HOW OLD WAS THIS PERSON?
As we develop in the womb, grow into adults, and age over the years, our skeletons change in known and predictable ways. For infants and children, this is the appearance and development of skeletal growth areas that spread, meet, and fuse into whole bones. As adults, our skeleton’s growth shifts to maintenance functions, responding to new stresses, such as exercise (or lack thereof) and job-related activities. Our later years bring with them the loss of bone mass, the slowing of our physiology, and the general degradation that accompanies our senior years. These changes are all recorded in our skeletons and forensic anthropologists use these alterations to esti mate a person’s age at death. Estimating age is conceptually different from estimating sex: There are only two sexes, but age is a continuum of 70, 80, or 90 (sometimes more) years. The age-related changes in our skeletons are predictable but not specific enough to allow for an estimate of “31 years and 8 months.” The natural variation within a population and between individuals in a population prohibits a precise determination of age. Esti mated age ranges, bracketed around the most likely age (25–35 years, for example), are the most acceptable way of reporting age at death. This bracketing necessarily leads to imprecision while retaining accuracy, but only up to a point. If an individu al’s age is always estimated to be between 1 and 95 years, those estimates will almost always be correct. That estimate, however, would not be very useful to investigators. By balancing the natural variation in ageing and the anthropologist’s skill with the methods used, an estimate that accurately reflects the precision of the sample and technique can be produced. For the sake of convenience and organization, the range of human ages has been broken into various classes with associated years: fetal (before birth), infant (0–3), child (3–12), adolescent (12–20), young adult (20–35), adult (35–50), and old adult (50+). These classes represent the significant phases of growth, maturation, and decline in the skeleton and related tissues. Bones can indicate the stage of development attained by the appearance and fusion of the various epiphyses throughout the body. Nonunited epiphyses are easy to observe because the diaphyseal surface is characteristically rough and irregular in appearance. Epiphyseal appearance and union occurs over the course of years and is a process, not an event; the degree of union (usually scored on a multipoint scale) must be carefully assessed because this could indicate which extreme of an age range is being observed. The three main stages of union are shown in Figure 1: First, the epiphysis is open; second, the epiphysis is united, but the junction is still visible; and, third, the epiphysis is completely fused. Epiphyses can be small, so every effort should be made during collection to make sure none are overlooked.
FIGURE 1 Different epiphyses unite with the main portion of a bone gradually, so the forensic anthropologist must evaluate the degree of union to correctly estimate age. Epiphyses fuse to the main portions of bone at different times and this pattern of bone growth is an important technique for estimating age in younger individuals.
Although epiphyses all over the body are uniting from infancy onward, the major epiphyses of the bones of modern populations fuse between 13 and 18 years of age. Union typically occurs in the order of elbow, hip, ankle, knee, wrist, and shoulder. Note that the beginning of epiphyseal union overlaps with the end of dental develop ment, and therefore, these two methods complement one another. The last epiphysis to fuse is usually the medial clavicle (collarbone) in the early 1920s. Once all the epiphyses have fused, by about age 28 for most of the population, the growth of the skeleton stops and other age indicators must be used.
FIGURE 2 The face of the pubic symphysis is an important characteristic for estimating age in adults. The surface starts out rugged and bumpy with no defined rim. Gradually, the surface flattens out and a rim develops around the edge of the face. With advanced age, the rim begins to disintegrate although the face remains smooth.
A few areas of the skeleton continue to change in subtle ways (compared with the appearance and union of epiphyses) throughout the remainder of adulthood. The main areas used for estimating adult age are found on the pelvic bones, the ribs, and the continuous remodeling of bone’s cellular structure. These few, relatively small areas of the human skeleton have been intensely studied and restudied over the years by researchers trying to fine-tune the estimation of age at death for adults. Any one method alone, however, runs the risk of misleading the investigator, so all available information must be considered, including physical evidence not of an anthropologi cal nature (clothing, personal effects, etc.). The pubic symphysis (a symphysis is a “false” joint) is the junction of the two pubic bones lying roughly 4–5 in below the navel. This junction is bridged by car tilage that acts as a cushion between the two bones. The symphyseal face shown in Figure 2 is a raised platform that slowly changes over the years from a rough, rugged surface to a smooth, well-defined area. The morphological changes of the pubic symphysis are considered by the majority of anthropologists to be among the most reliable estimators of age at death. This area was first studied in-depth by Todd, who divided the changes he saw into 10 phases, each defined phase relating to an age range. Todd’s work was later advanced by McKern and Stewart, who broke Todd’s holistic method into a sectional evaluation to simplify the process. McKern and Stewart’s work was based on young males who were killed in the Korean War, and this may have unintentionally biased their results; their work was, after all, focused on identifying soldiers of that very same sex/age category. Nevertheless, the McKern and Stewart method held sway for a number of years until Judy Suchey and Allison Brooks began a large-scale collection and analysis project on the pubic symphysis by collecting samples from the Los Angeles County morgue. The intention was to collect a wide-ranging, demographically accurate sample that could be assessed not only for age but also for variations due to an individual’s sex. Their results are more akin to Todd’s than McKern and Stewart’s, although with fewer phases of develop ment (Ubelaker, 1999). Another area of morphological change with advancing adulthood is the sternal end of the fourth left rib. As the cartilage between the sternum and the ribs ages, it begins to ossify at a known and predictable rate. Another method of estimating age at death is the examination of the changes in the auricular surface, where the ilium attaches to the sacrum (the so-called sacroiliac joint). As age progresses, the surface of the bone becomes less bumpy and more smooth, with smallish pores opening up, creating a decrease in the organization of the surface traits. Finally, bone never rests. It is constantly remodeling in response to the stresses placed upon it. This remodeling can be seen in the microscopic structure of bone. In approximately the same way as a wall would be rebuilt, bone first needs to be torn down before it can be built up. This constant erosion and renewal leave perma nent markers in bone: Once we die, these changes cease. Therefore, a correlation exists between the amount of bone reworking and the amount of time the body has expended energy on this remodeling. A thin section of bone is cut, specific areas are viewed microscopically, and the various structural elements (whole osteons, fragmented osteons, interstitial bone fragments, etc.) are counted. Various formulae have been developed and are among the most accurate methods available for estimating age at death. A major disadvantage of this method is that some amount of bone must be removed, which may or may not be allowed because of case requirements.
