The study of skeletal and dental remains is a key tool in understanding ancient human societies, but conventional methods for determining the sex of individuals are not always reliable. The oldest and most widely used method is based on the anatomical differences between male and female skeletons, but these can only be applied to adults and are only reliable for populations that can provide large enough samples for compiling statistically reliable tables. Worse, these anatomical methods are almost worthless when dealing with bone fragments.
A more modern method is through DNA fragments that can be studied to find sexual markers. However, preserved and uncontaminated DNA is notoriously difficult to retrieve from archaeological sites even with techniques like Polymerase Chain Reaction (PCR), which can “photocopy” tiny samples of recovered DNA for analysis. Even then, DNA degradation due to time and environment can affect its reliability as a sex indicator.
Led by postdoctoral researcher Tammy Buonasera, the UC Davis team worked with remains excavated from two ancestral Ohlone villages near Sunol, California, by the Far West Anthropological Research Group of Davis in collaboration with the Muwekma Ohlone tribe. Instead of looking at taxonomy or DNA, the scientists extracted the protein amelogenin from the tooth enamel. Amelogenin is produced by the splicing or splitting of the AMELX gene on the X chromosome in females or AMELY gene in males on the Y chromosome during the process of amelogenesis, which is the development of tooth enamel.
By studying the sequence of 20 amino acids that make up the protein, the team could work backwards and determine the DNA code that created the protein and therefore the sex of the person from whom the tooth was taken. According to the researchers, the new method was more reliable than anatomy or DNA, which only worked in half the cases. In addition, the protein method worked on the remains of children.
The results were published in Scientific Reports.
Source: UC Davis