Ageing the Old
Human Skeletal Biologist Simon Mays describes a potential new age-estimation method for older adult skeletons from archaeological sites.
Knowing how long people lived in the past is of fundamental interest for those of us who study earlier human populations. However, we have severe difficulties in estimating accurately age at death from skeletons. For archaeological populations, the best way is using wear on the molar teeth. A problem with this method is that, in the past, people began to lose their molars, due to tooth decay, gum disease or for other reasons, by the time they were middle-aged.
This means that tooth wear cannot usually be used as an ageing method for older people. When a tooth is lost, the bone at the socket and surrounding area is gradually resorbed (removed) so that the height of the jaw in that area becomes less (see photo below). This process continues, apparently at a fairly steady rate, throughout life. In a collection of 19th century Dutch skeletons of known age at death, I found that this reduction in height of the jaw bone where molars had been lost bore a fairly consistent relationship with age in older adults. This suggested that it might be a potential way of estimating age in older people.
This project aims to test this method in another archaeological skeletal collection of known age at death, this time from London.
Testing the new method
A problem with many techniques for estimating age at death is that the rate at which the skeleton changes with age seems to vary in different populations. It is therefore vital to test the new method on different populations in order to see if it is generally applicable, and to study what additional factors might affect its reliability.
The London skeletons used in this project are ideal. The coffins have inscriptions giving the age, name (and hence the sex) and date of death of the person inside. Previous work on the collection has identified individuals suffering from osteoporosis (general loss of bone mass in the skeleton in old age). Using historical sources, parity (number of births) can be reconstructed for some of the women; this might be important as pregancy and breast feeding can have significant effects on bone metabolism.
The specific project aims are to shed light on the following questions:
- In older people, does the height of jaw bones bear the same relationship with age at death in the London skeletons as found in the previously studied 19th century population from the Netherlands?
- Does the relationship differ in males and females?
- Does how many children a woman has borne make a difference to the relationship between jaw height and age?
- Is reduction of jaw height following tooth loss related to overall loss of bone mass with age in the skeleton (osteoporosis) or is it a separate process?
Answering these questions will help to give us a clearer idea of how useful this technique might be for estimating the age at death of older adults from their bones.