What is Forensic Anthropology?

First off forget anything you THINK you know about forensics. CSI? BULLSHIT. Bones and NCIS are the closest on tv you will EVER find so far. And even then they get some things wrong so don’t think you know more than the experts do, because you don’t.

Forensic Anthropology is the field of study that examines human skeletal remains that result from unexplained deaths. Forensic Anthropologists are experts in skeletal biology and they examine human bone to extract as much information about the person as possible.  In this regard, there are five main goals that are attempted to accomplish:

1. Determine ancestry, sex, age, and living height.
2. Determine the nature of trauma and injury.
3. Estimate a postmortem interval. The time since death is impossible to accurately determine especially after 3 days plus it gets tricky and decomp will depend on area and environment.
4. Locate and recover buried remains. Usually there is a lot of help in this aspect; usually there is only one forensic anthropologist in a city, only about 100 throughout the United States. When mass burials are found people can be called in to help excavate the graves, usually people with some medical training. Local police are now being trained or retrained to know the difference between human and animal bones.
5.  Obtain a positive identification of the deceased. This is sort of the whole point isn’t it? Without a positive proof of death a family will have to wait seven years before they can get a report of death and claim insurance or inheritance. This among other reasons is why this job is so important.

Generally a forensic anthropologist doesn’t leave the lab. They have people to go out to the scene to take pictures or to gather information.  They do attempt to provide as much information as possible to law enforcement officials, including information about the deceased as well as information about the circumstances surrounding their death. The most important of these questions where synthesized by Dr. Clyde Collins Snow;

1. Are the remains human? Are they of medicolegal significance (i.e. no more than 50 years have passed since death)?
Most police can now tell human from animal bones, but a lot of people cannot. Small bones or bones that are found by pets are   frequently brought in to be looked at. If you EVER suspect you have found human bones DO NOT touch them or disturb the area and call the local police. A horse’s tibia (leg bone) and bear feet look remarkably like human leg and feet bones, it is better to be safe then sorry. Any bones that are too old (e.g. prehistoric) can be eliminated from further forensic analysis.

2. Do they represent one individual or several?
You will hardly ever find a skeleton where every part is in it’s place. They are more found in a jumble, but thankfully bones that belong to the same person will fit together and you will be able to tell when you have more than one person.

3.  When did death occur? 

4. What was the decedent’s ancestry? 
Many methods for determining sex, age and stature require knowledge of ancestry to be properly applied. This is why this question has been moved from it’s original position of #6 to where it is now. Since the word race engenders too many negative connotations especially among professional anthropologists the term ancestry is coming into wider use. It should be known to the general public as race or ethnic group.

5. What was the decedent’s sex? 
Males of Asian ancestry often have more “female-looking” skulls than those of European ancestry.

6. How old was the decedent?
It is pretty easy to tell a child’s age but older like between 33 and 35 the skeleton doesn’t change enough between those ages that would make it stand out.

7. What was the decedent’s stature? body weight? physique?
Weight can be pretty easy to determine, stresses on particular bones tell many tales.

8. Does the skeleton (or body) exhibit any significant anatomical anomalies, signs of old disease and injuries or other characteristics which, singly or in combination, are sufficiently unique to provide positive identification of the decedent?
Old injuries like a broken bone when you were ten, when properly set at the time of injury will not be easily if at all seen if you die at 35.

9. What was the cause of death?

10. What was the manner of death?
Usually the forensic anthropologist isn’t too overly worried about this one and answering it can be quite situation dependent.

Data Gathering.

Mostly laboratory methods are used to gather data on a skeleton
Anthroposcopy: using microscopes
Osteometry: measuring things
Metric methods: Lots of these give information on male/female/age/height/etc. There are a ton of measurements that can be done on a skull alone.
Chemical methods: Many tests can be  run for poisons, drugs or disease.
Histology:  Thin slices of bone under a microscope.

Forensic anthropologist use all means they have available to them which takes time, quite a bit more than the thirty to fifty minutes it takes CSI: Miami, New York, whatever to figure out everything. You may or may not have seen some of the methods used in real life, but here they are, pictures and text are from my text book so respect the copyrights.

Data Analysis.

Mostly statistical methods used to determine where in the population the skeleton falls.
Decision tables: majority rules.

Decision Table

An example of a decision table.

This is the simplest method for deciding between conflicting information. In this technique, the various decision options are listed across the top of the table, while the characteristics for determining these options and listed down the side. The user marks those columns where the characteristic indicates agreement with one of the options; and the column with the most marks represents the decision that is most likely to be correct.

As example; say you are given a skeleton and asked to determine if it is contemporary (i.e. could be of medicolegal significance) or noncontemporary. A number of characteristics of bone can aid in this determination, these are listed down the left side of the table above, while the options (i.e. contemporary and noncontemporary) are listed across the top. In each of the columns, the expression of the characteristics within each option is listed. Contemporary skeletons are usually light in color (i.e. color of fresh bone), whereas noncontemporary bones are often darkened by the soil in which they were buried. Similarly the surface texture of contemporary bone is usually smoother than bone that is older.

Range Charts: How to combine several sources of information to arrive at a single estimate.
Range ChartThe age at death of a decomposed body is to be assessed from skeletal data; there are various methods for determining this parameter. Your skeleton exhibits fusion of the growth center at the end of the clavicle (collar bone) where the sternum (breastbone) attaches. Since we have previous studies on growth we know that this indicates an age at death of 21 to 30 years with an average around 28. We also know that the lines that separate the various bones of the skull (suture lines) fuse and disappear over time and the state of fusion for our skeleton indicates an age of 18 to 44 years with the average of 31. Then we look at the pelvis which indicates an age of 25 to 29 years with no average.

Now we have a skeleton that we know was 18 to 44 years of age when they died. Run that through any missing persons data bank and you’re going to be sifting through people for months. So to determine the most likely age at death we first must draw a time line that states at the lowest value of the ranges given, in our case that would be 18, and ends at the highest; for us that’s 44. We mark the ranges for each of the data sources (clavicle, skull, and pelvis) as vertical bars and mark averages as horizontal crossbars.

Simply look at the areas of overlap between the various ranges and the most probable estimate can be made Our skeleton is in the mid-to-late-twenties. Run that through missing persons and you get a smaller group of individuals.

Indexes: Simple and yet powerful statistics for quantifying anthroposcopic traits.
IndexesWhen two measurements express visually identifiable characteristics we can divide one into the other to obtain a single number, then multiply by 100 to get an index. The values of indexes vary among groups, so calculating the index on an unknown skeleton can lead to a determination of group membership.

The nasal index (shown above) is a great example. It is calculated by dividing the width of the nasel opening of a skull with the height of the nose then multiplying the result by 100. African descent people generally have wide noses so the resultant index usually is 85% or higher. Which means that the nose is almost as wide as it is high. European descent with their narrower noses generally have indexes that are less than 70% so if we have a skull with a measured index of 90% would most likely point to African descent.

Discriminant Functions: These use any number of measurements to distinguish two or more predetermined groups.

Discriminant functions

Most famous application of this method in biological and forensic anthropology was by Eugene Giles and Orville Elliot (1962), they used a number of measurements of the skull to distinquish ancestral groups from each other. They calculated discriminant functions from measurements of samples of Whites and Blacks from the Terry Collection and of Native Americans from the Indian Knoll archaeological site. These functions are still used today.

Regression Equations: Predicting the size of one characteristic from the size of another.

Regression Equations

The most popular method of all data analysis methods. The idea came about when Sir Thomas Galton in his studies of inheritance thought he saw that children shared characteristics with their parents but to a lesser degree, as in children were shorter in statue than their parents. The term regression toward the mean was used to characterize this phenomenon. Outcome has since been disproved, but the term has endured.

The image above presents a plot of the length of the inside bone of the foot (metatarsal 1) against stature for 22 Africans of both sexes. Longer foot bones are associated with taller people as seen in the plot points on the upper right. The equation of the line that best fits the relationship between metatarsal 1 length and stature is

Stature = 51.85 + 1.799 (length of meta 1)

We can use the first bone in a foot to calculate the height of a person. Example, my metatarsal 1 is 60 mm so it’ll look like this:

stature= 51.85 + 1.799(60) = 51.85 + 107.94 = 159.79 cm which translates into 5 foot 3 inches.

But because regression are based on samples, they contain three error sources: value in first equation of 51.85 (intercept) is only one of many such values. Other samples might yield different or similar values. The slope value (that’s the 1.799) is also only a approximation of any number of possible slopes. If you notice that none of the data points fall on the regression line however by calculation the predicted value always will land on a regression line.

Until next time, stay warm, have fun and watch out for life.

Categories: Anthropology, Forensics | Tags: , | Leave a comment

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