As I wrote in a recent post an article was recently published in the British Dental Journal comparing skulls from people who died from the black plague in 1348 (13 males and 17 females) to skulls of people who died in the wreck of the Mary Rose in 1545 (53 males, 1 female) and with skulls of modern individuals (16 males, 15 females, actually, the measurements were taken off radiograms). Eleven standard cranial measurements were taken and converted into angular and linear measurments. Below is a picture illustrating the angular and linear measurements.
An ANOVA was then performed grouping by era. Results indicated that there were some statistically significant differences between the modern goup and the earlier samples – particularly in the area of cranial vault height and maxillary area. In particular, vault height measurements have increased and the maxillary measurements have decreased. So what does it mean?
Let’s say we are walking along, hiking in the woods, and we find a skull. First thing we would do is report it to the police. But this is a hypothetical example and so we can take the skull back to our lab and start to analyze it. There our a number of things we can learn from the skeleton and the skull in particular. With this skull though, we are only going to be concerned about learning the age. In particular, we are going to look at suture closure. During the mid-1920′s T. Wingate Todd wrote a series of papers, published in the American Journal of Physical Anthropology, concerning endo- and ecto-cranial suture closure. He based these studies on the Hamann-Todd collection. During growth provision needs to be made, obviously, for continued growth of the brain. Sutures are that method (to be very simplistic). After growth stops the sutures begin to knit together and disappear. If we get a lrge sample of crania spread across a wide variety of ages, ethnicities and both sexes, we can create a staging method that will allow us to determine the approximate age of the skull. The picture below illustrates the general idea.
Over the years the Hamann-Todd and another collection, the Terry Collection were used to create a number of techniques to determine age, sex, ethnicity and stature, among others. Over the years anthropolgists such as Mildred Trotter (a fascinating woman, this is one link you should follow), T. Dale Stewart. Wilton Krogman and WIlliam Bass, used these techniques (and created others) to create the field of Forensic Anthropology. By the 1980′s, forensic anthropologists were noting some discrepancies between, say the age estimated by cranial sutures and the true age obtained after a positive ID was made. One, naturally, would like to know what is causing these changes. A 1988 paper by Jantz and Moore-Jansen (A Database for Forensic Anthropology: Structure, Content and Analysis, UT Dept. of Anthropology Report of Investigations #47) examined the question and determined that three issues were playing a role in the discrepencies.
First, the Hamann-Todd and Terry collections were composed of whites and African-Americans only, whearas this is not true of the population of the US (why this is the case is too complicated to go into here).
Second, the people composing these samples were, for the most part, born before 1900 (in some cases as early as the 1860′s). During the intervening period there have been changes in nutrition, access to healthcare, reduction of infectious diseases and sanitation. To understand how this affects our ability to, say determine age, let’s look at healthcare. Because of better healthcare, most – but not all – US populations are living longer. Returning to our example of cranial suture fusion, what this means is that the sutures continue to be obliterated. But when we use standards based on Hamann-Todd a funny thing happens. The ages of older individuals (not included in Hamann-Todd) are underestimated, whereas the age of some younger individuals is overestimated. As another example we can look at nutrition. There are an number of studies that indicate that malnutrition affects growth rate (more so in in males than females) and this would, ultimately, be reflected in skeletal morphology.
Third, demographic characteristics which I will pass over in silence.
In the meantime, anthropologists were studying the effects of changing lifestyles and environments on human skeletal morphology (Brace’s Environment, Tooth Form, and Size in the Pleistocene, published in Man in Evolutionary Perspective is a good example). Carlson and Van Gerven’s 1977 paper in the AJPA is another good example – and gets us back to the point of this post. Carlson and Van Gerven studied the craniofacial morphology of a sample from Nubia ranging from 12,000 bp to 1500 AD. What they found was that the latter Nubian sample had, you guessed it, increased cranial vault height and reduced maxillary area compared to the earlier Nubian samples. They attribute the differences to a change in subsistence from foraging to food production (and the resulting shift to consumption of softer foods).
In the British Dental Journal paper, researchers found statistically significant differences between their samples in these areas. Most of the differences occured between the 1545 sample and the modern sample, with only minor differences between the 1348 and 1545 samples (without knowing a lot more about English history I would be hesitant to speculate as to what changes led to this). What this goes to show is that the results of the interaction between genotype and environment can be quite interesting.
Filed under: Bioarchaeology