I’ve been waiting for this paper for months! The Willerslev group has just published the results of their study on ancient DNA from Paleo-Eskimos in the North American Arctic. Unfortunately, this article is behind a paywall at the journal Science, but I’ll give you a brief summary of the results, and talk a bit about why this paper matters and what it means for our understanding of the peopling of the Americas. Continue reading
Nicholas Wade has a problem. Although his new book, “A Troublesome Inheritance: Genes, Race and Human History”, appears to be selling well, he’s not encountering the praise that he expected from biologists for “courageously” freeing them from the “intimidating social scientists” on the subject of race).
What is he arguing? I go over this briefly in my recent piece on the Huffington Post, and in much greater detail here on this blog, but essentially Wade is using patterns of human variation in populations as a justification for claiming that race is a valid, biological taxonomic category. He goes on to speculate (and that’s really the only word for it, since his claims are unsupported by the preponderance of scientific evidence) that these racial differences determine behavioral differences and thereby explain why some civilizations have historically been more successful economically and politically than others. (You can guess which races he’s talking about; his speculation happens to coincide neatly with traditional stereotypes.)
Wade claims that all critics of this viewpoint are motivated by political concerns and ignore data showing that races are genetically distinct enough to be meaningful taxonomic categories of humans. His book relies particularly upon one genomics study to support this point. In his words (emphasis mine):
Raff and Marks take issue with one of these surveys, Rosenberg et al. 2002, which used a computer program to analyze the clusters of genetic variation. The program doesn’t know how many clusters there should be; it just groups its data into whatever target number of clusters it is given. When the assigned number of clusters is either greater or less than five, the results made no genetic or geographical sense. But when asked for five clusters, the program showed that everyone was assigned to their continent of origin. Raff and Marks seem to think that the preference for this result was wholly arbitrary and that any other number of clusters could have been favored just as logically. But the grouping of human genetic variation into five continent-based clusters is the most reasonable and is consistent with previous findings. As the senior author told me at the time, the Rosenberg study essentially confirmed the popular notion of race.
It’s not a question of logic, but rather what the data show. Rosenberg et al. (2002)’s paper did not analyze or identify just 5 clusters, but rather it considered 1-20 clusters. What Wade is omitting from his paragraph above (and also from his book) is that Rosenberg and colleagues never presented any statistical justification for the choice of 5 clusters over any other number.
Here are the specifics of my criticism, which I posted in response to a commenter on my blog. (If you’re not interested in the statistical refutation of Wade’s argument, feel free to skip this paragraph. I hope Wade takes the time to read it, though). Continue reading
More than 12,000 years ago, a young teenage girl walking through a deep cave (known today as Hoyo Negro) fell down a massive pit. The fall fractured her pelvis, and she died among the remains of giant ground sloths and saber-toothed cats who had met a similar fate. Over the next few millennia, the pit filled with water and their bones were covered with cave formations. They were left undisturbed until discovered in 2007 by cave divers, who named the girl “Naia” in a reference to Greek mythology.
Today, a team of archaeologists and geneticists announced the results from sequencing her mitochondrial genome. She possessed a haplogroup (D1) that evolved in Beringia and is seen in modern Native Americans.
So why is this result so important? The Hoyo Negro girl, like other Paleoindians (the oldest inhabitants of the Americas), had a skull shape that was distinctive from later (younger than 9,000 years before present) ancient Americans, who more closely resembled modern Native Americans. Continue reading
This is the second post in a series discussing the recent publication of a 12,500 year old genome from Montana. You can find the first post here.
In the weeks following the publication of the complete genome from a Clovis child, there’s been a lot of press coverage of this study and its possible implications. I want to discuss a bit of the media coverage on this subject, since it raises issues that I think science journalists need to consider more carefully.
First of all, to recap the major findings of the original study (discussed in more detail at the link above):
1. Anzick-1, the 12,500 year old Clovis child whose genome Rasmussen and colleagues sequenced, is very closely related to living and ancient Native Americans.
2. Anzick-1 is more closely related to Siberians than other Eurasian groups.
3. Anzick-1 is more closely related to Central and South American Native American groups than to some North American groups.
4. The results from Anzick-1’s genome fit with the scientific consensus about the peopling of the Americas. This consensus encompasses the results of decades of archaeological, genetic, and paleoclimate research.
Unfortunately, several press reports chose to find controversy in a decidedly non-controversial story by giving undue weight to problematic “alternative” explanations of Native American origins, including the Solutrean hypothesis, and other “European contributions” to Native American ancestry.
Last Wednesday, Dr. Morton Rasmussen of the Natural History Museum of Denmark and his colleagues announced that they had completely sequenced the genome of an infant boy, buried ~12,600 years ago in Montana. A few weeks earlier, I’d been approached by an editor at Nature, who asked me if I and my mentor Deborah Bolnick would be interested in writing a companion paper that would analyze and contextualize their results. We agreed, and the paper was published in last week’s issue, alongside Rasmussen et al.’s work. Because it’s (unfortunately) behind a paywall, I’d like to summarize what we said in that paper for non-scientists. There are a lot of things to talk about with regard to this study, including a consideration of ethical issues and the media’s response, so I’m likely going to do several posts on it. This first post is mainly a discussion of how we interpret the results.
I haven’t been writing as much here recently, because I’ve been working on a “News and Views” article for Nature….and now I can finally talk about it! Here’s a link to my article: http://www.nature.com/nature/journal/v506/n7487/full/506162a.html, and to the paper that it’s discussing: http://www.nature.com/nature/journal/v506/n7487/full/nature13025.html. In the next few days I’ll post something here to discuss the main points of the article (for those of you who can’t access it), and also my reaction to the media coverage that the study is getting.
It seems that every week there are exciting new findings from ancient DNA research. This is wonderful news, because we’re learning incredible things about the relationship between humans and Neandertals, the prehistory of ancient populations, and even previously unknown hominins. But on the flip side, we’re also seeing news reports of extremely questionable results, and I’ve gotten more than one inquiry recently from people excited or confused by them. I though it would be a good idea to write a bit about how regular people can figure out whether a study is legitimate or not.
The first step in distinguishing good ancient DNA studies from bad ones is the same as distinguishing pseudoscience from legitimate science in general: ask where the results are published. Are they in a peer-reviewed journal? Or does the author present it as “science by press release,” stating something like:
The next steps require you to know a bit about ancient DNA itself, and how research is conducted. What most casual readers may not understand is how difficult recovering DNA from ancient remains is….and how easily it can become contaminated.
The TL;DR version is that for an ancient DNA study to be considered authentic, at minimum it:
- Must be conducted in the proper facilities
- Must be conducted by personnel practicing sterile techniques
- Must utilize negative controls
- Must have a subset of results reproduced by an outside laboratory
- Must yield phylogenetically reasonable results (or produce extraordinary evidence to support unusual results), that match the characteristics of ancient DNA.
- Must conform to any additional standards necessary, depending on the sample and experimental design