America

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

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

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.

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.

New York Times science writer Amy Harmon has penned an article about the trials of the Genographic Project. The piece focuses on opposition from indigenous rights groups, and the links of the project to the defunct HGDP.

If you sort of know this history already, the article gets interesting on the second and third pages. There is a great description of the troubles faced by Tad Schurr, who is in charge of collecting samples in North America:

But among the 10 geneticists the society has given the task of collecting 10,000 samples each by the spring of 2010, Theodore G. Schurr, the project's North American director, is in last place. Fewer than 100 vials of DNA occupy a small plastic box in his laboratory's large freezer at the University of Pennsylvania, where he is an assistant professor of anthropology. And at the request of the Alaska review board, he has sent back the 50 or so samples that he collected in Alaska to be stored in a specimen bank under its care until he can satisfy their concerns.

The article doesn't do a great job of giving concrete examples of the problems such research might create for indigenous people. Instead, it describes the struggle to combat misinformation -- for example:

Pierre Zalloua, the project director in the Middle East, faces suspicion that he is an emissary of an opposing camp trying to prove their lineages are not important.

Certainly this kind of suspicion is an important aspect of the story -- just as it is for all foreign scientists, although with the added element of DNA sampling, patents, and disease research. Such suspicions are understandable but unfair, and one hopes that the scientists can overcome them.

But the genetic information proferred by Genographic really may cause real problems in some circumstances. The best concrete example is at the end:

In the meantime, his early results have surprised some of the Alaskans who gave him their DNA. In South Naknek, Lorianne Rawson, 42, found out her DNA contradicted what she had always believed. She was not descended from the Aleuts, her test results suggested, but from their one-time enemies, the Yup'ik Eskimos.

The link to the Yup'iks, Ms. Rawson said, only made her more curious. "We want them to do more research," she added, offering Dr. Schurr more relatives to be tested.

I included the last paragraph to make sure to note that this person was pleased and interested in the result. Because, it seems to me that this is exactly the kind of result that is most problematic.

Consider the basis of the result: samples of Aleut mtDNA examined thus far (e.g., this paper by Derbenova et al. 2002, or this one by Zlojutro et al. 2006) generally have one of two haplotypes including one-off variants of these. Published references on Aleut variation have been fairly common, with a total sample size now into the hundreds of sequences. Yup'ik have been less commonly sampled. Rubicz et al. (2003 link) found the following:

The coalescence dates of the Aleut 16212G and D2 clusters also suggest that Aleuts split from related proto-Eskimo groups before or around this same time period [i.e., 3000-4000 years ago]. If correct, then the timing of this fiburcation is generally compatible with dates estimated for the same separation based on linguistic and classical blood group marker data (Harper 1980; Woodbury 1984). In addition, the Aleut 16212G sublineage of haplogroup A is not present in Eskimo populations, and D2 haplotypes are present only in Chukchi and Siberian Eskimos (and one Alaskan Athapaskan), and at low frequencies. Moreover, all Eskimoan groups (Yupik and Inupik) possess the 16265G sublineage of haplogroup A, which is dated at 4398 +- 1574 years, whereas the Aleuts lack these haplotypes altogether. Thus, it appears that Eskimoan populations became genetically distinctive as an ethnic group somewhat later than the Aleuts, but also shortly before the Na-Dene Indians, whose own 16331G sublineage of haplogroup A dates to approximately 3950 +- 2417 years.

That sounds like a way to demonstrate Yup'ik affinities: find the 16265G mutation, and your sequence hasn't yet been found in a sample of 163 Aleuts.

But here is a person whose genealogical history was ostensibly Aleut. The test says she has a haplotype that hasn't yet been found in an Aleut sample. Does that mean that the test has disconfirmed the oral history? Or does it mean that the test has failed to identify ethnographically "true" Aleut? At some level, the question is unanswerable -- if the sample of Aleuts included everyone who reported genealogical affinity with Aleut, then it would include this woman and her haplotype.

So the test is applied to report or "test" an individual's affinity with some group, but it depends on subjective reports from other people to determine the average membership of the group. Which itself entails assumptions about the kinds of genetic movement between groups that has occurred in the past. It is hard to escape a certain circularity.

None of this is a necessary problem for academic interests, which focus on the movements and interactions of the groups. But as applied to group or individual identity, it may create a big problem.

For example, what happens if a person's tribal benefits derive from a relation through a maternal ancestor that the test contradicts? Many people who discover newfound affinities with an unexpected group might not find the academic interest of such a result to be worth the possible cost. And it is very easy to lose sight of the fundamental ambiguity of the test -- it may be suggesting an affinity, for a very small proportion of ancestry, but can it prove it?

The mating and migration interactions of tribes during European expansion were complex, and probably disrupted many longstanding genealogical histories. Considering that complex history, it isn't too far-fetched to imagine a native group with a high proportion of Y chromosome contribution from Europeans, Africans, or some distant tribe. The issue has already emerged as nontraditional people attempt to prove tribal affinities with DNA sequencing. The converse case seems equally plausible -- suppose that a tribe attempting to negotiate a renewal of a gaming compact is confronted with research papers showing that a majority of their Y chromosomes have affinities with Europe. It may not make a legal difference, but might make a large political difference, and most of the high-stakes agreements are subject to the political process.

The other issue that is often raised concerns the value of origins myths. Geneticists view origins myths largely as interesting from an ethnographic perspective but objectively false from an empirical perspective. But in a context -- common to most rural locations -- where children are growing up and leaving their communities in search of educational and job opportunities, cultural legacies including origins myths provide some of the strongest ties opposing dissolution. People who represent the political structure of a group (the "tribal leaders" that emerge in discussions of these genetic issues) have a strong stake in maintaining cohesiveness -- if these elements are lost, then political power is lost as well. And just as the scientists have little investment in indigenous origins myths, most indigenous people have little investment in scientific accounts of their origins. It is good to recognize this fundamental symmetry of motivations: opposing science is often a quite rational strategy.

Most of the people involved in genetic research on indigenous peoples are well aware of these issues, and try to build ties to circumvent them. Indeed, nobody can be successful for long at this work without very sophisticated strategies for communicating the social value of their work.

But certainly a lot of readers are wondering what the problem is -- and may interpret reluctance to cooperate with the agenda of geneticists as mere misinformed intransigence -- akin to creationism. There are certainly similarities between the two cases, but considering the situation as a whole, a lot more interesting dynamic is at work.

Hmm... How will I explain this charge to Gretchen?

You've sent a secure payment of $75.00 USD to American Association of Physical Anthropologists through PayPal. The payment will appear on your card statement as "PAYPAL *AMERICANASS". You'll receive an email receipt shortly.

RPM points to a really clever editorial by Michele Pagano in Cell, titled "American Idol and NIH Grant Review." I'm going to quote the same part, because it captures the rest:

A typical day at one of the many NIH study sections goes something like this. Of approximately 50-70 investigator-initiated/R01 applications reviewed, about half are triaged and the rest are subjected to lengthy discussion, despite the fact that in most of the cases the initial scores are close. Like the amateur singers on the television talent show American Idol, each grant application is evaluated by three reviewers. And, when opinions are conflicting, the three reviewers may display a peculiar resemblance to the American Idol judges, Paula Abdul (sympathetic), Randy Jackson (neutral), and Simon Cowell (hostile). Due to the specialization of science, the discussion is often limited to the three reviewers, with the other study section panelists rarely participating. Indeed, sometimes, while the three reviewers wrangle over a particular application, others are busy on their laptop computers. It is difficult to determine whether these panelists are reading the application under discussion, preparing for the next discussion, or answering their emails. The necessarily inexpert or distracted panelist often sides more easily with the Cowellesque reviewer, who is trashing the application, especially when there is not enough money to go around. This leads to the perception that "the nasty reviewer always wins." Remember, everyone on the study section votes to determine the final score -- even those who are busy with their emails.

Now, see if Simon always won, the show wouldn't be nearly as entertaining. And there is this problem:

Much of the current 25-page format comprises scientific fluff that includes extensive details, alternative strategies/approaches, and pitfalls that are intended to circumvent the critique of whoever is playing the Simon Cowell role.

I just have one suggestion: could they please make it more like Project Runway? I mean, we all know that the successful grants are the ones that are applying to fund results that they have already obtained. That's why they look good -- they have a really good idea what the outcome is going to be.

So if there is already some production, they should get all the PI's to walk their results down a runway to see which ones "work" and which ones don't. Some researchers will be like Robert, running along with whatever trends, but basically predictable and boring. Others will be like Jeffrey -- usually a little "out there", but occasionally really inspired. And after all, aren't most scientific disagreements basically like Jeffrey vs. Laura?

References:

Pagano M. 2006. American Idol and NIH Grant Review. Cell 126:637-638. DOI link

Thanks to an enterprising student, I have an AP story about the discovery of a risk allele for prostate cancer that has different frequencies in different groups.

Scientists have identified a common genetic marker that signals a 60 percent heightened risk of prostate cancer in men who carry it, and it may help explain why black men are unusually prone to the disease, a new study says.

The DNA variant may play a role in about 8 percent of prostate cancers in men of European extraction and 16 percent of the cancers in blacks, researchers said.

So, what does somebody like me do with this information? I'm interested in cases where populations are different as illustrations of human biological variation and its evolutionary causes. Here, we have medical data and genomic information that appears to show a geographic difference among men in their risk. But we have to look at the study to see what that means. Here's the abstract:

With the increasing incidence of prostate cancer, identifying common genetic variants that confer risk of the disease is important. Here we report such a variant on chromosome 8q24, a region initially identified through a study of Icelandic families. Allele -8 of the microsatellite DG8S737 was associated with prostate cancer in three case-control series of European ancestry from Iceland, Sweden and the US. The estimated odds ratio (OR) of the allele is 1.62 (P = 2.7 x 10^-11). About 19% of affected men and 13% of the general population carry at least one copy, yielding a population attributable risk (PAR) of ˜ 8%. The association was also replicated in an African American case-control group with a similar OR, in which 41% of affected individuals and 30% of the population are carriers. This leads to a greater estimated PAR (16%) that may contribute to higher incidence of prostate cancer in African American men than in men of European ancestry.

This is actually a great case study in the complexity of finding the genetic causes of disease:

As only the microsatellite allele showed significant association in the African American case-control group, and it is contained in a smaller LD block in African Americans than in populations of European ancestry (Supplementary Fig. 2 online), we propose that the region most likely to contain the functional variant can be narrowed down to positions 128.414-128.474 Mb (NCBI build 34). This region contains one spliced EST (AW183883) and three single-exon ESTs (BE144297, CV364590 and AF119310) in addition to a few predicted genes, but no known genes. No microRNAs have been detected within the block. Expression analysis in various cDNA libraries confirmed only the expression of the AW183883 EST (Supplementary Methods). We identified four different splice variants of AW183883 by 5'and 3' RACE that were verified by RT-PCR and RNA blot analysis (Fig. 2a). Using the AW183883 EST as a probe on an RNA blot, we detected a 1.5-kb signal only in testis, consistent with the size of the two longer forms. The two shorter transcripts harboring exons 6-8 were detected only in normal (0.6-kb transcript) and malignant (0.6- and 0.9-kb transcripts) prostate cell lines, not in the other tissues analyzed (Fig. 2b,c). The predicted ORFs for these transcripts did not show significant homology to known proteins.

In other words, although they have narrowed down a region around this marker as a risk factor for prostate cancer, they don't know what specific genetic change causes the risk. It isn't any of the SNPs in the HapMap set. They can tell from the HapMap variation that the linkage block is narrower in Africans, so that the causative variant must be fairly near it. There are no characterized genes and no known microRNAs in the region, but there are some possible genes that haven't been characterized. "cDNA" libraries are complements of mRNA expressed within cell lines, only one of these may correspond to the region in question, and one variant is expressed in testis and prostate cell lines. They don't know what it is or what it does.

All of that analysis is bioinformatics -- taking databases of known gene expression in cell lines, genetic variation among people, and identified genes, SNPs and microsatellite markers and integrating them into a picture of associations. What is left is a lot of biology -- what does the key genetic variant change; what gene is it part of; what is the normal role of the gene within prostate (or elsewhere); why does it become pathological; etc. And most important, how can we fix it?

My interest is at the opposite end --- why did this allele become common; why does it have different frequencies in different groups; how old is it?

There are no answers to these questions -- there rarely are in studies like this. But put several of them together and we may start to uncover much about human prehistory and the conditions of life in ancient populuations. Does this risk allele correspond to different ancient environments? Different population dynamics? Or is it just different by chance?

That is the breakdown on the one hand between bioinformatics and biology, and on the other between functional biology and evolutionary biology.

References:

Amundadottir LT and 45 others. 2006. A common variant associated with prostate cancer in European and African populations. Nature Genet (online early) DOI link

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.

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.

Antonio Salas and colleagues have a paper in the October American Journal of Human Genetics concerning the mtDNA affinities of African Americans within today's African populations.

The paper starts with a relatively large set of ~1100 West and Southwest African mtDNA samples, and compares this set with the mtDNA from a similarly large sample of African Americans from the U.S. The goal is to see if it is possible to determine the point of origin for individuals of African descent, at least along the exclusively maternal line.

Normally I don't go in too much for papers like this; although it is valid enough to use mtDNA for these recent comparisons, it is really informative only about a very limited part of an individual's ancestry. The maternal ancestry of many African Americans can be dated to Africa between 200 and 400 years ago; a period of around 10 to 20 generations. Any person has 1024 possible ancestors in the tenth generation in the past (possible ancestors, because later inbreeding may cause some of these people to be the same). Thus, mtDNA is informative about only around a tenth of a percent of someone's ancestry.

The promise of using mtDNA has been that its abundant variation causes strong geographic structure. If people didn't move around too much in their population of origin, the mtDNA type might be specific to a small area, or even a single village. It might tell about only a small proportion of ancestry, but that small proportion might actually be able to be placed with great geographic accuracy.

The current study finds that such accuracy is not possible, at least with the present information. I found the last two concluding paragraphs very informative:

We conclude that mtDNA variation allows us to trace the maternal ancestry of African Americans to broad geographic regions of Africa, with results that are closely concordant with historical studies that now encompass documentation for between two-thirds and three-quarters of the estimated total voyages made during the course of the Atlantic slave trade (Eltis et al. 1998). We have previously raised the possibility of whether, with larger data sets and extensive phylogeographic analyses, more-specific reconstructions will be possible (Salas et al. 2004). However, even with this substantially augmented data set, we note that it is still not possible to go further at this stage. Even with greatly improved geographic coverage, it remains the case that many mtDNAs are very widely distributed throughout the African continent, most likely as a result largely of the Bantu dispersals (Salas et al. 2002), but no doubt also as a result of both earlier and more recent movements, including those that are due to the Atlantic slave trade itself (Salas et al. 2004). This problem will continue to hamper the allocation of African American mtDNAs to narrower geographic locations in Africa, even if the resolution of the molecular analyses is increased from the first hypervariable segment (HVS-I) to complete mtDNA genomes.

Considerable caution is therefore warranted when dealing with claims in the popular media (such as the acclaimed and prestigious BBC television documentary Motherland: A Genetic Journey, first shown in the United Kingdom in 2003) and those made by genetic ancestry-testing companies about their ability to trace the ancestry of certain American (or, for that matter, European) mtDNAs to a particular locale or population within modern-day Africa. Our analyses stand as a warning to unsuspecting members of the public who may be seduced by such promises (Salas et al. 2005:679, citations in original).

A good caution to follow; one that I certainly endorse.

References:

Salas A, Carracedo A, Richards M, Macaulay V. 2005. Charting the ancestry of African Americans. Am J Hum Genet 77:676-680. Full text online

Should we return proboscids, lions and other megafauna to North America's Great Plains? Nature is running this commentary (subscription required) by Josh Donlan and colleagues that argues just that.

Our vision begins immediately, spans the coming century, and is justified on ecological, evolutionary, economic, aesthetic and ethical grounds. The idea is to actively promote the restoration of large wild vertebrates into North America in preference to the 'pests and weeds' (rats and dandelions) that will otherwise come to dominate the landscape. This 'Pleistocene re-wilding' would be achieved through a series of carefully managed ecosystem manipulations using closely related species as proxies for extinct large vertebrates, and would change the underlying premise of conservation biology from managing extinction to actively restoring natural processes.

I can attest to the dandelions, although we have no rats here at the house.

The idea is to start small with species that are already here, such as the Bolson tortoise and wild horses and asses. Then more exotics, like Bactrian camels, Przewalski's horses, and ultimately all the African and Asian animals with extinct American counterparts, including elephants, lions, and cheetahs. They propose starting on large private ranches, and then expanding outward from there:

Large tracts of private land probably hold the best immediate potential for such studies, with the fossil record and research providing guideposts and safeguards. For example, 77,000 large mammals (most of them Asian and African ungulates, but also cheetahs, camels and kangaroos) roam free on Texas ranches, although their significance for conservation remains largely unevaluated.

The third stage in our vision for Pleistocene re-wilding would entail one or more 'ecological history parks', covering vast areas of economically depressed parts of the Great Plains. As is the case today in Africa, perimeter fencing would limit the movements of otherwise freeliving ungulates, elephants and large carnivores, while surrounding towns would benefit economically from management and tourismrelated jobs. A system of similar reserves across several continents offers the best hope for longterm survival of large mammals.

It's a similar idea to the mammoth tundra restoration project I referred to last month. Of course, if they had already gotten Ted Turner on board, I'm sure there would be no need for publicity. As they say, there are already plenty of semi-wild non-native animals on ranches in this country.

I have my doubts about whether the economics will work out in their favor anytime soon, at least across most of the Great Plains. It is certainly true that the population in that area is both aging and decreasing. Hey, I'm a prime example. But the main economic change has been the use of more land by fewer farmers, equipped with better technology, better farming practices, and in many cases greater diversification. There may be some areas of the plains where land values are low enough to make a go of megafauna tourism, but those areas tend to have low carrying capacity for stock.

And it seems pretty implausible to me that ranchers are going to want elephant herds around because they keep the woody plants down (the commentary alludes to this idea). A couple of ranch hands in Montana are not going to sit idly on their horses while a couple of lions attack an elephant on their land.

Then again, it would be entertaining to see the look on a pronghorn's face the first time a cheetah gave it a good chase. As in, "12,000 years of easy living, and now this?!?"

References:

Donlan J et al. 2005. Re-wilding North America. Nature 436:913-914. Full text (subscription required)

Nature is running a short piece (subscription required) on work by Brian Kemp (UC Davis) sequencing DNA from a 10,000-year-old mandible from Prince of Wales Island, Alaska.

The DNA was extracted from teeth, more than 10,000 years old, found in a cave on the northern tip of Prince of Wales Island, off southern Alaska. Researchers compared the pattern of mutations in the DNA against those in thousands of samples. They found matches with 47 Native Americans from tribes living in areas ranging from North America to Tierra del Fuego, showing how the caveman's descendants must have spread.

The story is all over the web, as confirmed by Google and Technorati searches, but few details are available. The best story I've seen yet is at Nature news:

Researchers think they may have found footprints in southern Mexico that mark the oldest evidence for the presence of humans in the Americas.

The impressions, preserved in volcanic ash outside the city of Puebla, have been dated to about 40,000 years ago, beating the oldest accepted evidence of humans in the Americas by some 25,000 years. If proven, the prints would lend support to controversial theories that people reached this land much earlier than previously thought.

The researchers themselves say more work needs to be done to confirm that they have found the mark of human steps. "I believe they are footprints," says geoarchaeologist Silvia Gonzalez of Liverpool John Moores University, UK, who is originally from Mexico. "But we are being cautious, as we need to do more work."

The research is to be published in Quaternary Science Review, but is not available yet. The news stories all agree in noting that the date comes from shell and from direct dating of overlying ash layers. Nature makes a point of skepticism about the footprints themselves, an aspect I've not seen yet in other accounts. The pictures accompanying the stories certainly look like human footprints, but I would expect them to pick the most human-looking ones for the closeup.

I looked for information about the lead researcher, Silvia Gonzalez (John Moores University). She has done a lot of work in geoarchaeology, including some previous work on footprints. Her last project, described by Discovery Channel News focused on the craniometrics of early Americans, and concluded that multiple migrations may have happened. The footprints certainly fit into that pattern.

There really isn't enough information here to make a reasoned opinion possible, so I guess we'll wait and see.

Other stories:

New Scientist
Telegraph (UK)
Technorati search
Google News

Jody Hey (Rutgers) has a paper in the current (vol 3, no 6) PLoS Biology providing estimates of the number of founders of the initial New World human population, along with the approximate date of their arrival (thanks to Dienekes for the link). These estimates were based on analysis of nine genetic loci, including the usual suspects (beta-globin, mtDNA, NRY, Xq13.3, ZFX) and some less familiar ones (ATM, APXL, TNFSF5, RRM2P4).

This paper follows a fundamentally good idea: that evaluation of demographic characteristics of ancient populations must depend upon analysis of multiple unlinked genetic loci. Demography is expected to exert consistent effects on every genetic locus. As long as this is true, adding more loci to an analysis should allow a fuller picture of demographic history. In a nutshell, additional data should allow the statistical testing of more and more parameters relating to population history. So trying to elucidate the founding of the New World by using only a single genetic locus (such as mtDNA) can only test models with one or two parameters.

Such examinations have most commonly attempted to determine the time that New World founding populations arrived. This is done in one of two ways. "Founder analysis" considers the most recent common genetic ancestor for a locus in two populations, and uses the time of that genetic ancestor to infer an upper bound on the time the populations were isolated. Alternatively, examination of frequency spectra of mutations at a locus in New World populations may allow an estimate of the initial time of population expansion, which is generally assumed to correspond to the founding population. These two techniques have been applied most broadly to evidence from the nonrecombining Y chromosome and mtDNA, to varying results.

Hey puts such research into a broader perspective:

For complex historical subjects such as the colonization of the Americas, there are many ways that models can be constructed, examined, and compared. One approach is to develop a portrait based on a particular kind of data, such as linguistic [6], skeletal [14], or archaeological [15] data, or on DNA sequence data from a particular portion of the human genome such as the mitochondria [4,16-19] or the Y chromosome [9]. Yet each source of data has unique sources of variation. In the case of genetic data there occurs a large stochastic variance of the coalescent history among genes that causes different loci to vary widely in levels of genetic variation and in apparent patterns of relationships among populations [20-22]. This stochastic variance is sometimes overlooked, for example in discussions of the histories of the individual DNA sequence haplotypes [18], and it is easy to underestimate the many possible histories that are consistent with a finding that haplotypes are shared by different populations [23-25] (Hey 2005:e193).

The most accentuated point in the article (as reflected by the title) is the finding that the current population of the New World may have been founded by an effective number of fewer than 100 individuals:

In contrast to the Asian population, the New World population parameter (theta₂) is much smaller, and suggests a recent New World effective population size of less than 1,000 (Table 3). However, given the estimate of the effective size of the founding New World population (about 70; Table 4), the overall picture is of a nearly 10-fold growth in the New World effective size since t (ibid).

The conclusion is a simple scenario:

Taken together, the analyses in this study suggest a recent founding of the New World Amerind-speaking peoples by a small population of effective size near 70, followed by population growth in the New World....The analyses reveal very broad distributions for migration parameters, and although the peak locations suggest that gene flow has been fairly high (2Nm values greater than 1; see Table 3), the estimated probabilities of migration rates having been zero are also high (Figure 3G and 3H). Also, because Eskimo-Aleut and Na Dene speakers were not included in this study, the question of separate migrations for these groups has not been addressed [3] (ibid).

But if you think a different scenario for the founding of New World populations is more likely, don't lose heart. There is much in this paper to reveal the limitations of genetic information in testing hypotheses of New World origins.

Hey's discussion notes the limits on his method, including the assumptions that the method makes. It is worth looking critically through the results to see these limitations in action. For example, although archaeological evidence shows that humans arrived in the New World earlier than 12,000 years ago, the maximum likelihood value for this time according to Hey's estimates are only around 6350 years ago. The confidence interval on this date is not given (nor is it obvious from the shape of the likelihood distribution) but would appear to include a range from less than 2000 years ago to over 20,000 years ago.

And these estimates are for one particular assumption of the shape of population size changes in New World populations. If no change is assumed, the maximum likelihood estimate of founding time is earlier than 40,000 years ago. This assumption of constant population size is almost certainly wrong. But the problem is, how can we justify one particular assumption about the style of population growth? In fact, it is precisely this kind of assumption that we would like to derive as a parameter estimate from the data. In this paper, Hey arrives at estimates by assuming that very ancient times of origin could not possibly be correct. This assumption may be validated by archaeological evidence, but that makes it no less arbitrary from a genetic perspective. Indeed, if genetics actually provided a more ancient date as an estimate, there might be good reasons to believe it. For example, there is no conceptual barrier to the hypothesis that the founding New World population actually was isolated from the ancestral Asian population at some relatively early date (e.g., in Beringia), only later to enter the Americas. In such a case, genetics would indicate an ancient population split, while archaeology would show evidence of a recent entry.

What about the estimate of 70 founders? This estimate comes from an estimate of the effective size of the ancestral Asian population (placed at around 9000 individuals) and the proportion of the ancient Asian population that split to found the New World population (placed at less than 0.01). Did one out of a hundred ancient Asians move into Beringia and further to the New World? Quite possibly, who knows? Were there only 9000 people in Asia when the founding happened -- at a time estimated by these genetic data at 6350 years ago? Certainly not.

Consider the ancient Asian population at the time that people first moved into Beringia, perhaps as early as 25,000 years ago or earlier. The evidence about this population applies most strictly to the ancestors of the samples used in the study, which are mostly drawn from China, present-day Siberians, and Korea. Even at the early date of 25,000 years ago, the presence of people in northern Siberia is sufficient to demonstrate much larger populations further to the south, in China. The presence of such larger populations is corroborated by the evidence for widespread colonization out of Southeast Asia into island Melanesia, as well as the colonization of the Japanese islands as far as Okinawa by shortly after 20,000 years ago. We do not know how many Asians there were at this time, but it is almost certainly many times more than 9,000 -- I would guess more than an order of magnitude larger.

We could play games with numbers, assuming that some proportionality between effective and census population numbers existed. Or we could assume that all the parameters but the number of founders were precisely known, and attempt to find the range of variation permissible in that one unknown parameter. But considering all the sources of error, there is no way that any such estimate could have validity. I think the short answer is the most correct in this case: this method tells us essentially nothing about the founding population of the New World.

Would more data from different loci help?

Obviously from a purely statistical perspective more loci means more power, and should allow a greater ability to resolve more population parameters.

But the problems with the current data are not easily addressed by adding more loci or samples. No estimate will have meaning in terms of real population numbers until the relationship between effective size and census size is satisfactorily worked out. In the context of the founding and subsequent growth of a major continental population, this is a major problem. More loci will not answer why these nine give a date much younger than the initial population of the New World could possibly have been founded. This young date must be reflecting a low level of divergence between American and Asian populations for some of the loci used here, but which ones? And why so low? Is there selection on some of these loci?

On the subject of selection, there are clear reasons to think that some of the loci used here may have been under selection in the global population, if not in the New World population. Frequent readers will note that I find selection almost everywhere I look. I tend to be very cautious, because demographic modeling is very sensitive to the assumption of neutrality -- the fact is that natural selection is far more powerful than genetic drift, and can easily throw off the results of an analysis. Hey says this: "Regarding natural selection, the study was limited to loci that had not individually been reported to show evidence of directional or balancing selection," which is a bit misleading, since beta-globin is well known as the primary example of balancing selection in humans, while mtDNA and the NRY violate most tests of neutrality. Although it is unstated, the assumption here is that these loci have not experienced selection within New World populations, which may or may not be true, but is at least problematic. Hey performed an HKA test for selection on eight of the loci, and found a near-significant result (p=0.054). Considering the different loci may exhibit selection in opposite directions (balancing vs. directional), this is not a vote of confidence in the data. The key question is whether evidence of selection globally necessarily affects analysis of New World populations only, or whether there actually has been selection on one or more of these loci in those New World populations. Since some of the model parameters apply to the demography of the ancestral Asian population of origin, I don't think we know the answer to either question.

So I think these issues will need to be answered before genetics will give a clear answer about New World origins.

UPDATE (5/25/05): I wrote the post in a bit of a hurry, and upon reflection I thought a couple of things could be added. My point isn't that genetics hasn't told us anything about New World origins. In fact, I think that founder analysis has added some significant constraints on the date that at least some of the founding populations left Asia. Nor do I think that this is a conflict between archaeology and genetics. The two fields do not currently present alternative hypotheses of origins; instead, they both provide evidence that may test models of the founding population. My feeling is that the archaeology right now provides evidence that is much stronger than anything provided by genetics -- strong enough that it absolutely excludes all but a relatively narrow range of hypotheses.

Consider what archaeology and common sense alone tell us about the founding populations. They must have first arrived earlier than 12,000 years ago, possibly substantially earlier, but certainly not earlier than 50,000 years and probably much more recently. They may have already have been separated for a substantial time from contemporary Siberians, since the geographic extent of Beringia may have put a lot of distance between them. They must have been a relatively small population compared to contemporary Asians. This migration was not the voortrekkers crossing the Vaal; it was a relatively small population of hunter gatherers dispersing into a vast new continental land mass. This means that the population must have begun small and expanded greatly, probably exponentially. There may have been more than one dispersal, with more than one population source.

So given these constraints, what has the genetic analysis in this study added? Does the relatively recent estimate of the date of origin mean that people arrived on the more recent end of the possible range of values? No, because the recent number depends on specific, unverified assumptions, because it lacks any confidence limits, and because it gives an estimate that makes no archaeological sense in any event. Does the estimate of 70 founders add to our knowledge that the founding population was probably small? No, because again there are no confidence limits, and more critically we have no idea what the estimate means in terms of real numbers of people.

In other words, we may know what these numbers are consistent with: they are consistent with some possible hypotheses of origins and additionally a wide range of hypotheses that have been strongly refuted by archaeology. We have no idea what archaeologically plausible hypotheses the numbers are inconsistent with. So they haven't tested anything. Maybe they are the best estimates possible. The demographic model appears sound, the problem is that the data do not allow more precise estimates of the many parameters. Personally, I am skeptical that adding more loci will help very much, since each locus adds the potential of unrecognized problems extraneous to the demography. If this is the future, then genetics are unlikely to provide as much resolution on this problem as archaeology already has.

References:

Hey J. 2005. On the number of New World founders: a population genetic portrait of the peopling of the Americas. PLoS Biol 3:e193.