A decomposition analogy that may not work

Forensic scientists have long used dead pigs and other animals as stand-ins for humans to better understand how the body decomposes after death. Their research on decomposing animals has informed the views of forensic experts in police investigations.

But recent work by a team of scientists at the University of Tennessee suggests that for anyone trying to draw conclusions about a person’s time of death or the way that decomposition progresses, pigs might be a poor substitute for humans.

The study, conducted at the university’s famed Forensic Anthropology Center, compared the decomposition rates of pigs, rabbits and humans during different seasons. The speed at which the 3 species decomposed differed significantly, the researchers found, and the human bodies varied more in how rapidly they decomposed than the other animals.

“What we’re saying is that to estimate the time since death for human forensic cases, our results indicate that human subjects are the best, because the pigs and the rabbits do not capture the variation we saw in the humans,” said Dawnie Wolfe Steadman, director of the center, who led the research.

Eric Bartelink, a professor of anthropology at California State University, Chico, and the president of the American Board of Forensic Anthropology, said pigs were often chosen for decomposition studies because they had little body hair and their fat ratios were similar to those of humans. “The assumption was that it can’t be that different,” Eric said, referring to the decomposition rate of pigs.

A 2007 study conducted at the Tennessee facility appeared to support that view, finding that a range of insects, choosing between dead pigs and dead humans, showed ‘negligible preference’, suggesting that pigs were not much different from humans in the way they decomposed. The results “confirmed the claim that pig carcasses can substitute for human corpses in research and training programmes,” concluded the authors, led by an entomologist, Kenneth G Schoenly, who is now at California State University, Stanislaus.

But that study included only 1 human and 2 pigs — a very limited sample, as Kenneth and his colleagues noted. In contrast, Dawnie’s research tested decomposition in 15 pigs, 15 rabbits and 15 human bodies (that had been donated to science) that were divided into three trials of five subjects of each species left to decompose in spring, summer or winter. The remains were placed outdoors on the ground at least 10 feet apart at the research facility. The researchers monitored temperature and humidity, and cameras documented scavenging by raccoons or other animals. Insect activity and the degree of decomposition were recorded twice a day.

But Dawnie and her colleagues found that estimates based on a formula often used to calculate time since death correlated weakly with the actual time that the pigs, rabbits and humans in the study had spent decomposing, and that decomposition rates differed sharply among the species and from season to season. In spring and summer, the peak seasons for insects like blowflies that are attracted to carrion, the pigs decomposed more rapidly than the human subjects. But in winter, humans decomposed faster, largely as a result of scavengers like raccoons, which seemed to prefer the human remains.

Dawnie said one of the most striking findings was how much the decomposition patterns of one human body differed from another. “Individuals who have a lot of fat decompose faster than lean individuals,” she said, adding that chemotherapy drugs and other medications could also affect how quickly a body decomposes.