Written in bones: Deducing age and sex from skeletons | Human anthropology

 

Drawings of the human skull from Gray’s Anatomy (1858)

Drawings of the human skull from Gray’s Anatomy (1858)

Museum scientists are analysising a collection of human remains from London to learn more about the lives and deaths of  bygone Londoners . A central component of their work is to identify the age and sex of the people they are studying along with any diseases or other pathologies that they had. Here, Rosalind Wallduck explains how anthropologists estimate the age and sex of a deceased individual from their skeleton.

Sex

The skull

The human skull

The human skull

When non-specialists are asked to guess what bones are used in order to deduce the sex of an individual, the skull is not often the first answer given.

Anthropologists study a number of morphological features on the skull which present different degrees of expression depending on whether the individual is male or female.

Although humans exhibit sexual dimorphism, there is not a clear cut divide between male and female skeletons. We accordingly score cranial traits on a continuous scale from 1, being minimal (female) expression, to 5, maximal (male) expression.

  • The nuchal crest is more pronounced and rougher in males than females.
  • The mastoid process (a bony projection behind the ear) is longer and wider in relation to the external auditory meatus (ear canal) in males than females.
  • The supraorbital margin (the upper border of the eye socket) feels sharp and thin in females, blunt and thick in males.
  • The supraorbital ridge (brow ridge) and glabella are larger in males.
  • The mental eminence is more pronounced, the chin is squarer and there is more of an acute angle of the jaw in males than females.

The pelvis

The female pelvis.

The female pelvis.

Due to the mechanical necessities required for childbearing, the shape of the pelvis is a good indicator an individual’s sex. In general, the female pelvis is wider and more angled. Anthropologists also look for some specific morphological features on the bones.

  • There is a greater sub-pubic angle in females
  • There is a broader sciatic notch in females
  • There is subpubic concavity in females, whereas it is absent or minimal in males.
  • There is a sharp ridge down the medial aspect of the ischiopubic ramus in females, which is absent in males.
  • A preauricular sulcus (a notch or depression) is more commonly seen on a female pelvis.

Age

Teeth

Cranium of a child

Cranium of a child, based on dental eruption between 6 and 10 years of age as the canines and second molars are beginning to erupt from the jaw.

Dental development is the most commonly used technique for aging subadult remains given that we know at what age different teeth form and erupt. The rate of these developmental changes also means it is possible to pin down a child’s age within a few years.

But once an individual reaches adult age, getting a precise estimate of age from their teeth is harder to achieve. The degree of dental wear is sometimes used with greater amounts of attrition attributed to older individuals. But this method does have some flaws, as external factors such as a coarse diet can exacerbate tooth wear.

The bones

Childs tibia and fibula

X-ray of a child showing unfused distal tibia and fibula.

Another way that anthropologists can estimate the age of a subadult is to look at the degree of epiphyseal closure. The epiphysis is a cap at the end of a bone which remains separate to the bone’s shaft (or diaphysis) while the bone grows. Over the course of adolescence the epiphyses of different bones fuse at known ages. By examining which epiphyses are closed and which are open, an age estimate can be determined. However once an individual reaches adulthood, all epiphyses have fused and this method is no longer of use other than to indicate the individual was an adult.

Pubic symphysis

Pubic symphysis of a young (left) and old (right) adult. Degenerative changes are clearly visible from the morphology of the surface.

For skeletons of adults, age estimates are achieved by assessing the degree of degenerative bone changes. The pubic symphysis (where the two bones of the pelvis meet at the front) and the auricular surface (where the pelvis articulates to the sacrum) undergo erosive and deteriorating changes throughout the life of an individual. Likewise the articular surface of the sternal (front) end of the fourth rib undergoes degenerative changes over time, such as edge thinning and increasing surface porosity.

From analysis of modern skeletons it has been possible to divide these changes into observable stages with age estimates assigned to each. But as bone degeneration is less rapid than developmental changes, age estimates are also less precise. Consequently estimates of adult age are often categorised as either ‘young’ (20-35 years); ‘middle’ (35 – 50 years) or ‘old’ (50+ years).

by Dr Rosalind Wallduck

Read more

  • London human remains collections
  • Buikstra, J.E., Ubelaker, D.H. 1994. Standards for Data Collection From Human Skeletal Remains.Fayetteville, Arkansas: Arkansas Archaeological Survey Report Number 44.
  • Iscan, M.Y., and Loth, S.R. 1986. Estimation of age and determination of sex from the sternal rib. In: K. J. Reichs (ed.) Forensic Osteology: Advances in the Identification of Human Remains.Springfield, Illinois. Pg 68-89.
  • Meindl, R.S., Lovejoy, C.O. 1985. Ectocranial Suture Closure: A Revised Method For The Determination Of Skeletal Age At Death Based On The Lateral-Anterior Sutures. American Journal of Physical Anthropology. 68, 57-66
  • Todd, T.W. 1920 Age changes in the pubic bone: I. The white male pubis. American Journal of Physical Anthropology, 3: 467-470.
  • Ubelaker, D.H. 1989. Human Skeletal Remains: Excavation, Analysis, Interpretation (2nd Ed.). Washington, DC: Taraxacum.
  • White, T.D., Folkens, P.A. 2005. The Human Bone Manual. San Diego, CA: Academic Press. Pg 360-385.

Funding

The Human Remains Digitisation Project was made possible thanks to the generous support of the Charles Wolfson Charitable Trust.