Variables aleatorias discretas
Ejemplo 4.2.3. Sea la variable aleatoria X, número de mimetismos que escapan al control, en el experimento realizado sobre mimetismos batesianos del Ejemplo 4.2.1 Definimos la
5.4.1 Preservation
Examination of the preservation of individuals and elements from the Library site sample revealed a starkly different level of preservation between Phase A and Phases B and C. Overall, preservation was good across the sample, which lead to the relative ease of sex and age estimation for individuals excavated from the site. However, the majority of Phase A individuals were poorly preserved, with a low retention of complete elements, so much so that the preservation of the latter was not included in the results presented here. This led to a lack of representation in subsequent chapters relating to the analysis of indicators of health in the sample. On the other hand, individuals in Phase B and C were significantly better preserved, and had a higher rate of element retention, leading to their inclusion in later analyses of health and stature.
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5.4.2 Demography
There was a predominance of female individuals in the sample, though this is not unusual, particularly when viewed in comparison to other samples utilised in the present analysis. A similar predominance of females was exhibited in the two German samples (Jakob 2009), as well as the pooled British sample, also analysed by Jakob (2009) but not included here. In this sample, around one fifth of individuals had not been sexed. Jakob (2009) tentatively argued that those individuals were more likely to be male than female. By breaking down the demographic profile of the Library sample by phase, it becomes clear that the
predominance of females results from a sex imbalance in Phase B, with a male to female ratio of 1:1.7. In fact, as can be seen in Table 5.5 and Figure 5.4, males are the predominant sex in Phase C, at a ratio of 1:0.9. Statistical analyses also found that whilst the differences in frequencies between males and females across all the phases was not significant
(P = 0.069), there was a significantly greater frequency of females for Phase B of the sample (P = 0.016).
There could be a number of reasons for this difference. Firstly, it cannot be discounted that in Phase B the cemetery was divided by sex (gender) and that the area excavated from Phase B predominantly consisted of females. As only an estimated 30-40% of the cemetery was excavated (Anderson 1986) this is a plausible hypothesis. This could also be said for Phase A, but given that 15 of 22 individuals were not sexed, this is more likely a result of poor preservation than segregation by sex. In any case, the sample from this phase is too small to permit comment with any confidence. Following from this, differential migration could also be contributing to this difference. Given that Trondheim was an important trading town, it seems likely that a higher frequency of males were living in the town year round.
Misidentification of males as females or adults of undetermined sex may have also lead to this unbalanced ratio. Sex differences across the skeleton including the skull, usually indicate the smaller and more gracile nature of female individuals (Ortner 2003), and this was likely also affecting determinations of skeletons here. Meindl et al.'s (1985) study into sexing of the skeleton demonstrated that females are not often misclassified as males, but that males can at times be classified as female, or presumably, not classified at all.
Despite of great importance in accurately assessing sex and age in skeletal remains, multivariate analyses can sometimes lead to conflicting sex determinations. This is
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particularly the case when the skull or pelvic bones are not present. Other methods, such as utilisation of the long bone for sex determinations, often result in overlaps across the sexes. Stringent multivariate assessment techniques for determining sex were applied against the samples from Germany and Great Britain, as discussed above, and it was argued that this led to an increase in the number of individuals of undetermined sex and age (Jakob 2009).
This was also an issue for the Library site sample. Care was taken to assess the relative merits of sexually dimorphic traits from the skull, along with the addition of Library site sample-specific long bone sex determinations. However, it is true that in this case, the above issues relating to heavy utilisation of long bones for sex determinations could well have lead to a bias against diagnosing males in particular. Why this may have been the case for Phase B and not Phase C is not altogether clear, particularly given that the number of individuals over 75% preserved was greater in Phase B. Phase B also demonstrated higher retention of the maxilla and mandible than Phase C. It could be that a combination of the above theories could have contributed to this dominance of females in the Phase B sample.
5.4.3 Stature
Stature and other anthropometric measures are sensitive to environmental factors, including nutrition, so are often used as an indicator within bioarchaeology for the environment in which an individual develops, particularly for indicators of stress (Goodman and Martin 2002). Goodman (1991) argues that growth rates are a robust indicator when reconstructing health and stress and that a review of the literature demonstrates that short stature is linked to under-nutrition and/or infectious disease. However, studying the anthropometry of adults does have some disadvantages when compared to the same measurements in subadults. This includes a lessened ability to identify factors affecting growth and size due to decreased sensitivity to environmental variations in adults (Goodman and Martin 2002). However, studies of stature in adults are not vulnerable to the problems that can arise in studies of subadult skeletal remains, particularly those relating to the difficulties of age determination. In an attempt to control for genetic makeup of the populations utilised for discussion here, as suggested by Komlos (1993), only those individuals of European origin were utilised for analysis (with one exception, see Chapter Three).
Within the Library site sample, stature was similar when comparing males from Phase B through to Phase C. Within Phase C, mean female stature decreased by approximately 2
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cm, as did the median value, when compared to Phase B. Whilst this difference may seem important, it must be cautioned that less than half the number of female individuals were available for estimations in Phase C, when compared to Phase B, which could be
contributing to this discrepancy. In addition, two sample t-tests of mean female stature between Phase B and C did not result in a statistically significant difference. However, this small difference could still be indicative of increased physiological stress on females over time, whether it be through nutritional intake or disease.
The economic and climatic changes that occurred in the transition from Phase B to C could have had a negative impact on mean female stature. Low mean stature is well known to be connected to under-nutrition during childhood growth periods (Saunders and Hoppa 1993, Saunders et al. 1993). The greater economic pressure during Phase C, caused by the loss of the stockfish trade and loss of Trondheim's status as the seat of the archbishopric could have led to preferential feeding of males over females during childhood and adolescence. More specifically, males could have been consuming a greater intake of protein during the weaning period, thus leading to lessened stature in female individuals. This kind of preferential treatment can occur even in societies not experiencing food scarcity (Messer 1989), and can have significant consequences for adult stature. The weaning period can also introduce new pathogens to the body and lower children's
immunity due to the absence of their mother's breast milk, which provides some protection against these pathogens. An analysis of the subadults in this population would be beneficial to further elucidate the factors for the reduced height of females.
The mean stature of male and female individuals from the Library site appears to be fairly typical, at least by European standards. The similarities to both Hallow Hill and the German samples are interesting given the differences in period, location and resources. However, despite the differences between the sites, it would seem logical that the high mean statures were related to factors not immeadiately obvious from archaeological reconstructions. Low population density, low pathogen load, high protein intake during weaning periods and a number of other factors not immeadiately measurable are likely to have led to the similarities between the sites.
As discussed previously, work conducted by Koepke and Baten (2005) into stature across location and time in Europe indicates a number of peaks and troughs over the last 2000 years. This research indicated an increase in stature over the 5th and 6th centuries across all regions in Europe assessed, which corresponds to at least part of the periods from which
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both the German samples are dated, and would appear to suggest an environmental cause for an increase in mean stature, rather than a genetic one. Whilst a decline in mean stature did occur in the 7th century, this is only noteworthy in comparison to the large increase that took place in the centuries prior and still may have led to higher than mean stature for both the Nusplingen and Pleidelsheim samples when compared to the other European samples. The high mean statures in these populations could be indicative of this general trend for an increase in stature over the 5th and 6th centuries.
There is a difference between the Library site sample and the later sample from Nidaros Cathedral, with a 3.26 cm drop in mean male stature and 5.02 cm reduction in mean female stature. This is not surprising given the poor health that seems to be evident in this later sample. Hughes (1998) notes that the stature in this sample is lower than in modern Norwegians and, it would appear, also to those of the previous period. She credits this to malnutrition and disease. Levels of osteomalacia and scurvy in the sample indicate an inadequate diet and a lack of availability of fresh food (Hughes 1998). This is also in keeping with Steckel's (2004) work on Northern European stature during the Middle Ages, with mean stature falling to a low in the 17th and 18th centuries, which corresponds to the date for the Nidaros Cathedral sample. However, osteological evidence from the site supports the notion that individuals buried here could have been from a low socio- economic class (Hughes 1998), which could also be contributing to lower mean stature. However, it should be noted that this comparison includes the combined results from Phases B and C of the Library site. Given the decrease in female stature during Phase C of the sample, direct comparisons between Phase C and the Nidaros Cathedral sample would lead to less pronounced differences. This then, would indicate a steady trend over time in Trondheim for decreased mean stature in males and females from Phase B to the 18th century. However, given that those buried in the Nidaros Cathedral cemetery are known to be of a low socio-economic class, and class is unknown for the Library site sample, direct comparisons and inferences regarding a decrease in stature over time are difficult to make definitively.
Kastella had one of the lowest mean statures, but when viewed in context with other stature measurements from Byzantine Crete (Bourbou 2010), this does not appear to be abnormal. The sample was also taken from the 11th and 12th centuries, in the middle of the Medieval Warm period. It has previously been suggested that the LIA was beneficial to the Mediterranean in reducing hot summer temperatures (Koepke and Baten 2005), and perhaps conversely, the Medieval Warm Period was detrimental in this area, leading to an
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increase in temperature and greater pressure on health in the Mediterranean. Conversely, Bourbou (2004, 2010) notes that this was a period of stability, with individuals partaking in a well-balanced diet , with grains supplemented by plants and marine proteins.
Consequently, given the similarities in other mean statures from other samples taken from this region, low mean statures may be related to genetic factors, rather than environmental or social ones.
There is also a visible difference in male stature between the samples taken from the sites of Haffjarðarey and Viðey, both in Iceland. Once again, if stature is used as an index for general population health, this confirms the differences already known about these two towns. Whilst Haffjarðarey is an earlier site, dated to the 13th to 16th centuries, compared to Viðey's dating of 18th to 19th centuries, Viðey was a far larger, more compact town. Despite the fact that those interred in the Viðey sample would have likely been of higher status than the labourers and farmers at Haffjarðarey, the higher population density and size could well have led to higher levels of infectious disease and thus lower stature (Gestsdóttir 2004). It is also possible that, even in light of the lower status, those living in a smaller town would have had better access to a variety of foodstuffs, particularly proteins, important in promoting childhood growth.
These examples of estimated stature from samples across Europe demonstrate that stature estimations cannot be viewed alone as an analogue for health and general well-being in the past. The populations of these samples are dated across a number of centuries, with differing dietary patterns and settlement types. Viewing these means singularly or as a group provides no clear pattern as to the causation of low or high mean statures in these samples. The Library site sample certainly appears to have average to above-average stature compared to others, but it is difficult to discern what factors may have caused this. The relationship of stature to social and environmental factors as well as to other variables such as nutritional deficiencies and infection will be explored further in Chapters Seven and Ten.
5.5 Summary
This chapter has outlined and examined the results of assessments into the age and sex determination of adult individuals from the Library site sample and thus, the demographic profile of the site as a whole and across the main phases. Aspects of preservation were also discussed by phase, as well as stature estimations, which were then compared to mean stature estimations collated from the comparison European samples.
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Examinations of the demographic profile of the sample from the Library site revealed some interesting differences in sex distribution within the phases. Across the samples, the ratio of male to female individuals was not particularly unusual. However, once this was divided into phases, the predominance of females in Phase B became more apparent. It is likely that this was due to a bias in sex determinations, cemetery layout or other factors, such as differential migration.
Preservation of the individuals excavated from the Library site sample was exceptional, with over half of individuals at least 50% complete. The majority of individuals that were less than 25% complete were from the unsexed adult group, which explains the difficulty in determining age and sex for these individuals. Phase A had particularly poor preservation, with the majority of individuals less than 50% complete. The skeletons from Phases B and C were far better preserved, although, there was a slightly higher number of individuals over 50% complete in Phase B.
While male stature was similar when comparing Phases B and C, female stature decreased between these phases, though this was not statistically significant. This could be indicating greater physiological stress for females in Trondheim during Phase B. Chapters Seven (Nutritional Deficiencies and Physiological Stress) and Eight (Non-specific infection) further explore the impacts of infection and nutrition on the sample and seek to determine any differences in health between the sexes.
Stature at the Library site appears to be average to above average, relative to other European samples. Mean male and female stature is higher than in the later sample from Nidaros Cathedral, which is in keeping with a downturn in health during later periods in Norway, but could also be explained by social stratification, with evidence for poorer individuals being interred at the Nidaros Cathedral site (Hughes 1998). The samples from Germany and Hallow Hill have very similar mean statures to one another, despite the differences in date and geographical location. This may be a result of general upswings in mean stature that occurred during the dates from which these samples were taken, or at the very least, suggest that the general health of these groups was good in comparison to other samples in Europe.
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Later chapters will further explore patterns of health in these comparison samples, and the statistical relationship of mean stature from the Library and other samples will be explored in Chapters Seven, Eight and Ten.
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