New method for assessing changes in growth and sexual dimorphism in paleoepidemiology

Abstract

This paper has three goals. First, traditional methods used for analyzing growth disruption (GD) and sexual dimorphism (SD) in prehistoric skeletal populations are critiqued. Second, a new method, using adult vertebrae, is presented which helps overcome these limitations. Third, this new method is then tested in the Dickson Mounds skeletal population. Between A.D. 950 and 1300 this population underwent a transition from hunting and gathering (PreMississippian: PreMiss.) to maize horticulture (Mississippian: Miss.). Previous research has found a decrease in long bone length in Miss. children, but no difference in adults, or a change in SD. Could this be due to catch-up growth? In the adult skeleton vertebral neural canals (VNCs) size and vertebral body heights (VBHs) can easily be measured. VNCs generally cease growth by early childhood, whereas VBHs grow through young adulthood. This new method offers inference into prehistoric GD and SD previously thought impossible. For example, if VNCs are reduced, but not VBHs, it implies early GD with subsequent catch-up growth. If both VNCs and VBHs are reduced, GD was presumably chronic. Moreover, within this framework, preadult SD can be examined. Results from Dickson show that early GD was followed by catch-up growth. There was a significant change in SD, with females becoming smaller. They had chronic GD. Miss. males had early GD, followed by catch-up growth. Indeed, Miss. males, compared to PreMiss. males, had significantly larger VBHs. Together, these results suggest females lost, but males gained, social status. Thus, vertebral morphometrics may be an invaluable new tool for paleoepidemiologists.

Non‐specific indicators of stress and their association with age at death in Medieval York: Using stature and vertebral neural canal size to examine the effects of stress occurring during different periods of development

“…This does not affect the nature of the results as Clark and colleagues found that T10 and T11 were amongst the vertebrae whose neural canal growth was stunted by environmental stress. It has been postulated that the AP and TR diameters of the neural canals represent separate growth periods (Clark, 1988). This suggests that the individuals of Fishergate House did not experience environmental stress that was severe enough to disrupt growth during critical periods of AP neural canal development.…”

“…Small VNC size is a non‐specific indicator of stress as it has multiple, non‐specific aetiologies involving malnutrition and periods of infection (Clark et al ., 1985). Whereas catch‐up growth in height can sometimes hide the effects of early developmental stress, the anterio‐posterior (AP) and transverse (TR) diameters (Figure 1; Clark et al ., 1985; Clark, 1988) of the neural canals will remain small as these elements undergo much of their growth in early childhood. At birth they have achieved 65% of their full adult size and by four years of age they are around 80% complete (Hinck et al ., 1966).…”

“…Therefore the potential for growth disruption is greatest in the lumbar spine. The VNCs appear to display this growth curve in both modern and archaeological populations (Clark, 1988).…”

The use of non‐adult vertebral dimensions as indicators of growth disruption and non‐specific health stress in skeletal populations

“…The formation of the anteroposterior (AP) and transverse diameters (TR) of the neural canal is predominantly complete in early childhood, reaching ∼95% of its final size by 5 years of age (Diméglio, 1993). Consequently, evidence of growth disturbance during early postnatal life may become “locked into” these dimensions (Clark et al, 1986; Clark, 1988; Diméglio, 1993; Larsen, 1997; Watts, 2011, 2013a,b). The value of the AP and TR dimensions of the vertebrae has been previously recognized and implemented in both adult (Clark et al, 1986; Clark, 1988; Watts, 2011, 2013a,b) and non‐adult (Watts, 2013b) skeletal collections.…”

“…Consequently, evidence of growth disturbance during early postnatal life may become “locked into” these dimensions (Clark et al, 1986; Clark, 1988; Diméglio, 1993; Larsen, 1997; Watts, 2011, 2013a,b). The value of the AP and TR dimensions of the vertebrae has been previously recognized and implemented in both adult (Clark et al, 1986; Clark, 1988; Watts, 2011, 2013a,b) and non‐adult (Watts, 2013b) skeletal collections. However, these measurements, as well as that of vertebral body height, have yet to be explored as a potential method to map the growth of non‐adults.…”