Age is critical information when attempting to identify skeletal remains. How old was the individual when he died, and how long has he been dead?
Two weeks ago, I discussed how a forensic anthropologist determines gender from skeletal remains, and last week, I described how an anthropologist can deduce race and height from an examination of human bones. This week’s post covers ways a forensic anthropologist pins down age. When we talk about age in relation to bones, we must consider two separate issues. First, how old was this individual when he died, and second, how long ago did he die? If you are an investigator trying to determine the identity of skeletal remains, then the answers to both questions will aid you in your investigation.
How old was this person when he died?
When examining a skeleton, a forensic anthropologist considers the processes of growth and decline. Bone growth and tooth emergence can be used to age the skeletons of children, adolescents, and young adults. Once an individual reaches adulthood, his bones stop growing, and his bones, joints, and teeth begin to decline from wear and tear. The rate and degree of decline is far more variable than the process of growth, so anthropologists often struggle to age the skeletal remains of adults.
When we are born, our “bones” are mostly soft cartilage. As we grow, the cartilage is replaced by bone at areas called a growth plate at the end of each bone. Once growth is complete, the growth plates fuse. Infants have more than 300 growth plates which eventually fuse, and since the growth plates fuse and different, known rates, an anthropologist estimates age by analyzing the fused and unfused plates. Teeth also emerge from the gums at a predictable age and provide an accurate estimate of age in juveniles.
Forensic anthropologists can estimate the age of young adults by looking at the skull. When we are born, our skull consists of five flat bones connected by fibrous material called sutures. These sutures allow our heads to expand as we grow, but once we reach adulthood and stop growing, the sutures begin to fuse, and most are completely fused by the time we are 40-years old. If the sutures on the skull have not yet fully fused, then an anthropologist can use them as a rough guide to estimate the age of the individual.
Once bone growth stops and the skull sutures have disappeared, the forensic anthropologist must estimate age at the time of death by studying the degenerative changes in the skeleton. Joints are prone to deterioration, and the pelvis is one of the most common areas used for age estimation. The two halves of the pelvis meet above the pubic area at a joint called the pubic symphysis. This joint undergoes consistent changes throughout a person’s life and can be used to estimate age. Another consistent change in the human body is the cartilage between the end of the fourth rib and the sternum. Over time, this cartilage slowly changes to bone. Other degenerative changes in the spine and joints provide clues to the age of the individual.
I suggest this excellent slideshow for more information on ways to age skeletal remains.
How long ago did this person die?
One of the most difficult questions a forensic anthropologist is asked to answer is how long skeletal remains have been at the location where they were found. If investigators hope to compare the remains to a list of missing persons, they need an estimate of the time since death. Forensic taphonomy is the study of the factors, including environmental factors, which affect decomposition. Biotaphonomy is the study of how the environment affects the decomposition of the body, and geotaphonomy is the study of how decomposition of the body affects the environment around it. Forensic entomology is the study of insect progression on a corpse, and advances in this field now provide researchers with an accurate estimation of the time since the death of a recent corpse.
The post-mortem interval of skeletal remains more than a few years old is difficult to pinpoint. The environment takes a toll on bones. In a hot, dry environment, bones crack over time, while bones submitted to a cycle of thawing and freezing disintegrate into fragments. Recent research has focused on measuring the citrate content of bone for an estimation of the time since death, but results have been varied, and more research is needed. For now, forensic anthropologists often used their best guess from years of examining bones to determine the post-death interval of skeletal remains.
Next week, I’ll touch on other information experts can learn by examining skeletal remains, including what long-deceased populations ate to survive.
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Robin Barefield is the author of three Alaska wilderness mystery novels, Big Game, Murder Over Kodiak, and The Fisherman’s Daughter. To download a free copy of one of her novels, watch her webinar about how she became an author and why she writes Alaska wilderness mysteries. Also, sign up below to subscribe to her free, monthly newsletter on true murder and mystery in Alaska.
