impact on pigs and humans alike. Although the relationship is seldom made explicit, these ecological factors are presumed to operate according to principles of island biogeography, particularly the relationship of island area to species extinction. Other factors may also influence the likelihood of extinction, including island geology, elevation, and latitude and longitude. Here I test the relationship between pig extirpation and these variables. I propose that the pattern of prehistoric distribution for domestic pigs in Polynesia may be best understood in island biogeographic terms and that resource competition may represent the overarching causal mechanism driving pig extirpation, as Kirch (2000b) has argued. To begin, I offer a brief overview of the role of pigs in Polynesian society, followed by a discussion of the relevant principles of island biogeographic theory and the mechanisms-both environmental and cultural-that may have brought about pig extirpation in Polynesia (Giovas 2006:69-70).
Obviously, on the islands where pigs were extirpated, humans were a factor in killing them. But there is this question: did extirpation sometimes result from a deliberate plan, where people recognized that the pigs were eating vegetable foods the people needed themselves? Or did they just eat all the pigs, possibly during a shortfall, and not restock them from other islands.
In times of resource shortfall, pigs would have been effectively competing with people for the same agricultural produce, placing Polynesians in a position in which the benefits of pig husbandry may have been outweighed by its relatively high economic (energetic) cost. As Kirch and others have suggested (Alien et al. 2001; Bay-Petersen 1983; Kirch 2000b), trophic competition on this level may explain why animal husbandry failed in many parts of Polynesia. Those islands prone to resource shortfalls would have been at a greater risk for failure of pig husbandry simply because crop harvests may have been insufficient to support both humans and pigs. The onset of this effect need not have been sudden or severe. Instead, it may have operated slowly but systematically over decades or more (Giovas 2006:72).
Since many of the islands were in periodic contact with other societies, pigs might have redispersed in a number of cases, and possibly pigs were maintained over long times on some islands that otherwise would have lost them by recurrent contact. Giovas approached this issue of "social isolation" in an interesting way:
On the other hand, where human interaction between islands was frequent, it may have supplied a type of rescue effect (Brown and Kodric-Brown 1977) in which the continual immigration of domesticates safeguarded against their disappearance from an island. In this scenario, isolation comprises not only a geographic but also a social component in which substantial geographic isolation may be overcome in part by cultural forces. Weisler (1994, 1995, 1996, 1997; Woodhead and Weisler 1997), for example, has documented the existence of a long-distance economic interaction sphere among the remote islands of Mangareva and the Pitcairn group. The subsequent decline of settlements on Pitcairn and Henderson may have come about in part because of the breakdown of interisland voyaging between these islands (Giovas 2006:75, emphasis in original).
This concept of social isolation serving as a substitute for geographic isolation is very interesting to me; it adds a historically fluctuating component to the usual isolation factor treated by biogeographers.
Giovas found that island area was a strong predictor of whether pigs were extirpated, with most of the cases of pig loss being relatively small islands. That is in line with the prediction of island biogeography, at least in terms of the ability of larger islands to support more species within a given ecological space.
Island elevation was also related; extirpation was more likely on very level atolls. But it wasn't clear that this correlation remained true after controlling for island area; the two have a strong relationship. Still, a higher island might be one where humans have more trouble using all resources, as some remain at altitudes or on slopes used only occasionally by people. In other words, a higher island has more potential "wilderness" space where feral pigs might escape and avoid capture.
I find myself wondering whether an additional historical component may be important. Pig populations have the potential of growing quite a bit faster htan human populations, especially when human consumption of them is relatively low and natural forage is available. In other words, during the early years after a colonization, pigs may have grown faster than people.
But later in time, the people caught up in many islands; putting more and more pressure on the ecological space available to both people and pigs. In these contexts, the pigs would have lost out. So demographic growth and competition between humans and pigs predicts a pattern in which many islands start with pigs, but then lose them as human populations catch up and overtake them in size.
We might predict on this demographic basis that pigs would have died out on other, larger islands if Polynesian history had continued without interruption from European explorers. No island was likely to have been a steady-state with equilibrium in pig and human population sizes, although the joining of nearby islands into interacting culture groups might have moderated the effect.
References:
Giovas CM. 2006. No pig atoll: island biogeography and the extirpation of a Polynesian domesticate. Asian Perspectives 45:69-95.
Nobody but us chickens
Chickens were brought to South America in Precolumbian times by Polynesians.
It's all over the wires, so I'll just point to John Noble Wilford:
That is the conclusion of an international research team, which reported yesterday that it had found "the first unequivocal evidence for a pre-European introduction of chickens to South America," or presumably anywhere in the New World.
The researchers said that bones buried on the South American coast were from chickens that lived between 1304 and 1424. Pottery at the site was from a similar or earlier time. A DNA analysis linked the bones, which were excavated at El Arenal on the Arauco Peninsula in south central Chile, to chickens from Polynesian islands.
About half the news articles seem to be leading with, "Why did the chicken cross the Pacific Ocean?" This one is no exception. Har, har, groan.
I don't really have much to say about it, it seems like a very straightforward discovery. There is a radiocarbon date and the DNA evidence. Also, the early postcontact historical record corroborates:
Others thought [chicken arrival with the Spanish] unlikely, noting that when the Spanish invaded Peru in 1532, they saw chickens being used in traditional ceremonies. It seemed hard to believe, some scholars pointed out, that chickens would have been so rapidly dispersed from the east coast to the west and already be incorporated in religious events.
Charles Mann's book 1491 doesn't review this example, but it does talk about analogous kinds of early post-contact documentary evidence from New World peoples. It seems to be an increasingly important source of information to corroborate archaeological findings.
And the chicken transfer does help to explain the sweet potato problem:
The presence of the South American sweet potato in pre-European sites in Polynesia indicated some prehistoric contact between America and the islands.
I've never understood why this has been so quickly waved away. I mean, just last month this Nature News article reviewed a study that claimed that sweet potato seeds could have traveled to Polynesia on a free-floating unmanned ship.
Good grief. I suppose the chickens manned the boat. Er, chickened the boat?
Foods like these have to be among the fastest things to diffuse, even given relatively rare population contacts -- and certainly the Postcolumbian exchange between New and Old Worlds demonstrates this. I suppose the most negative evidence is the lack of evidence for other South American crops, like maize. Maybe the sea travelers used it all to feed the rats?
I mean, rats made it as far as Easter Island, why not the next step? Maybe some South American rats are actually Precolumbian also?
The only thing faster is disease -- and fortunately for the Americas, eastern Polynesia didn't have many of those to transfer.
Wilford's article ends with this:
Scholars found it disappointing and puzzling that the Polynesians who landed at El Arenal left nothing more than chicken bones. Pottery at the site is in a local style. Perhaps the visitors ate and ran, but not without leaving behind some starter chickens for future plates of arroz con pollo.
This seems quite obvious: the chickens were introduced a lot earlier than 1304. They would perhaps have been the longest-lasting element of the cultural transfer -- they wouldn't even have necessarily required permanent settlements, although a more substantial presence might well have occurred. Chickens are the most sensitive sign we can expect to see, just as sweet potatoes are the most sensitive sign on the other side of the contact. You aren't going to find the one place where Polynesians showed up -- you are going to find some site 500 years later when the chickens have spread across half the continent.
John Hawks Department of Anthropology
University of Wisconsin—Madison
Copyright © 2007 John Hawks