The COVID-19 pandemic has brought science into the public eye and to the attention of governments more than ever before. Much of this attention is on work in epidemiology, virology, and public health, with most behavioural advice in public health focussing squarely on ‘proximate’ determinants of behaviour. While epidemiological models are powerful tools to predict the spread of disease when human behaviour is stable, most do not incorporate behavioural change. The evolutionary basis of our preferences and the cultural evolutionary dynamics of our beliefs drive behavioural change, so understanding these evolutionary processes can help inform individual and government decision-making in the face of a pandemic.

Male homosexual preference (MHP) is an evolutionary enigma because it is partially heritable and imposes a fertility cost. In occidental societies, homosexual men are feminized at various levels and they have more older brothers than heterosexual men. To evaluate whether femininity and the fraternal birth order (FBO) effect are universal features of MHP or not, we collected original data from homosexual men, heterosexual men, and heterosexual women from Java (Indonesia). Facial photographs were used to test whether homosexual faces are feminized when compared with heterosexual ones. We found that faces manipulated to resemble the average face of homosexual men are perceived as facially feminized, suggesting that homosexual men are facially feminized compared to heterosexual men, although a higher facial femininity was not captured by morphological analyses. Then, family data were used to detect differences in siblings’ composition between homosexuals and heterosexuals. Homosexual men displayed a higher number of older brothers than heterosexual men, even when sibship size was controlled for, suggesting that the FBO effect exists in Indonesian populations. Independent of sexual orientation, men with older brothers seem more feminized than those without older brothers, consistent with the immune origin of the FBO effect. In conclusion, MHP in Indonesia is partially feminized and they have more older brothers. Such features are also associated with MHP in other cultural contexts, suggesting a cross-cultural effect of men homosexual preference. An evolutionary explanation is available for the feminizing effect, although the FBO effect remains unexplained even if proximal mechanisms start to be identified.

The genus Macaca, member of sub-family Cercopithecinae, is the most widely distributed non-human primates in Asian countries. The habitats are strongly influence the dietary variation of the populations. The dietary variation of the macaques reflect ecological plasticity in coping with differences both in availability and abundance of food. The macaques are plastic in taking any kind of food that available in their home range and adjust their behaviour according to its abundance. Here, we present the dietary variation of long-tailed macaques (Macaca fascicularis) in the high altitude rain forest of Telaga Warna, West Java, Indonesia. The proportion of their food from natural sources is greater than those from visitors. The natural food consisted of plants, small animals (insects and earthworm), fungi and water from lake. The plant food comprised of 29 species plus a few mosses. The frequency of eating artificial food was influenced by visitors who come for picnic. In this site, the macaques learned that the visiting of tourists is identical with food.

Tsuji et al. 2 2We observed an inter-species association between wild Javan lutungs (Trachypithecus auratus) and rusa deer (Rusa timorensis). In this association, the former drops plant items that the latter subsequently consumes (glean). We investigated whether the association is beneficial for deer that inhabit tropical regions characterized by drastic seasonal changes. Between 2011 and 2013, we conducted field surveys in the Pangandaran Nature Reserve, Indonesia. We observed 248 gleaning events; the total duration (60.1 h) of these gleaning events corresponded to approximately 4% of the lutung observation time. Deer consumed 39 items dropped by lutungs; these items belonged to 28 plant species and included leaves, fruits, and flowers. Gleaning events occurred more frequently during months when rainfall was low and few herbaceous plants grew in grassland patches. Gleaned foods were significantly heavier than non-gleaned foods. Our findings imply that the lutung-deer association is beneficial to deer, by improving nutritional condition during seasons with low food resources.

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