When old bones are young
A bone is a bone, right?
Is a bone found at an archaeological dig from a female or male person? Is there a difference? How do you know? It turns out that the determination of biological sex from the examination of a human bone (or a fragment) can be quite challenging.
A person’s skeleton provides a lot of information about who that person was, and while many kinds of bones can help provide this kind of information, the hip bone or pelvis is the most accurate to use for sex estimation.
The trouble is that hip bones look very similar in juvenile male and females. For his doctoral thesis in UM’s department of anthropology, Jose Sanchez wanted to explore how to determine sex from a detailed examination of child and adolescent skeletal remains.
He says: “One thing that was missing from all the studies on the subject was: ‘When do sex differences in the skeleton appear?’ The main assumption has been that these traits develop at puberty and their full expressions do not appear until adulthood. But puberty is not a moment in time during a person’s development; people are not pre-pubescent and then, all of a sudden, post-pubescent. It’s a process with various stages.”
Sanchez decided to address this significant knowledge gap by finding a reliable method of determining at what age visible and measurable sex differences in the pelvis begin to appear and stabilize throughout childhood and adolescence.
To do so, he looked at the skeletons of 128 individuals between four months and 20 years of age, scored observable features that are often used to estimate sex, took accurate measurements of the bones, and applied a number of mathematical processes to the data.
Out of respect for both the individuals he worked with and possible descendants, no identifying information of the deceased was collected for his research. Further, none of the remains included in the study were of Indigenous Ancestry.
Sanchez points out that it is important to recognize the humanity of the remains being used. He explains: “I incorporated traditional care practices, including respectful acknowledgment of the individuals at the beginning and end of the day, and making sure they were protected if they were at my lab bench overnight.”
His findings represent a major methodological contribution to the areas of archeology and anthropology which can help us better understand the lives of those who came before us.
“My research showed that very few observable features in the pelvis appear concurrently in males and females,” he noted. “Most features show a male expression until late childhood or the early teenage years, which is when the female expression appears. But age estimates are not always correct and are unknown for past populations. One constant, however, is the pattern of development during puberty.”
Sanchez discovered that a person must have passed the period of fastest growth during puberty, known as peak height velocity, in order to allow correct sex estimates from looking at his or her bones. He found that using puberty stages can accurately estimate biological sex for juveniles as young as 14 years of age.
He explains: “I wanted to see when, during puberty, areas of the pelvis exhibit sex differences. Delayed puberty can be used as a proxy to understand the environmental conditions people lived in and this can be an indication of adverse living conditions. Through this type of analysis, I hope to share how this transition from adolescence to adulthood was experienced by these individuals.”
Sanchez says his research has significant real-world applications. “This research has important implications for research on past populations since bioarchaeologists can apply this method and confidently estimate the sex of adolescents. By doing so, they can reconstruct the ways males and females experienced this stage of life and determine any similarities and differences in the way they experienced such an important social transition.”
Further, Sanchez says his work has applications for criminal investigations when adolescents are victims of crimes.
He hopes to travel to Europe in the near future to further pursue his work on skeletal remains.
“I want to apply the same idea of tracking when sex differences appear and stabilize to other areas of the skeleton, like the skull and the upper arm bone. The end goal will be to see what area of the skeleton is the most useful for sex estimation of the youngest individuals.”
University of Manitoba Distinguished Dissertation Awards are given to graduating doctoral students who have been nominated by their faculty/college/school for a dissertation that represents a ground-breaking piece of original work. Each year, one award is offered in each of the following categories: applied sciences, health sciences, humanities, natural sciences, and social sciences. Awardees receive a $3,000 prize.