Determining the age of a person from their bones is an important technique used in archaeology, anthropology, and forensic science. The bones that are most useful for estimating age are those that change over time in predictable ways as a person grows and ages.
Bones that change with age
There are several skeletal indicators that allow scientists to estimate the age of a person from their bones. Some of the main bones used for age estimation include:
- Teeth – The development and eruption of teeth follows a predictable timeline in childhood. Teeth also undergo progressive changes with age that can help estimate adult age.
- Ribs – The ribs change in shape and structure over time. In childhood, the ribs have growth plates that fuse by the late teens/early 20s. In adulthood, the rib ends become increasingly porous and pitted.
- Pelvis – The pelvis changes shape dramatically from infancy to adulthood. Key markers are used to determine developmental stages and estimate age.
- Skull – Skull sutures (joints) gradually fuse together over time in a predictable sequence known as ectocranial suture closure. The extent of suture closure can provide an age range estimate.
- Limb bones – The long bones of the arms and legs undergo consistent changes with age. In childhood, ossification centers appear and fuse to the shafts. In adulthood, the joint surfaces decline in quality.
While many bones change with age, teeth and the pelvis tend to be the most useful bones for estimating age throughout life. The sequence and timing of tooth development and wear provides the best clue to estimating age in subadults. For adult age estimation, the pelvis is one of the most reliable bones to examine.
How bones change with age
Bones change in many ways as a person ages from infancy to old age. Here is an overview of the major ways different bones change across the lifespan:
Teeth
Teeth go through several distinct stages of development:
- Tooth formation – Tooth crowns and roots form at predictable times, beginning in utero and continuing through the teenage years.
- Tooth eruption – Teeth emerge through the gums at consistent ages, allowing ages to be estimated in childhood.
- Tooth wear – As teeth are used for chewing, the crowns wear down in a predictable pattern, allowing age to be estimated in adults.
Dentists use tooth formation and eruption to estimate age in children. Forensic anthropologists use wear patterns and microscopic changes in adult teeth to estimate age.
Ribs
Ribs change in the following ways with age:
- In childhood, the ribs have growth plates that ossify by the late teenage years.
- In early adulthood, the rib ends are pristine with well-defined edges.
- In middle adulthood, the ribs slowly become more porous and pitted.
- In old age, the ribs become fragile and less dense.
These consistent changes allow forensic anthropologists to estimate age in adults from the level of porosity and pitting in the rib ends.
Pelvis
The pelvis undergoes profound changes in shape across the lifespan:
- The infant pelvis is small with a rounded birth canal.
- In childhood, the pelvis grows but remains narrow compared to adults.
- The adolescent pelvis widens and deepens as the sacrum expands.
- The adult pelvis reaches its full size and shape, with gender differences emerging.
- In older adults, the pelvic surfaces may deteriorate and osteophytes can develop.
Anthropologists closely examine the overall shape of the pelvis, along with key maturity indicators, to estimate age in subadults and adults.
Skull
Skull sutures fuse in a timeline over decades:
- In early childhood, all sutures are open with no fusion.
- In adolescence, some sutures start fusing from end to end first.
- In adulthood, progressive fusion extends across the sutures.
- By old age, all sutures may be completely obliterated.
Forensic anthropologists study the degree of suture closure across 22 skull sites to estimate age in adult remains.
Limb bones
Arm and leg bones undergo gradual changes as well:
- In childhood, the epiphyses ossify and fuse to the diaphyses following a timeline.
- In early adulthood, the bones are strong and healthy.
- In middle to old age, osteoarthritis and bone loss weakens the joints.
Anthropologists use epiphyseal fusion in the limbs to estimate age in subadults and look for signs of advanced arthritis in older adults.
Key bones used for age stages
While most bones change with age, anthropologists rely primarily on these key bones at different life stages when estimating age:
Infancy (0-2 years)
- Tooth formation
- Skeletal growth and development milestones
Early childhood (3-5 years)
- Tooth eruption sequence
- Rib growth plates
- Limb bone growth
Later childhood (6-11 years)
- Tooth eruption sequence
- Epiphyseal fusion in limb bones
- Pelvic shape changes
Adolescence (12-19 years)
- Tooth root formation
- Epiphyseal fusion sequence in limbs
- Pelvic growth and expansion
Young adulthood (20-35 years)
- Dental attrition
- Rib end changes
- Pelvic shape
- Early skull suture closure
Middle adulthood (36-55 years)
- Advanced dental wear
- Increased porosity of rib ends
- Progressive skull suture closure
- Early joint degeneration
Older adulthood (56+ years)
- Tooth loss and resorption
- Rib porosity and pitting
- Complete skull suture closure
- Osteoarthritis and osteophytes
While many bones help build an overall age estimate, teeth, pelvis, ribs, and skull sutures are the most definitive bones for determining age at different life stages due to their predictable pattern changes over time.
Skeletal vs. chronological age
It is important to note that the skeletal age seen in bones may not always align precisely with the actual chronological age of a person. There is natural variation in how bones mature and change with age across individuals based on factors like nutrition, activity levels, and genetics.
Population specific standards are used to correlate developmental phases in bones to chronological ages. But room for error must be allowed. Bones may develop at different rates than the reference data. Personal life history factors also accumulate over time that can alter the bones relative to a statistical average.
Skeletal age represents biological maturity rather than exact chronological age. Anthropologists use skeletal remains to estimate age ranges that likely bracket a person’s actual age rather than pinpoint an exact number of years.
Methods for estimating age from bones
Anthropologists use a variety of methods to assess bones for age indicators. Some key techniques include:
- Visual assessment – Looking directly at the bone morphology and developmental characteristics.
- Radiographs – X-rays used to visualize development and degeneration in the bone interior.
- Histology – Microscopic analysis of thin bone slices to see cellular features.
- Chemical analysis – Estimating age based on bone mineral content and chemical compositions.
Visual methods based on developmental standards and degenerative changes tend to be the most commonly used techniques for estimating age from bones in anthropology.
Age estimation methods by life stage
Different age estimation methods tend to be used at different life stages based on the available bones and markers. For example:
- Fetal/infancy – Tooth formation, long bone lengths, ossification milestones
- Childhood – Tooth development and eruption, epiphyseal fusion in limbs
- Adolescence – Epiphyseal fusion sequence, pelvic and skull markers
- Young adulthood – Dental attrition, rib end changes, early suture closure
- Middle & old adulthood – Dental wear, rib porosity, advanced suture closure, joint degeneration
Various visual scoring systems have been developed to systematically assess specific age markers on different bones at each major life stage.
Age estimation in older adults
Estimating age becomes more difficult and less precise in older adults. After skeletal maturity, degenerative changes accumulate at different rates in different people based on factors like health, activity, and genetics.
To improve age estimates in older remains, anthropologists may:
- Look for age markers across multiple bones
- Use newer 3D imaging methods to visualize degeneration
- Consider population-specific rates of aging
- Provide wider age ranges rather than point estimates
While age estimation is challenging in older adults, combining multiple indicators of skeletal degeneration can still provide useful clues to arrive at an appropriate age range.
Limitations and debate
Estimating age from skeletal remains has long been a standard practice in anthropology, but recent years have seen more discussion of limitations and ethical concerns, including:
- Population variability – Standards derived from one population may not apply well to another population.
- Secular trends – Bones may mature earlier or degrade differently over decades due to nutrition and activity pattern changes.
- Plasticity – Bones respond to activity and biomechanics, which differ across individuals and populations.
- Statistical age – Estimates represent an average not an individual’s true chronological age.
To address such issues, anthropologists are re-evaluating traditional aging methods and looking for updated approaches based on modern, diverse populations and advanced technology.
Role of age estimation in forensics
Estimating age from human skeletal remains is a critical step in the forensic identification process. Key uses include:
- Focusing the search to compare remains to missing persons of similar ages
- Narrowing down possible matches by estimated age-at-death
- Providing circumstantial support for a presumptive identification
- Indicating whether remains represent one or more individuals based on estimated ages
Being able to provide even a broad estimate of age can aid investigators immensely in making identifications and excluding mismatches. Tight age ranges from well-preserved bones may lead to positive IDs supported by medical records and radiographs.
Some high-profile forensic cases involving age estimation include:
- Establishing victim ages in war crimes investigations
- Aging juvenile remains in abuse or homicide cases
- Separating commingled remains in mass disasters
- Indicating if unknown remains may match historical missing persons cases
By contributing key clues about age-at-death, physical anthropologists provide crucial investigative leads that may help resolve forensic cases involving skeletal remains.
Conclusion
While most bones in the human skeleton gradually change with age, teeth and the pelvis provide the most accurate indicators of age across the lifespan. Dental development tracks growth in childhood and wear patterns reveal aging in adults. The pelvis also markedly changes shape from infancy to old age as it adapts to locomotion and childbirth. Rib ends and skull sutures undergo predictable degeneration as well. Using population-specific standards, anthropologists correlate developmental and degenerative changes in these bones to estimate age ranges. Though limitations exist, age estimation remains an essential tool in anthropology and forensics.
