Maturation of the modern human skeleton

Background: Maturation is the process of becoming mature and reaching the adult state. Maturation occurs in all body systems, but two well-studied maturation processes that occur during modern human growth are skeletal and sexual maturation. Both processes can be studied on dry bone. Variations between individuals and populations are attributed to genetics and environmental influences. Research into maturation can provide new insights into past lives and modern human biology.

Aim: This research examines maturation and development in modern humans using archaeological skeletal collections from England and Scotland. This research looks explicitly at epiphyseal fusion and puberty to determine if the age of occurrence and sequence of these growth events changed between the Iron Age (< 800 BC) and the Post-Mediaeval (1855 AD) period.

Materials: Two hundred and sixty-one skeletons from different periods across England and Scotland were analysed. This included 11 skeletons from Broadstairs (2000 to 350 BC), twenty-four skeletons from Roman Cirencester (69 to 406 AD), thirty-nine skeletons from Anglo-Saxon Chichester, Cirencester, Newcastle, and Auldhame (434 to 1178 AD), one hundred and eighty skeletons from Mediaeval Canterbury, Cirencester, York, and Auldhame (1000 to 1537 AD), and 7 Post-Mediaeval skeletons from Sheffield and Auldhame (1500 to 1855 AD).

Method: An average age-at-death was calculated for each skeleton, mainly from dentition. A stage of fusion (Stage 1: unfused, Stage 2: partially fused, and Stage 3: completely fused) was then assessed for various epiphyses found in the skull, neck, shoulder, elbow, wrist, hip, knee and ankle. Age-at-fusion of each epiphyseal site, order of the fusion sequence and pubertal phase (assessed using selected fusion sites and other elements) were then compared between groupings of skeletons based on social status, archaeological site and time period. Statistical tests were conducted on the data. This included; a goodness-of-fit chi-square to determine if there was a significant relationship between age and fusion, a Mann-Whitney U test to assess significant differences between pubertal phases across the time periods. A binomial logistic regression determined whether age-at-fusion could be distinguished between skeletons of different social statuses. A multiple regression analysis was employed to determine if age-at-fusion could be predicted from multiple variables.

Results: Statistically significant associations between age and fusion indicate four sites (anterior arch and posterior synchondrosis of the atlas, the dentocentral and neurocentral junctions of the axis, and metacarpals 2 - 5, proximal and middle phalangeal epiphyses of the hand) which can contribute to age-at-death estimates for Mediaeval skeletons. Age-at-fusion did not differ significantly between high and low-status skeletons from Mediaeval St Gregory's or when compared between Mediaeval archaeological sites. The cervical vertebrae were the exception.

Skeletal maturation was significantly delated in the proximal radius during the Anglo-Saxon period compared to the Mediaeval period, although several other fusion sites in the Anglo-Saxon appendicular skeleton approached significance. Age at pubertal phase did not differ when compared between the archaeological periods or within the Mediaeval period. Finally, a typical sequence of fusion was discerned: Elbow - (Hip) - Ankle - (Shoulder) - Knee - Wrist. Slight variations in the sequence occurred throughout British history, a similar finding reported by previous research.

Conclusion: This is the first in-depth examination of epiphyseal fusion throughout British history. A key strength of this research is that the same methodology was applied throughout, and therefore comparisons made between data are not influenced by methodological bias. Limited variation in age-at-fusion among the Mediaeval sites is likely due, in part, to similarities in the diet of the sites examined here. Delayed maturation in the Anglo-Saxon period coincided with political and economic unrest that could have affected physical development. Results support the idea that age-at-puberty has only begun to decrease for certain pubertal phases. Only the placement of the shoulder in the sequence of fusion differed in this research compared to previous analyses, and this is likely due to a difference in methodology rather than physiology.