skull says: bodies and bones

1. Story map

2. Something smells in Tennessee

3. Where the bodies are

4. How to get them to talk

5. The making of a forensic anthropologist

Detail from a copperplate engraving with etching by
Govard Bidloo (anatomist), and
Gérard de Lairesse
(artist), Amsterdam, 1690.
National Library of Medicine, NIH

Bones are the last chance that individuals have to say what their lives were like

skeleton poses with sheetSkin and bones
In the profession's early years, forensic anthropologists worked mostly in labs, and detectives delivered suspicious material -- remains, usually -- by hand. But poking around in the soil where a body is found can tell you a lot about when, and how, a person died.

Crucially, experts can get a first guess at time since death. "Back in the 80s, forensic entomology was the only way to determine time since death after a few days," says Arpad Vass. "Since then, we've developed models that refine what we know about the postmortem interval."

As bodies decompose, they leak five fatty acids -- the breakdown products of muscle and fat -- into the ground. Since the profiles of these acids vary as time passes, analyzing them can reveal how long a body has been dead and pinpoint how long a body has been lying in a particular place. Vass has developed two methods for dating remains by looking at these compounds.

The first traces the ratio of the five fatty acids -- a method that works as long as there is soft tissue (skin and organs) on the body. If not, another technique tracks the ratios of seven inorganic compounds, such as sodium and calcium, which leach into the soil from the bones. If a body is too badly decomposed for those techniques, scientists rely mostly on bones.

We'll get back to bones later, because there's still a lot to do at the crime scene. If the surrounding soil does not contain the telltale chemicals released as a body decays, the body was probably placed there recently. Soil samples containing those chemicals and the bugs that help experts guess how long it has been since the person died. This number can be the key to whether an alibi flies or flops in a murder trial.

Graph shows ratios of fatty acids over time.

Sounds easy enough. But temperature, humidity levels, and grave depth can all change how fast a body decomposes. The fastest transformation from corpse to skeleton at the Body Farm happened in just 12 days. But if a person is buried two feet underground, total skeletonization can take six months, Jantz says. A body six feet under takes more than two years.

A body will also skeletonize faster if it is buried in acidic ground. (Soil in pine forests tend to be far more acidic than soil in deciduous forests.) And "perps," says Vass, are getting better at warping bodies and burial sites to confuse investigators. Vass suspects they learn tricks -- like spraying insecticide on a body to ward off insects -- from TV shows like CSI.

The business of bugs
It creates a big scientific headache when that happens, Jantz says, because bugs make great witnesses. We know we promised to stick to anthropology, but forgive us for a little digression. The American Board of Forensic Entomology lists only eight members, but their work is key in crime-solving.

Only two dozen types of insects eat rotting human flesh. The two stars are the carrion feeders (Calliphoridae) and the flesh flies ( Sarcophagidae). Distinguishing the three larval stages is often the first step in determining how long a body has been dead.

By comparing species found on a body with those in the area, forensic entomologists can also figure out whether a body was moved.

DNA fingerprinting can be used to identify insect species or, sometimes, human content found in their guts. (See "A DNA-based approach..." in the bibliography).

A tale only bones can tell
While a decomposing body, and the bugs that inhabit it, reveal plenty, secrets remain in the bones.

"Bones are the last chance that individuals have to say what their lives were like," says Galloway. "Written into your bones are the things you do repeatedly, the injuries you suffered, how you died, how old you were."

Sometimes a corpse is too long dead to give more information than can be gleaned from the bones alone. Sometimes, only bones remain. And DNA profiling can identify bodies and place suspects at a crime scene. But to identify a body, detectives also need a DNA sample to compare to the remains. Often, too little is known about the body to gauge who it might have been.

Skeletons unearthed in a mass grave.
Mass graves like this are often found years after burial. Investigators rely on forensic anthropologists to glean information from the bones left behind. Courtesy Arpad Vass, Oak Ridge National Laboratory

Enter the bone laboratory. Inside, there are some impressive new tools. But some things -- like cleaning the bones -- will always be macabre, says Galloway.

"We put bones in a box of dernestid beetles -- carrion beetles that will only eat dry, leathery, soft tissue but don't damage the bones at all," she explains.

When there is special urgency or the bugs are busy, Galloway or her graduate students simply boil the bones clean with water and a detergent. "You cook it until you can pull off the soft tissue," she says, recalling an occasion when she accidentally poured a bit of the "soup" in her lap.

Once the bones are clean and dry, the first step is to determine whether they are human. To the untrained eye, bones from deer or goats can be hard to tell from human bones, and it can be almost impossible for anyone but a seasoned osteologist to identify the fragile fragments of a human hand or wrist.

The next question is whether the bones are connected to a crime. The site might be of use to historians or archaeologists but not forensically significant. If so, and the body cannot be identified by DNA analysis, the next step is to create a biological profile.

Looking at the teeth can reveal the age if the remains belong to a child or adolescent. Human teeth break through in a predictable pattern and offer a fairly reliable estimate between five months and 21 years.

The epiphyseal union -- areas of the femur that gradually fuse as a person ages -- can help estimate young ages if the teeth are missing.

The skull and pelvic girdle are two giveaways in determining sex. Male and female skulls show some differences, but the pelvic girdles -- a woman's is wider than a man's -- are the dramatic identifiers of sex.

Scientists guess at stature based on the long bones of the legs, when they are available. If not, a range of height can be established from nothing more than a single finger or foot bone.

Judging ancestry is difficult and controversial. Nevertheless, skeletal attributes, such as the ratios of certain skull bones to one another, can hint at a particular background.

These estimates are far more accurate now than twenty years ago, Jantz says. Part of the Body Farm's mission is to save the skeletons left behind after bodies decompose.

Researchers use the archives (a similar facility exists at the University of New Mexico) to ask questions about how the human skeleton is changing over time.

"The collection now has 500 in it, and it's growing at rate of 50 a year. Ten years will be 1000, if current trends continue," explains Jantz. "There are lots of skeletons of 19th Century Americans, but these are the only modern collections."

The skeletal archives also help researchers devise new methods for creating biological profiles based on bones. "You might have an idea that you think this particular feature would work well as a sexing device or to estimate age or whatever," notes Jantz.

"For our skeletons, we know age, sex, race, height, and you can test your hypothesis about estimating some component of what a person was like in life -- which is the basic activity of forensic anthropology."

Diagram of human skeletonThere are more than 200 bones in the human body. To the trained eye, even the smallest of them can reveal telling details about the person who left them behind. Image: NIH.

Another archive consists of data but no actual bones. In the early 1980s, Jantz and his colleagues initiated a nationwide program that allows anthropologists to record information about their cases -- skeletal measurements, for example -- in a computer database. The database now has information from more than 2,000 skeletons.

"It has the advantage of having considerably more skeletons, but the disadvantage that you can only examine things for which we have data. You can't go back to the skeletons," Jantz says.

Working backwards
You may know about sketch artists who draw pictures of criminals based on witness descriptions. Anthropologists do the same thing using skeletal remains. Forensic artists build models of what a dead person might have looked like by making a plaster cast of the skull and covering it with clay to imitate flesh.

In recent years, computer scientists have been lending a hand. Researchers at the Max Planck Institute for Computer Science in Germany, for instance, have been working on a three dimensional graphics program to produce better likenesses.

Researchers scan a skull to create a 3D computer model. Certain sites on the skull reveal qualities of the flesh that would have covered it. The software automatically adds flesh of appropriate thickness, adjusting for whatever variables -- such as sex, age, and ethnic background -- are already known. The software, which is still in development, uses a template that includes the 24 facial muscles responsible for our expressions, producing an animated head with an almost-lifelike level of detail.

How to do death for a living.

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