Ageing The Old
Human Skeletal Biologist Simon Mays describes on-going research into 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.
It’s very difficult to accurately estimate age at death from adult skeletons. For archaeological populations, the best way is using wear on the molar teeth. 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. Because of this, tooth wear can usually only be used as an ageing method for younger adults.
New clues for estimating the age of 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 reduces (see the photograph below). This process continues, apparently at a fairly steady rate, throughout life.
New clues for estimating the age of older people at death may come from my analysis of a collection of 19th century skeletons of middle class townspeople from a church at Zwolle, in the Netherlands.
Contemporary sources record their age at death, providing a useful control experiment. I found that the reduction in the 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.
Testing the new method
This project aims to further test this method in another archaeological skeletal collection of known age at death, this time from 18th-19th century contexts at Christ Church, Spitalfields, London.
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. Testing the new method therefore has to include different populations to see if it is generally applicable, and to study what additional factors might affect this method’s reliability.
The London Spitalfields 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).
There are historical sources available that will tell us the number of children borne by some of the women; we’ll use this information as pregnancy 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 the number of 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.
Simon Mays is currently Human Skeletal Biologist for Historic England. He sits on the Advisory Panel on the Archaeology of Burials in England, which he co-founded. He is also currently on the managing committee of the British Association for Biological Anthropology and Osteoarchaeology.
Mays, S: 2015, ‘The effect of factors other than age upon skeletal age indicators in the adult’, Annals of Human Biology, Volume 42, Issue 4, (Abstract available online).
Mays, S: ‘Bone-Formers and Bone-Losers in an Archaeological Population’ , American Journal of Physical Anthropology, Volume 159, Issue 4, Version of article online: 15 DEC 2015.