Sunday, July 10, 2005

Lessons from Kennewick: The Value of One Skeleton

Before going any further I would recommend that you read the first and second posts in this series.

So, having learned some basic things like how to determine gender, ethnicity, age and stature you might think that nothing more can be learned. You might also think that nothing could be learned from a single skeleton. You would be wrong.

The Swan Creek site is located in South Dakota (this example comes from Skeletal Biology in the Great Plains: Migration, Warfare, Health and Subsistence edited by Douglas Owsley and Richard Jantz). It was excavated, mainly, by W. H. Over. The site dates to 1675-1725 and is Coalescent tradition village site (the Coalescent tradition has been attributed to the Arikara and Pawnee). One of the skeletons was somewhat different from the rest. It was found jumbled together with four other skeletons. The skull is labeled 2198 and that is how I will refer to it.
Skull 2198 was judged, using some of the criteria in the last post, to be a male (size, brow ridge, mastoid size, blunt eye orbits, etc) between the 40-50 years old (based on the obliteration of cranial and palatal sutures). Pathology included three healed depression fractures. To determine biological affiliation researchers first used the technique pioneered by Giles and Elliot (mentioned in the second post of this series). This is where the first problem comes in. Giles' and Elliot's method classifies white and black females and white males reasonably accurately. It missclasifies black males and native americans. Giles and Elliot used a sample of native americans from Indian Knoll (in Kentucky) which dated to around 1000 BC. Ever since Franz Boas' classic study on the changes in cranial form between immigrants and their children it has been know that a wide variety of factors effect the shape of the human skull - including environment. So the difference in environment plays a role. It is also known that the accuracy of such techniques drops off when you move outside the population the technique was developed on. Different populations have differing patterns of variability. In this case, Giles and Elliot frequently classifies northern plains indian populations incorrectly. So researchers turned to the method developed by Gill. But, you guessed it, Gill's method gives variable results for northern plains populations also - especially Arikara males. I should mention at this point that both methods classified skull 2198 as a white male. As another means of testing this researchers compared Larson (another collection of Arikara skeletal material to 300 crania from France (dating to 1500-1900 AD) and 100 Austrian crania (1700-1900 AD). They developed their own discriminant fuctions to classify the Swan Creek crania. Thsi new function classifed all Swan Creek correctly as indian - except for two. One of which was 2198 which was classified as European. You might be tempted to say "so what, you found a caucasian skull in an indian village. Big deal!" Well it is a big deal. The earliest documented evidence of European contact with the Arikara wasn't until the 1740's. There is some evidence of French trader activity prior to that time but this is the first tangible evidence. There is also some evidence that the Swan Creek village experienced a reduction in population which is part of an overall disease induced reduction of population that occured in the middle Missouri area. One explanation was that disease was passed along trade routes in advance of the arrival of Europeans. This find suggests disease pathogens were carried in directly by Europeans. This alone makes skull 2198 important. But there is more. If skull 2198 was European this raises the possibility of gene flow. Did he take a native american wife and have children? How can we tell? Presumably, they would be morphometrically intermediate but because of a shared environment would still classify as Arikara. Several of the crania from Swan Creek fell close to being classified as European (technically they were close to the sectioning point - the line that divides European from Arikara). Suggestive evidence that there may have been gene flow - but not conclusive. It would be nice if we could do more research on the issue, unfortunately the W.H. Over Collection (of which Swan Creek was a part) has been repatriated.

This brings us to Brace et al's 1993 article "Clines and Clusters Versus 'Race:' A Test in Ancient Egypt and the Case of a Death on the Nile" published in the AJPA. Ostensibly, this is a study of the biological affinities of ancient Egyptians with other populations around the world. The specific point of the article was to address the notion that Egyptians were "black". Along the way another mystery skull is found.
Let's step back a minute. When discussing ethnicity in my previous post I pointed out that I had been taught to distinguish three basic catagories - Caucasoid, Negroid and Mongoloid. As we saw with the Arikara this is very simplistic. Arikara skeletons vary from other northern plains skeletons which in turn vary with skeletal samples from other geographic areas (not to mention the issue of temporal variation). As I have mentioned a wide variety of things can affect the skeleton. Thigns like healthcare, nutrition, lifestyle (that's an interesting story and the subject of some future post) and evironment. There is one thing that can affect the skeleton that I haven't mentioned yet.
There have been a wide variety of traits used to divide people up into races. Four in particular will be discussed. The four traits in question are usually used to define Negroid or blacks. The first is the amount of melanin in the skin. There are numerous populations around the world with heavy concentrations of melanin in their skin. Such populations can be found in Africa, India, Australia and South America. Given the geographic separation of some of these groups one can say they are not all related (which you would expect if skin color was a diagnostic criteria of biological affinity). Basically the amount of melanin in skin is a response to solar radiation. As such, it is under control of selection and forms a cline or gradient that follows the amount of solar radiation. Another trait used to define the Negroid "race" is the elongation of dital limb segments (those parts of the limb furthest from the body). In point of fact the elongation of distal limbs is related to the dissapation of heat (think Allen's Rule) and is also clinally distributed. Since solar radiation and heat stress are related there is also a correlation between skin color and distal limb elongation. Nasal bridge elevation and elongation is another trait used to define race. Unlike skin pigmentation and limb elongation, nasal bridge elevation is not related to heat, rather it is related to the amount of moisture in the air. Consequently, nasal bridge elevation and elongation is also under selective control and occurs in arid environments (for example in humid areas of west Africa and the Congo nasal bridge elevation is absent. It is present in areas such as the arctic were the air is cold and dry). Jaw and tooth size are also used to define "races". Jaw size is, obviously related to tooth size - hence large teeth tend to create a certain amount of alveolar prognathism (see the previous post). Tooth size, it has been argued, is under selective control related to food processing technology. Consequently, it has a different distribution than traits related to solar radiation, heat or humidity.
So let's see how these four traits play out in Egypt. There is a cline of skin color and distal limb elongation running from the Nile Valley south to the equator. Once we reach the East Horn of Africa (Somalia and the Arabian Peninsula) we face a different situation. Since there is a large amount of solar radiation we see the dark pigmentation and distal limb elongation. It is also very dry so, unlike in other parts of Africa, we also see nasal bridge elongation and elevation. We also see a reduction in tooth size (Brace et al argue that this is because this area was one of the centers for the domestication of plants). Brace et al found that when these traits (i.e. the ones under selective control) were left out Somalis showed a definite relationship with European populations. All this, really, proves Darwin correct when he said traits under selective control can't be used to determine population relationships. Brace et al then examined traits that were not under any kind of selective control. They assumed that:

Traits that show associations with each other only within the context of a given region, then, inevitably have no adaptive significance. When a large number of features occur together in a given geographic area, the principle agent controlling their occurence is the sharing of genes between neighboring groups that are by definition relatives.

They then analyze skelatal samples from all over the world and construct a tree (for the statistically inclined the tree was based on Euclidian distance) of such clusters of populations. Since the traits underlying these clusters are, they argue, nonadaptive they do not easily yield labels such as "black", "white" or "mongoloid". I will get back to this in a bit. One of the skulls included in the analysis was skull E 597 from the 26th-30th Dynasty (dating to 664-341 BC). This skull was utterly unlike anything else in the collection - so much so that Brace almost felt that it had been included by mistake. Except for the fact that there was clear evidence that the brain had been extracted through the nasal aperture. The individual had also been embalmed with the mortuary treatment reserved for wealthy Egyptians. Discrimant function analysis of skull E 597 was more closely related to a sample of skulls from the neolithic in Germany! Leaving aside the question of how this individual came to be in Egypt, skull E 597 indicates some interesting things about Egypt. Brace et al's analysis indicated that Egyptians in Late Dynastic times shared more traits in common with Europeans than with the inhabitants of Upper Egypt 3,000 years earlier. Which indicates the extent of contact Egypt had with populations to the north and west in particular and the rest of their known world in general. In a sense, the significance of skull E597 is that simple labels such as "Caucasoid" or "Negroid" are misleading and inaccurate.
As Brace et al point out:

Where human traits have adaptive significance, their distributions are determined by the distribution of the controlling selective forces and 'their are no races, their are only clines." Where traits have no adaptivie significance, neighbors will share traits with neighbors and analysis of adjacent samples will show that they cluster together. Both these situations occur in the Nile Valley....
The old-fashioned chimerical concept of "race" is hopelessly inadequate to deal with the human biological reality of Egypt...

So there we have it. New methods for learning about history were tested. Questions that we had never tried to ask before (anthropologically speaking)were raised. One skull taught us something new about American history. One skull taught us something new about Egyptian history. Both taught us something about ourselves by leading us to questions certain notions about race - which means we might be able to have a more meaningful conversation. The value of one skelton in each case made a difference in the advancement of human knowledge.

I hope to have the next (and final post) in this series up by Tuesday.