Recent Changes in the Human Cranium: Reprise

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.
Cranial Measurments
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.
Cranial sutures
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.

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14 Responses

  1. Ok, so various bits of the evidence out there suggest that as human culture/environment has gotten more complex cranial vault heights have increased. Are there any studies where the height has decreased? What are the suggested co-related factors in those studies?
    If we are to assume that vault height roughly equals increased intelligence do we have any idea how fast it is increasing? Has it been a constant rate through time?

  2. My guess is this is due to changes in diet between the period and now. Developmental changes will be affected by lack of nutrients and variety in the diet. We also have a bulk more sugar in our diets than they did, and so have less to build proteins from during crucial phases of development.
    Was there any indication of thinner skulls too?

  3. John – No, they didn’t measure bone thickness. I would suspect dietary changes as well. There is plenty of evidence that eating more processed foods decreases masticatory areas (muscle attachemnts and the size there of, etc) which causes reduced stresses on bone.
    Will – No, the vault height has more to do with lack of stress on the masticatory areas of the skull (ascending ramus of the mandible, etc) as stress decreases due to dietary changes the maxilla and mandible need to generate less force and the skull requires less buttressing so the maxilla and mandile become smaller and become less prognathic. The skull grows higher (the three lines going towards the top of the skull in the diagram) but is not as long from front to back(which wasn’t measured in the article). It really doesn’t correlate with increased brain size or intelligence. I am not aware of any studies that show a decrease…

  4. Further analysis of cranial measurements

    Earlier this week, I wrote about a study published that documented what several scientists observed of changes between human skulls of now and of the recent past. I was skeptical of the results because I thought they did not integrate the variables of eth

  5. I’m curious about your opinion when you compare these studies and the development of Neanderthal morphology. Certain anthropologists state that the intelligence levels and ability for complex spatial thought were limited in the Neanderthals because of lack of vault height even though many specimens are larger in overall volume.

  6. Neanderthals do have a larger cranial capacity than anatomically modern humans. But it’s not a one to one correlation, some areas of their brain are bigger than ours, other areas are smaller – which is where the arguement about intelligence levels and, say capacity for symbolic thought, come from. My own, personal opinion, is that any claims about that kind of thing should be treated with some skepticism.

  7. What about sculpture? Does ancient roman sculpture show any
    difference?
    As a mathematician, I am very dubious of using 17 skulls to prove anything. ( Yes, I know people will argue that such statistical methods are designed for that, and I will say that there are very basic assumptions in those theorems that tend to be ignored by non-mathematicians.)
    Though it is very flattering to think that we are brighter than the people of five hundred years ago, I seriously doubt that we are brighter than NEWTON ( born early 1600’s) or Leibntz or Galileo.
    Case closed.
    Penny

  8. They used a little over 100 skulls in the study…I’m don’t think we could learn anything from sculpture – filtered as it is through peoples’ perceptions and artistic styles.

  9. Ok. 100 skulls is a significant number statistically.
    Still, I don’t think we are generally brighter than people like Newton or Galileo.
    What was the social stratum of these “skulls”? Perhaps, they were really dumb peasants of a type that now would be found only in residental centers for the severely retarded.
    Penny

  10. I’m skeptical that the results have anything to do with increased intelligence.

  11. I’m with afarensis on this one. There’s little to no scientific basis for assuming that vault height correlates to intelligence. I know lots of stupid people with huge foreheads (yes this is a joke).
    Remember that IQ and brain size only have a correlation coefficient of about .50, at any rate.
    Afarensis, I know I sent you the pdf, but I’m too lazy to read the link. DId they mention any data on tooth enamel wear that might give us further clues as to the mastication link? Also, just out of curiosity, is there any evidence that male gorillas (or any male primate really) have relatively shorter vault heights than females?
    Tracy, while I’m not an expert on endocasts of Neandertal skulls by any means (only even seen a handful of papers), I do remember them (and erectus for that matter), having relatively larger temporal lobe areas when compared to us. A good deal of spatial processing occurrs in the medial temporal lobe (including facial and shape recognition, as well as 3d orientation), so I would think that their spatial awareness wouldn’t be much worse than ours if at all.
    Other important areas of spatial awareness are buried too deep wtihin the brain to determine anything from fossils (namely the hippocampus…which is involved in directions and maps and stuff).
    As far as symbolic thought, that’s up for some debate. They do have relatively smaller frontal lobe areas (but again, paleoneurology is not my strength) than we do, but I dont’ remember how large of an absolute difference there is.

  12. IndianCowboy – no they didn’t examine tooth wear. As far as the gorilla’s go…gorillas display a large amount of sexual dimorphism so a male would have a longer cranial vault. The question really is if a female skull were scaled up to a size of the male which would have a longer cranial vault, in other words it’s an issue of absolute vs relative size of the cranial vault. Off the top of my head I do not know the answer to that question and would have to visit a library and do some research to come up with one.

  13. that’s what i was trying to get across, because of the considerable sexual dimorphism in temporalis size, they’d be an interesting test case, if as you said we took into account the size differences.
    don’t worry about the gorilla thing, i’ll just email my old advisor since he did a lot of work in that general area. You want the answer as well?

  14. Yes,
    I would be interested in his answer.

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