Human teeth and fingerprints have similar embryological origin from epithelial-mesenchymal interactions. This study aims to determine the nature and extent of sexual dimorphism in fingerprints and teeth of twins; investigate the influences of genetic, epigenetic and environmental factors on observed variation; identify possible developmental associations between the phenotypes; and explore whether both systems display the features of complex adaptive systems. Mesiodistal (MD) measurements from both primary and permanent teeth and ridge density (RD) from three different finger areas, namely ulnar (U), radial (R), and proximal (P), from fingerprints of the same set of monozygotic and dizygotic Australian twins (28 males and 31 females aged 8 to 10 years, and aged 13 to 16 years, respectively) were collected and analysed. Sexual dimorphism was observed in both the primary and permanent dentitions, with the latter showing greater magnitude of differences than the former. There was no observed sexual dimorphism in the fingerprints of the 8 to 10 year cohort, but a few finger areas (left index U, right index R, left little R, and left little P) of the 13- to 16-year cohort exhibited significant differences, showing that friction ridges expand over time. It was concluded that both dentition and dermatoglyphics display characteristics of complex adaptive systems.
complex adaptive system, dentition, tooth size, dermatoglyphics, fingerprints, human development, mesiodistal, ridge density, sexual dimorphism
 Moorrees, C.F.A., Thomsen, S.O., Jensen, E. & Yen, P.K., Mesiodistal crown diameters of the deciduous and permanent teeth in individuals. Journal of Dental Research, 36, pp. 39–47, 1957.
 Ribeiro, D., Sampson, W., Hughes, T., Brook, A. & Townsend, G., Sexual dimorphism in the primary and permanent dentitions of twins: an approach to clarifying the role of hormonal factors (Chapter 5). New Directions in Dental Anthropology: Paradigms, Methodologies and Outcomes, eds. G. Townsend, E. Kanazawa & H. Takayama, University of Adelaide Press: South Australia, pp. 46–64, 2012.
 Garn, S.M., Lewis, A.B., Swindler, D.R. & Kerewsky, R.S., Genetic control of sexual dimorphism in tooth size. Journal of Dental Research, 46, pp. 963–972, 1967. http://dx.doi.org/10.1177/00220345670460055801
 Acree, M.A., Is there a gender difference in fingerprint ridge density? Forensic Science International, 102, pp. 35–44, 1999. http://dx.doi.org/10.1016/S0379-0738(99)00037-7
 Taduran, R.J.O., Tadeo, A.K.V., Escalona, N.A.C. & Townsend, G.C., Sex determination from fingerprint ridge density and white line counts in Filipinos. HOMO - Journal of Comparative Human Biology, 2015.
 Nanci, A., Ten Cate’s Oral Histology: Development, Structure, and Function, 7th edn., Elsevier Health Sciences: Missouri, pp. 16–107, 2008.
 Kücken, M. & Newell, A.C., Fingerprint formation. Journal of Theoretical Biology, 235, pp. 71–83, 2005. http://dx.doi.org/10.1016/j.jtbi.2004.12.020
 Brook, A.H., Brook O’Donnell, M., Hone, A., Hart, E., Hughes, T.E., Smith, R.N. & Townsend, G.C., General and craniofacial development are complex adaptive processes influenced by diversity. Australian Dental Journal, 59S, pp. 13–22, 2014. http://dx.doi.org/10.1111/adj.12158
 Guatelli-Steinberg, D., Sciulli, P.W. & Betsinger, T.K., Dental crown size and sex hormone concentrations: another look at the development of sexual dimorphism. American Journal of Physical Anthropology, 137, pp. 324–333, 2008. http://dx.doi.org/10.1002/ajpa.20878
 Alvesalo, L., Human sex chromosomes in oral and craniofacial growth. Archives of Oral Biology, 54S, pp. 18–24, 2009. http://dx.doi.org/10.1016/j.archoralbio.2008.06.004
 Dempsey, P.J., Townsend, G.C. & Richards, L.C., Increased tooth crown size in females with twin brothers: evidence for hormonal diffusion between human twins in utero. American Journal of Human Genetics, 11, pp. 577–586, 1999.
 Ribeiro, D.C., Brook, A.H., Hughes, T.E., Sampson, W.J. & Townsend, G.C., Intrauterine hormone effects on tooth dimensions. Journal of Dental Research, 92, pp. 425–431, 2013. http://dx.doi.org/10.1177/0022034513484934
 Townsend, G., Bockmann, M., Hughes, T., Mihailidis, S., Seow, K.W. & Brook, A., New approaches to dental anthropology based on the study of twins (Chapter 2). New Directions in Dental Anthropology: Paradigms, Methodologies and Outcomes, eds. G. Townsend, E. Kanazawa & H. Takayama, University of Adelaide Press: South Australia, pp. 10–21, 2012.
 Hughes, T.E., Townsend, G.C., Pinkerton, S.K., Bockmann, M.R., Seow, W.K., Brook, A.H., Richards, L.C., Mihailidis, S., Ranjitkar, S. & Lekkas, D., The teeth and faces of twins: providing insights into dentofacial development and oral health for practicing oral health professionals. Australian Dental Journal, 59S, pp. 101–116, 2014. http://dx.doi.org/10.1111/adj.12101
 Brook, A.H., Smith, R.N., Elcock, C., al-Sharood, M.H., Shah, A.A., Khalaf, F., Robinson, D.L., Lath, D.L. & Karmo, M., The measurement of tooth morphology: validation of an image analysis system. 13th International Symposium of Dental Morphology. ed. E. Zadzinska, University of Lodz Press: Lodz, pp. 475–482, 2005.
 Schneider, C.A., Rasband, W.S. & Eliceiri, K.W., NIH Image to ImageJ: 25 years of image analysis. Nature Methods, 9, pp. 671–675, 2012. http://dx.doi.org/10.1038/nmeth.2089
 Gutiérrez-Redomero, E., Alonso, C., Romero, E. & Galera, V., Variability of fingerprint ridge density in a sample of Spanish Caucasians and its application to sex determination. Forensic Science International, 180, pp. 17–22, 2008.
 Griffin, J.E. & Wilson, J.D., Disorders of the testes and the male reproductive tract ( Chapter 18). Williams Textbook of Endocrinology, 10th edn., eds. P.R. Larsen, H.M. Kronemberg, S. Melmed & K.S. Polonsky, W.B. Saunders Company: Philadelphia, pp. 709–770, 2003.
 Reyes, F.I., Boroditsky, R.S., Winter, J.S.D. & Fairman, C., Studies on human sexual development. II. Fetal and maternal serum gonadotropin and sex steroid concentrations. Journal of Clinical Endocrinology and Metabolism, 38, pp. 612–617, 1974. http://dx.doi.org/10.1210/jcem-38-4-612
 Knickmeyer, R.C. & Baron-Cohen, S., Fetal testosterone and sex differences. Early Human Development, 82, pp. 755–760, 2006. http://dx.doi.org/10.1016/j.earlhumdev.2006.09.014
 AlQahtani, S.J., Hector, M.P. & Liversidge, H.M., Brief communication: the London atlas of human tooth development and eruption. American Journal of Physical Anthropology, 142, pp. 481–490, 2010. http://dx.doi.org/10.1002/ajpa.21258