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When excavating human remains, archaeologists are sometimes able to identify a pregnant woman if the bones of her unborn child are still present in her pelvic area. There are many reasons why this might be missed, however, such as if the skeletons have degraded, the grave has been disturbed, or where foetal bones are misidentified. It is also impossible to recognise pregnancy in cases where a mother died and the baby survived, or where they were not buried together. In this month’s ‘Science Notes’, however, we look at recent research (published in the Journal of Archaeological Science) that has been able to detect the presence of several hormones – including progesterone, which rises significantly during pregnancy – within human bones and teeth for the first time, opening up the possibility of future studies being able to look more precisely at reproductive histories in past populations.
An interdisciplinary team from the University of Sheffield set out to see if a protocol could be established for identifying hormones, particularly sex hormones, within human skeletal tissue. If successful, it would be the first time that sex steroid hormones have been found in either modern or ancient human teeth and dental calculus, as previously only oestrogen and testosterone had been identified in hair and bone samples. As the archaeological survival of hair is not common, the ability to detect hormones within bone is essential in order to recreate whole population histories. So, in order to establish a technique for their own analysis, the team looked to recent research in marine mammals, which had identified hormones within teeth and tusks to great effect.
Applying these methods to human remains, they tested samples from three men and seven women from four different cemeteries, ranging in date from the 1st to 19th centuries AD. Of the women, two were found with foetal remains in utero, two others had been buried with newborn remains in the same grave, one was known to have had a pregnancy in the past (aDNA analysis has identified one of her children, aged between 10-12 at the time of death, from the same cemetery), and the histories of the last two were unknown. The team took samples from bone, as well as from molars and dental calculus (plaque build-up around the teeth). These were then pulverised, and the powder incubated in methanol, centrifuged, and finally dehydrated. The resulting ‘supernatant’ was reconstituted to be analysed using enzyme-linked immunosorbent assay (ELISA).
This analysis revealed that oestrogen, progesterone, and testosterone were present in measurable concentrations in bone, as well as in the dentine, enamel, and roots of molars. The team also found that progesterone and testosterone could be found in dental calculus. For the two women with pregnancies in utero, no testosterone was detected, but one had elevated progesterone in her bone and dental samples; she was the only individual within the study where oestrogen was detected in the bone, too. For the two women who were buried with newborn remains external to their bodies, elevated progesterone was found in their dental calculus and no testosterone was detected in their bones or teeth (although one did have testosterone in their dental calculus, perhaps reflecting circulatory levels during pregnancy). Overall, these results suggest that high progesterone levels in teeth and dental calculus, the presence of oestrogen in bone, and a lack of testosterone in hard tissues may be taken to indicate pregnancy at the time of death.
Going forward, the main point of future research is to elucidate further the pathways along which these hormones are entering the hard tissue because, although they have been detected, it is unknown when they are incorporated into these structures and how long they remain there. There may also be various ways in which each hormone is deposited and accumulated across multiple pregnancies. Understanding this process is crucial to being able to interpret the different concentrations of hormone seen within each type of tissue and what they mean for identifying not only pregnancy but possibly puberty and menopause as well. With the conclusion of this project and the identification of a new protocol for identifying pregnancy in skeletal remains, possible new avenues of research have been opened that seek better to understand women’s life histories in the past.
Text: Kathryn Krakowka / Image: Dr Hugh Willmott, University of Sheffield
