APPENDIX 5.2
STUDYING DEVELOPMENTAL PERTURBATIONS
A consilient theory of pedophilia would be able to account for findings regarding the neurodevelopmental and other biological factors underlying this disorder. Developmental biologists and others who study neurodevelopmental problems have relied on objective measures of developmental perturbations to conduct their research. These measures have the advantage that they do not rely on self-report, and they can be used to estimate the timing of prior developmental perturbations.
Two measures that are particularly interesting for future research on pedophilia are fluctuating asymmetry and minor physical anomalies. For fluctuating asymmetry, morphological traits are generally designed to be bilaterally symmetric so that a feature like index finger length would be the same for both the left and right hands. However, developmental perturbations (due to genetic mutations, transcription errors, environmental toxicity, etc.) can result in bilateral trait asymmetry. This asymmetry is fluctuating because it is randomly distributed; sometimes the left side is larger, and sometimes the right side is larger (in contrast to fixed asymmetries, such as hemispheric lateralization in the human brain or the usual location of human hearts on the left side of the torso). The extent of fluctuating asymmetry across a set of bilateral traits, therefore, reflects the developmental instability experienced by the organism.
Fluctuating asymmetry has been shown to be negatively correlated with physical growth, reproductive success, and longevity in a variety of species (for a review, see Møller & Swaddle, 1997). In humans, men with greater fluctuating asymmetry are rated as less attractive and less sexually successful than men with lower fluctuating asymmetry; importantly, the differences in bilateral symmetry are too small to be perceived by others, so these effects are not explained by a conscious awareness on the part of women that the man is less symmetric.
Minor physical anomalies are small deviations in structure that arise as a result of developmental perturbations. The most commonly studied minor physical anomalies can be observed on a person’s head, hands, and feet. Examples include wide-set eyes, low-set ears, and curved fifth fingers (there are 18 anomalies on the Waldrop scale, which has been used in research on neurodevelopmental disorders such as schizophrenia or autism; Waldrop & Halverson, 1971). These minor physical anomalies are particularly interesting because these structures and the brain are differentiated from the same fetal tissue (ectoderm), and therefore, the number of minor physical anomalies is an indicator of developmental perturbations that occurred in the first and early second trimester and could have influenced brain development as well. Most people have a few minor physical anomalies, but individuals with neurodevelopmental conditions like schizophrenia, schizotypy, autism, mental retardation, and attention-deficit/hyperactivity disorder have more minor physical anomalies, on average, than unaffected controls (e.g., Ismail, Cantor-Graee, & McNeil, 1998; Waldrop & Halverson, 1971; Weinstein, Diforio, Schiffman, Walker, & Bonsall, 1999).
The research reviewed here provides several testable hypotheses about the neurodevelopmental origins of pedophilia. Given the idea that pedophilia is a result of developmental perturbations that affect sexual development, one could predict that pedophiles would score higher than nonpedophiles on measures of fluctuating asymmetry and minor physical anomalies. My colleagues James Cantor and Ray Blanchard are beginning a research project to test this idea with regard to minor physical anomalies.
