Age of Skeletal Remains
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.
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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.
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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.
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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.
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