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Absence of cognitive bias to flanges in orang-utans1296IntroductionPrimates have a highly specialized visual system (Barton, 1998; DeCasien & Higham, 2019), and the importance of visual signalling becomes especially apparent in group living species. For example, primates attend to faces of conspecifics (Kano et al., 2012) and discriminate faces based on different characteristics, such as emotional expressions (Pritsch et al., 2017) and familiarity (Leinwand et al., 2022; Lewis, 2017; van Berlo et al., 2023). Importantly, primate faces can also signal cues that are relevant for mate choice, such as health or dominance (Petersen & Higham, 2020). Consequently, primates might have cognitive biases related to sexually relevant facial characteristics. Examples of such traits are sexually dimorphic characteristics and facial symmetry (Little, Jones, et al., 2011; Rhodes, 2006). However, previous work on this topic has mostly focused on rhesus macaques, and very few studies have studied cognitive biases to sexually relevant facial characteristics in great apes. Therefore, the present paper aims to investigate whether Bornean orang-utans (Pongo pygmaeus) have cognitive biases for such facial characteristics using an immediate attention task and a preference task.Cognitive processes are strongly influenced by evolutionarily relevant contexts, such as mate choice (Kenrick et al., 2010; Schaller et al., 2017). Mate choice is one of the most important aspects of an animal’s life: choosing a suitable mate might ensure a good representation of the individual’s genes in the next generation. Because of this strong incentive to choose a suitable mate, many species have evolved specific mate preferences that guide individuals during the mate choice process (Darwin, 1871; Manson, 2011). For humans, it has been established that preferences affect social cognition: several cognitive processes, such as attention (e.g., Roth et al., 2022, 2023), memory (e.g., Lin et al., 2020), and effort (e.g., Levy et al., 2008), are modulated by physical attractiveness. For non-human primates, research on this topic is still relatively scarce. While previous work has mainly focused on looking preferences, and how these are modulated by sexual dimorphic traits (Dubuc et al., 2016; Rosenfield et al., 2019; Waitt et al., 2003), few studies have investigated other cognitive processes such as direct attention or choice bias (Watson et al., 2012). Furthermore, most of the aforementioned studies have focused on rhesus macaques (Macaca mulatta), even though a good understanding of the cognitive processes associated with sexual selection requires investigation of a wide range of species.Tom Roth.indd 129 08-01-2024 10:41