Contents lists available at ScienceDirect Personality and Individual Differences journal homepage: www.elsevier.com/locate/paid Understanding the Simber Effect: Why is the age-dependent increase in children's cognitive ability smaller in Arab countries than in Britain? Salaheldin Farah Attallah Bakhiet a,⁎ , Edward Dutton b , Khalil Yousif Ali Ashaer c , Yossry Ahmed Sayed Essa a , Tahani Abdulrahman Muhammad Blahmar a , Sultan Mohammed Hakami a , Guy Madison d a Department of Special Education, King Saud University, Saudi Arabia b Ulster Institute for Social Research, London, United Kingdom c Department of Special Education, Najran University, Saudi Arabia d Umeå University, Umeå, Sweden ARTICLE INFO Keywords: Flynn effect Life history theory Arabic IQ Intelligence ABSTRACT Previous research indicates that the typical increase in IQ during childhood is greater in European countries than in Arab countries. A systematic literature review of age-dependent IQ in Arab countries is conducted, yielding relevant studies for 12 countries that fulfil the inclusion criteria. In almost all of these studies, Arab children exhibit an age-dependent IQ decline relative to Caucasian children, from 5 to about 12 years of age in particular. We term this phenomenon the Simber Effect. We propose two non-exclusive explanations. (1) The Flynn Effect is less intense in Arab countries because of localised differences, including poorer education quality and greater religiosity. (2) Those from Arab countries follow a faster Life History Strategy than Europeans, for environmental and possibly genetic reasons. Either way, the Simber Effect may amount to a Wilson Effect, meaning that the impact of genetic IQ increases with age. 1. Introduction Many studies have examined intelligence in Arab countries in comparison to that of Western countries. Lynn (2015) has compiled assorted administrations of various intelligence tests in the Arab world and compared them to British norms to achieve ‘Greenwich IQs’ for each country. Estimations of the average Greenwich IQ of Arab coun- tries are mainly between 80 and 85. As with Western countries, the Flynn Effect – the secular increase in IQ scores across the twentieth century – have been found in some Arab countries, specifically in Saudi Arabia and Sudan (see Batterjee, Khaleefa, Ali, & Lynn, 2013; Flynn, 2012). ‘Negative Flynn Effects’– secular declines in IQ scores – have been reported in Khartoum (Dutton, Bakhiet, Ziada, Essa, & Blahmar, 2017) as well as in Kuwait (Dutton, Bakhiet, Essa, Blahmar, & Hakami, 2017), although these authors have argued that, unlike with Western Negative Flynn Effects (see Dutton, Van der Linden, & Lynn, 2016), these appear to have mainly environmental rather than partly genetic causes. Although the average IQ of Arab countries would – for whatever reason – appear to be around one standard deviation lower than the Greenwich norm, there is an aspect to this difference to which little attention has been paid and which has not previously been clearly presented. Put simply, there is evidence of age variation in the extent of the difference: age-dependent cognitive decline. The IQs of child sam- ples in Arab countries are lower than the Greenwich IQ, but this dif- ference increases as the children age. We term this phenomenon the Simber Effect, after the Sudanese black stork whose appearance heralds the start of the rainy season and the growth of the crops. After his appearance and the arrival of the rains, the land is highly productive, but this only lasts for a brief period. Here, we attempt to describe this phenomenon exhaustively by conducting a systematic literature review, and by contrasting the results with samples from European countries. Possible explanations for the Simber Effect are sought in cultural and environmental factors and in evolutionary theory, specifically Life History theory and gene-en- vironment interaction. 2. Method This study involves a secondary analysis of all known English-lan- guage studies of IQ in Arab countries, calculated against Greenwich norms. In order to find these, we conducted a systematic literature http://dx.doi.org/10.1016/j.paid.2017.10.002 Received 1 August 2017; Received in revised form 30 September 2017; Accepted 3 October 2017 ⁎ Corresponding author. E-mail addresses: slh9999@yahoo.com (S.F.A. Bakhiet), ysayed@ksu.edu.sa (Y.A.S. Essa), tbalahmar@ksu.edu.sa (T.A.M. Blahmar), guy.madison@umu.se (G. Madison). Personality and Individual Differences 122 (2018) 38–42 0191-8869/ Crown Copyright © 2017 Published by Elsevier Ltd. All rights reserved. MARK