A metric study of insole foot impressions in footwear of identical 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.
References (26)
- et al.
Differentiating between monozygotic twins through next-generation mitochondrial genome sequencing
Anal Biochem
(2015) - et al.
Emergence of forensic podiatry–A novel sub-discipline of forensic sciences
Forensic Sci Int
(2015) - et al.
Estimation of stature from static and dynamic footprints
Forensic Sci Int
(2012) Estimation of stature from footprint and foot outline dimensions in Gujjars of North India
Forensic Sci Int
(2008)Individualizing characteristics of footprints in Gujjars of north India
Forensic Sci Int
(2007)- et al.
Morphological plasticity in the juvenile talus
Foot Ankle Surg
(2006) - et al.
Reliability of a two-dimensional footprint measurement approach
Sci Justice
(2010) - et al.
Genetic and environmental effects on weight, height, and BMI under 18 Years in a Chinese Population-Based Twin Sample
Twin Res Hum Genet
(2015) - et al.
Birth weight differences in monozygotic twins influence pubertal maturation and near final height
J Pediatr
(2016) - et al.
A genome-wide scan of DNA methylation markers for distinguishing monozygotic twins
Twin Res Hum Genet
(2015)