Pigs vs people: the use of pigs as analogues for humans in forensic entomology and taphonomy research

Abstract

Most studies of decomposition in forensic entomology and taphonomy have used non-human cadavers. Following the recommendation of using domestic pig cadavers as analogues for humans in forensic entomology in the 1980s, pigs became the most frequently used model cadavers in forensic sciences. They have shaped our understanding of how large vertebrate cadavers decompose in, for example, various environments, seasons and after various ante- or postmortem cadaver modifications. They have also been used to demonstrate the feasibility of several new or well-established forensic techniques. The advent of outdoor human taphonomy facilities enabled experimental comparisons of decomposition between pig and human cadavers. Recent comparisons challenged the pig-as-analogue claim in entomology and taphonomy research. In this review, we discuss in a broad methodological context the advantages and disadvantages of pig and human cadavers for forensic research and rebut the critique of pigs as analogues for humans. We conclude that experiments using human cadaver analogues (i.e. pig carcasses) are easier to replicate and more practical for controlling confounding factors than studies based solely on humans and, therefore, are likely to remain our primary epistemic source of forensic knowledge for the immediate future. We supplement these considerations with new guidelines for model cadaver choice in forensic science research.

Keywords: Animal models; Decomposition ecology; Forensic entomology; Forensic taphonomy; Human corpses; Pig carcasses.

Fig. 1

Determinants and general patterns of cadaver decomposition—synthesis based on findings of cadaver decomposition studies (Table 1). Numbers I–V denote general patterns of decomposition (differing according to dominant decomposers, key determinants of decomposition rate and the effect they have on decomposition). Numbers “0” and “1” denote absence and presence of scavengers or insects. Arrows next to rate determinants indicate whether a determinant, considered in isolation, is positively (↑) or negatively (↓) related to decomposition rate. Some determinants in this figure should be considered as sets of simple determinants, e.g. cadaver quality including body mass index, antemortem cadaver modifications (e.g. pharmaceuticals use), postmortem modifications (e.g. freezing during the winter) and others

Fig. 2

Schematic representation of dangers for human/pig comparisons, resulting from intraspecific variation of pigs and humans. Large circles are phenotype spaces (for a species), small circles inside are experimental samples of pigs or humans. The samples can come from anywhere within the phenotype space for the species, but if comparisons are to be made between species, it is desirable that the samples come from the phenotype space shared by both species. Thus, it is possible to design an experiment comparing the same two species and either properly (bottom circles, e.g. large humans versus large pigs) or improperly (upper circles, e.g. large humans versus small pigs) compare the species, depending on the choice or availability of sampled individuals

Fig. 3

Changes in total body score (TBS) during decomposition of pig and human cadavers. Upper panel shows Fig. 2A and 2B from Dautartas et al. [24] displaying results of their trial 1 (Fig. 2A, spring, insects present) and trial 2 (figure 2B, summer, insects present). Lower figure is a modification of Fig. 13 from Matuszewski et al. [59], displaying results of their experiment with pig cadavers of different mass. Red lines in Dautartas et al. [24] are for human cadavers, green lines for pig cadavers. Comparison of the trials 1 and 2 (upper panel) indicates that an increase of difference in cadaver mass between pigs and humans in the trial 2 was followed by larger difference between TBS curves. Moreover, differences between TBS curves in the trial 2 are similar to differences between medium/large and large pig cadavers in the experiment of Matuszewski et al. [59]. Therefore, the differences between pigs and humans in Fig. 2B of Dautartas et al. [24] may be interpreted as the result of differences in mass between the cadavers and not differences in the species of cadaver

Fig. 4

Total body score (TBS) and accumulated degree-days (ADD) with 95% confidence intervals for ADD added and plotted based on data from Table 1 of Connor et al., [23], presented by these authors (as Fig. 1) without confidence intervals. The 95% confidence intervals presented in this figure used standard deviations calculated from coefficients of variation reported in Table 1 of Connor et al. [23]. Red lines—pig cadavers; blue lines—human cadavers