Humans-Pigs-Rabbits Decomposition Study to Impact Court Cases Worldwide
New UT research shows humans have different decomposition patterns than pigs and rabbits—a finding that could immediately impact court cases around the world.
For years, forensic court cases worldwide have routinely used animal models to estimate time since death, or postmortem interval, of human remains, largely because access to human subjects was not available. The UT study shows that doing so could yield flawed results because decomposition rates, insect activity, and scavenger activity vary greatly between human and nonhuman subjects.
The study indicates that human decomposition is much more variable than that of either pigs or rabbits.
This study, the first of its kind, was conducted at the UT Anthropology Research Facility, commonly known as the Body Farm. It is the first outdoor laboratory in the world to study human decomposition.
“This research provides guidance to lawyers and judges concerning the admissibility of testimony by anthropologists and entomologists,” said Dawnie Steadman, the project’s lead principal investigator and director of the UT Forensic Anthropology Center, which houses the Anthropology Research Facility.
The work was funded by the National Institute of Justice.
Steadman and her colleagues have presented three papers about the findings to the American Academy of Forensic Sciences and are preparing three articles to be submitted to the Journal of Forensic Sciences.
Lee Jantz and Giovanna Vidoli, associate director and assistant director, respectively, of the UT Forensic Anthropology Center, were co-principal investigators on the project. The FAC team collaborated with Amy Mundorff, assistant professor of anthropology; Jennifer DeBruyn and Sean Schaeffer, assistant professors of biosystems engineering and soil sciences in the UT Institute of Agriculture; entomologist Ralph Williams; and Angela Dautartas, an anthropology graduate assistant who is completing her dissertation using data from the project.
For the study, the researchers placed fifteen of each species of pig, rabbit, and human at the Anthropology Research Facility over three seasons—spring, summer, and winter—to assess decomposition patterns and rates.
The first trial, which occurred in the spring, included five humans, five pigs, and five rabbits. Decomposition of the pigs and humans tracked similarly until insect activity began in earnest about twenty-five days into the test, and then the pigs began to skeletonize faster than the humans. For the rabbit subjects, decomposition appeared to progress slower until maggot activity peaked, and then the process sped up. Significant maggot activity occurred in the lower portion of the body and the skeleton was visible. Just twenty-four hours prior, the same rabbit showed no external signs of decomposition.
In the second trial, which occurred in the summer, pig decomposition occurred more rapidly than that of rabbits and humans and quickly skeletonized by day twelve because maggot activity occurred more rapidly and consumed the pigs more completely than the humans.
In the third trial, which occurred in the winter, there was no insect activity for the first 100 days. During that time, scavengers such as raccoons, birds, opossum, and skunks frequented the study areas. The timing and area of the scavenging activities greatly differed depending on species. The scavengers extracted bits from the pigs and rabbits—such as the fur from rabbits early on—but did not return to them until all five of the humans had been consumed.
“This strongly indicates a preference for the humans over the other species,” the findings state. “With one notable exception, human scavenging begins on the limbs, while the snout and abdomen are the initial preferred scavenging sites on pigs.”
The overall findings indicate that human decomposition is much more variable than that of either pigs or rabbits.
“Now anthropologists and entomologists may be asked in court which studies they used to base their estimate of postmortem interval, and if they are based on non human studies, their testimony could be challenged,” Steadman said.
She noted that pigs can still be useful in answering some questions such as learning what the local carrion insects are and the general baseline patterns of decomposition.
“But we warn that for actually estimating postmortem interval for human cases, then human data should really be used,” Steadman said.