A metric study of insole foot impressions in footwear of identical twins

https://doi.org/10.1016/j.jflm.2017.09.005Get rights and content

Highlights

  • Analysis of quantitative measures of foot impressions in the footwear of identical twins.

  • A total of 17 length and breadth measurements were taken of each foot impression.

  • A combination of the Reel Method and Extended Gunn Method was utilized.

  • Study observations are likely to aid in forensic investigation of cases involving foot impressions of the twins.

Abstract

Foot impressions are of utmost importance in crime scene investigations. Foot impressions are available in the form of barefoot prints, sock-clad footprints, and as impressions within footwear. Sometimes suspects leave their footwear at the crime scene, and the insole of this footwear may contain the foot impression of the suspect which may be important evidence linking him or her to the crime. The task of identification based on the analysis of footprints can be challenging when the footprints belonging to one of the identical twin is available for examination. The present study is based on the quantitative measures of the foot impressions in the footwear of adult identical twins. The study was conducted on four sets of female monozygotic twins from the United States of America. A total of 17 length and breadth measurements were taken on each foot impression. A combination of Reel Method and Extended Gunn Method was utilized to produce the measurements. The measurements of the foot impressions were compared among the twins on the right and the left side. Differences were found in the various footprint measurements among the twins. The study's sample size was not large enough to apply robust statistical tests, but the study is significant in that it presents the first detailed comparative analysis of a large number of measurements of insole foot impressions of adult twins. The observations derived from the study are likely to assist forensic investigations in cases involving the foot impressions of the twins.

Introduction

Monozygotic twins or identical twins are derived from the same fertilized egg, which contains the genetic set consequent from the combination of the chromosomes of mother and father. The twins may look alike, however, upon closer examination, their physical structure, characters, and features are not always the same.1, 2 Differences in the identical twins have been attributed to the environmental influences which begin with the early environment in the mother's womb and continue in the external environment after birth. However, many recent studies contradict the belief that the distinctiveness in the identical twins has only been attributed to the environmental influences; their genomes may also show variations.3, 4 This contention suggests that their DNA may differ at various points in their genomes, which are referred to as epigenetic differences. This epigenetic variation is indistinguishable in monozygotic twins during early life and becomes much more apparent in later life.5, 6

The significance of human foot and footprints in forensic sciences and crime investigations has been studied extensively.7, 8, 9, 10, 11 The morphology of the human foot is influenced by epigenetic expression and environmental factors, and the human foot is considered to be a phenotypically highly plastic structure.12 This plasticity allows for changes in the foot morphology and biomechanics, and is influenced by such environmental factors as footwear use13 and an individual's weight.14, 15 Research has investigated the use of insole impressions in footwear to exclude or link a suspect to the scene of a crime.16, 17, 18 The use of insole impression evidence may form the basis of identification in cases where footwear is recovered from a crime scene,19, 20 which may occur when a suspect hastily leaves his or her shoe behind. In addition, forensic studies on bare footprints have shown variations in the footprints of identical twins.21, 22, 23

The present study is based on the quantitative investigation of the insole foot impressions in the footwear of identical adult twins, and attempts to study the quantitative similarities and dissimilarities in measurements of insole foot impressions in the footwear of identical adult twins. Generally, there is a greater similarity between individuals who are monozygotic twins than those who are not twins; and thus, the question of differences in the insole impressions of twins has heightened importance. Further, this study will have implications in criminal investigations and forensic scenarios where the identical twins are involved.

Section snippets

Participants

The study sample comprises of four sets of female adult monozygotic twins (eight adult females) aged between 26 and 54 years of age from the United States, each considering themselves to be classified as Caucasian. Right and left shoe insoles were collected from the study participants. A total of 17 length and width measurements were taken on each sole (34 measurements for each individual on both soles) using standard landmarks and techniques, which were subsequently analysed.

Landmarks and techniques

The measurements

Results

Various insole footprint measurements in the twin groups revealed differences in measurements between them on the left (Table 2) and right sides (Table 3). The differences in sole measurements also existed when compared between the right and left sides (Table 4). Box Plots for the various length and width measurements to show the distribution and median values among the two groups of twins is depicted in Fig. 2, Fig. 3, respectively. Variability in the sole measurements is apparent between the

Discussion

Several foot impression analysis methods have been advanced for comparison and identification purposes. Common methods include the Gunn Method, the Gunn Extended Method, the Optical Center Method, and the Overlay Method.18 A more recent method, the Reel Method, has met requirements for reliability and validity.25

The Reel method uses length, width, and angular measurements and has been shown to be reliable for 2D footprint comparison.25 The Reel method establishes a central axis by bisecting a

Conclusion

The present study has been conducted on a rare sample of monozygotic twins. The study concludes that quantitative differences are found in the insole foot impressions of the footwear of identical twins. Although, the study is based on a small sample size, it significantly contributes to the literature as it presents the first detailed comparative analysis of a large number of measurements in the insole foot impressions of identical adult twins. The observations from this study are likely to

Acknowledgements

The authors thank Sarah Reel for permitting the use of Fig. 4, Reel's method of measurement, from her PhD thesis.

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