Page 174 - Demo

Chapter 7172a study in rhesus macaques showed that females prefer to look longer at a more masculine male face in a pair of two (Rosenfield et al., 2019). In humans (PentonVoak & Chen, 2004; Pound et al., 2009), and potentially also in rhesus macaques (Rhodes et al., 1997), facial masculinity is linked to testosterone levels. This is also seems to be the case for orang-utan flanges: males with higher testosterone levels developed flanges earlier than individuals with lower testosterone levels (Emery Thompson et al., 2012). Altogether, our study is the first to describe a voluntary attentional bias towards a masculine trait in a great ape species, suggesting that a preference for masculine traits that are under the control of testosterone is shared across different primate species. Furthermore, we show that this preference appears to be expressed at both early stages of visual processing as well as at later stages that involve volitional control. One important caveat of our study is that we could not determine why orangutans were more attentive to flanged males. They may have had more interest in flanged males because they are potential mating partners. Alternatively, their vigilance towards flanged males could be due to the potential threat they pose to infants due to infanticide risk (Beaudrot et al., 2009; Knott et al., 2019). Importantly, we also found a bias towards flanged males in the one male that participated in our study, suggesting that male competition could also cause an attentional bias towards flanged males. Future studies could focus more on this specific aspect using methods such as priming or testing at different points during the menstrual cycle of a fully cycling female orang-utan. If an attentional bias towards flanged males is driven by a willingness to mate with them by female orang-utans, we would expect to see a stronger bias during ovulation. This would be in line with previous research suggesting that females actively approach flanged males to mate with them during ovulation (Knott et al., 2009), thus showing concordance between cognition and behaviour.However, very few studies have investigated ovulatory shift effects in nonhuman primates from a cognitive perspective, as such studies are difficult to conduct. In general, female primates in zoos and sanctuaries do not always have an active menstrual cycle as they are on birth control or have a dependent infant. To our knowledge, only one study has investigated the ovulatory shift effects in cognition in a non-human primate; Lacreuse et al. (2007)found evidence for increased attention towards, but not enhanced recognition of, male faces over female faces during the periovulatory period of rhesus macaques. Furthermore, recent studies in humans have also cast doubt on previously reported ovulatory Tom Roth.indd 172 08-01-2024 10:42