/ 17 June 2024

How decomposed pigs could help identify human remains

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A new study conducted on decomposed pigs provides insights into identifying human remains using cutting-edge technology.

The research was conducted by Kara Adams as part of her PhD dissertation at the University of Cape Town (UCT). 

Adams said she undertook the study against the background of the fact that human remains are often found in a state of decomposition after a crime, making them hard to identify and severely hamstringing the forensic investigation.

However, the use of human bodies in taphonomy — the study of how organisms decay and become fossilised — is not allowed in South Africa, so Adams made use of the next-best alternative — large pigs. 

“My research, conducted on pig bodies as a proxy for humans, contributes to criminal forensic analysis by creating baseline data on how clothing affects decomposition and scavenging in different habitats,” she told the Mail & Guardian.

Pigs are regularly used globally as a stand-in for humans in studies, because of their anatomical similarities to us.

Adams’s two-part study forms part of UCT Professor Victoria Gibbon’s ongoing forensic taphonomic research into the effect clothing has on the decomposition process of dead bodies. Adams dressed six dead pigs, which weighed 60kg each, in clothing, including cotton T-shirts, underwear, denim jeans, leather belts, socks and shoes, which are often used in local medico-legal cases. 

“By understanding the typical decomposition rates of clothed versus unclothed remains in specific environments, using pigs as a model, forensic experts can more accurately estimate the time since death for human decedents,” she said. 

Two of the pigs were placed in the peri-urban habitat of Delft in the Western Cape and four in suburban Rosebank in Johannesburg to compare the decomposition process under different climate conditions. 

“These results advocate for using single, clothed porcine bodies, deployed across multiple seasonal trials in forensically significant locations to produce data that can be considered forensically realistic,” Adams said. 

She observed the decomposition of the pigs’ bodies over 18 months between July 2021 and March last year to draw her conclusions.

The examination was conducted through an autonomous weighing apparatus developed and designed by Adams’ supervisors, Gibbon and Dr Devin Finaughty, in partnership with Justin Pead from UCT’s electrical engineering department. 

The apparatus automatically recorded the weight of each pig every evening, while cameras were placed around the carcasses and monitored any scavenging activities.

The first part of her study showed that the decomposition process was delayed significantly during the winter season and expedited in summer. This, Adams said, meant that clothing types and seasonal changes can affect decomposition.

“In warmer conditions, decomposition tends to occur more rapidly due to increased microbial activity and the presence of insects that accelerate tissue breakdown,” she said.

At the peri-urban research site in Delft, a mongoose played a role in the porcine bodies’ swift decay.

“The scavenging by the Cape grey mongoose accelerated the decomposition process in Delft. In Rosebank there was no mongoose present, which means it took longer for the porcine bodies to start decomposing,” Adams said. 

The second part of her study, which involved the precocious mummification process, showed how time and temperature affect decomposition and that the moisture in the skin of the pigs could determine how long they had been dead. This is mummification that takes place in less than a month. This part of the research required Adams to use printed computing boards that were inserted into each carcass’s tissue to measure and record the moisture content in 15-minute intervals. 

The results were analysed using data that included environmental conditions, such as temperature and rainfall, to help her establish how they could influence the drying process of the pigs’ tissue.

“This research provides valuable insights [into] desiccation in the summer, which appeared to follow an exponential decline, and temperature was the most influential environmental factor. 

“These data demonstrate the potential of using accumulative degree days and moisture content to estimate the post-mortem interval,” Adams said.

A similar study, which was conducted in 2020, found that the decomposition of human and pigs’ bodies differs in terms of their effect on soil biogeochemistry and microbial decomposer activities, “adding to our understanding of decomposition ecology and informing the use of non-human models in forensic research”.

Adams hoped her research would contribute to forensic taphonomy.

“These data aim to improve identification and forensic investigative leads and contribute to the improvement of time-since-death estimation accuracy,” she said.

“They also deepen our understanding of taphonomic processes in the region’s unique environments, leading to more precise forensic reconstructions and aiding in the development of region-specific forensic models and protocols.”

Commenting on Adams’ research, Gibbon said understanding the nuances of local decomposition would  help authorities in developing forensic leads.

“By determining the season of death it can be informative for probable identification leads during the investigation, knowing the patterns of scavenging can help with body recovery and identification and knowing the impact of scavenging on decomposition rate is informative for determining a rough timeline,” she said.