Personality and Individual Diferences 172 (2021) 110575 0191-8869/© 2020 Elsevier Ltd. All rights reserved. Short Communication Digit ratio (2D:4D) a possible biomarker for cognitive style: A study on Iranian engineering and mathematics university students Armin Rajab a , Milad Shafzadeh b , Manouchehr Nakhjavani a , Abdol-Hossein Vahabie c, d, e , Mahdiyeh Salehi f , Sahar Zarei g , Amirhossein Memari h , Fatemeh Sadat Mirfazeli i, * a Endocrinology and Metabolism Research Center (EMRC), Vali-Asr Hospital, Tehran University of Medical Sciences, Tehran, Iran b Department of Neurosurgery, Tehran University of Medical Sciences, Iran c Cognitive Systems Laboratory, Control and Intelligent Processing Center of Excellence (CIPCE), School of Electrical and Computer Engineering, College of Engineering, University of Tehran, Tehran, Iran d Department of Psychology, Faculty of Psychology and Education, University of Tehran, Tehran, Iran e School of Cognitive Sciences, Institute for Research in Fundamental Sciences, Tehran, Iran f School of Behavioral Sciences and Mental Health (Tehran Institute of Psychiatry), Iran University of Medical Sciences, Iran g Department of Cognition and Communication, University of Copenhagen, Denmark h Sport Medicine Research Center, Neuroscience Institute, Tehran University of Medical Sciences, Iran i Mental Health Research Center, School of Behavioral Sciences and Mental Health (Tehran University of Psychiatry), Iran University of Medical Sciences, Iran A R T I C L E INFO Keywords: Digit ratio Systemizing and empathizing Reading the mind in the eyes test (RMET) Gender difference ABSTRACT Digit ratio (2D:4D) is a biomarker for prenatal hormonal exposure. Some studies suggest that prenatal hormonal exposure might infuence our cognitive styles characterized by systemizing and empathizing tendencies while other studies do not support these fndings. By assessing 156 university students of engineering or mathematics (science, technology, engineering, and mathematics (STEM) (female: 63 and male 93) we concluded that digit ratio may support the hypothesis on sexual differences in cognitive styles. 1. Introduction Digit Ratio is calculated by dividing the second digit (2D, index fnger) length by the fourth digit (4D, ring fnger) length of the same hand. A great deal of research has shown that digit ratio (2D:4D) cor- relates with the prenatal testosterone exposure, and it seems that lower digit ratio can be supposed as a proxy for a higher concentration of testosterone in fetal development (Cohen-Bendahan et al., 2005; Manning, 2011; Zheng & Cohn, 2011). Besides, early studies have re- ported that digit ratio varies by gender and ethnicity; however, the male’s digit ratio tends to be smaller than the female’s digit ratio in all ethnic groups and this difference is more obvious in the right hand (Manning, 2011). Recently it has been suggested that digit ratio also correlates with cognitive styles characterized by systemizing and empathizing tendency (Manning et al., 2010; Van Honk et al., 2011). Based on systemizing and empathizing (E-S) theory, systemizers tend towards exploring rules of a rule-based system while empathizers tend to understand others’ beliefs, thoughts, emotions, actions and to respond to them accordingly (Goldenfeld et al., 2005). Previously it was suggested that digit ratio inversely correlates with a higher systemizing tendency (Manning et al., 2010); however, Voracek et al. in their study found that digit ratio was unrelated to systemizing and empathizing cognitive style among a sample of Austrian general population (Voracek & Dressler, 2006). Hence this matter is yet controversial. Therefore, in this study, we aimed to investigate the relationship between digit ratio and cognitive style among students of mathematics (Kidron et al., 2018) and engineering who are known for having higher systemizing brain (Focquaert et al., 2007) in Iranian population. 2. Method A total number of 156 engineering or mathematics (science, tech- nology, engineering, and mathematics (STEM)) students (aged = 18–29, mean = 22.3, SD = 2.4, 63 women) from three different universities in Tehran have been recruited. Subjects were asked to complete the short forms of both 25-statement systemizing quotient questionnaire (SQ) and * Corresponding author at: Social Neuroscience Neurocognition Division of Mental Health Research Center, Iran University of Medical Sciences, Niayesh St, Hazrate Rasoole Akram Hospital, Tehran, Iran. E-mail addresses: nakhjavanim@tums.ac.ir (M. Nakhjavani), h.vahabie@ut.ac.ir (A.-H. Vahabie), mirfazeli.f@iums.ac.ir (F.S. Mirfazeli). Contents lists available at ScienceDirect Personality and Individual Differences journal homepage: www.elsevier.com/locate/paid https://doi.org/10.1016/j.paid.2020.110575 Received 9 October 2020; Received in revised form 27 November 2020; Accepted 29 November 2020