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.

The influence of inclusive fitness interests on the evolution of human institutions remains unclear. Religious celibacy constitutes an especially puzzling institution, often deemed maladaptive. Here, we present sociodemographic data from an agropastoralist Buddhist population in western China, where parents sometimes sent a son to the monastery. We find that men with a monk brother father more children, and grandparents with a monk son have more grandchildren, suggesting that the practice is adaptive. We develop a model of celibacy to elucidate the inclusive fitness costs and benefits associated with this behaviour. We show that a minority of sons being celibate can be favoured if this increases their brothers' reproductive success, but only if the decision is under parental, rather than individual, control. These conditions apply to monks in our study site. Inclusive fitness considerations appear to play a key role in shaping parental preferences to adopt this cultural practice.

An accurate reconstruction of Sino-Tibetan language evolution would greatly advance our understanding of East Asian population history. Two recent phylogenetic studies attempted to do so but several of their conclusions are different from each other. Here we reconstruct the phylogeny of the Sino-Tibetan language family, using Bayesian computational methods applied to a larger and linguistically more diverse sample. Our results confirm previous work in finding that the ancestral Sino-Tibetans first split into Sinitic and Tibeto-Burman clades, and support the existence of key internal relationships. But we find that the initial divergence of this group occurred earlier than previously suggested, at approximately 8000 years before the present, coinciding with the onset of millet-based agriculture and significant environmental changes in the Yellow River region. Our findings illustrate that key aspects of phylogenetic history can be replicated in this complex language family, and calls for a more nuanced understanding of the first Sino-Tibetan speakers in relation to the “early farming dispersal” theory of language evolution.

Abstract

Beliefs about the fate of humanity and the soul after death may structure behaviours of religious groups. Here we test theories from religious studies: that beliefs of an imminent apocalypse co-evolved with and facilitated revolutionary violence, while reincarnation beliefs cause people to acquiesce to existing social orders and withdraw from political activism. We test these hypotheses by building a cultural phylogeny of historical Islamic sects and schools from the 7-20 th centuries and use phylogenetic comparative methods to show that these two beliefs display distinct relationships with intergroup violence. There is substantial evidence that apocalyptic beliefs co-evolved with revolutionary violence, while reincarnation beliefs were evolutionarily stable in peaceful groups. In both cases, violence precedes the emergence of beliefs, which suggests that conditions which generate revolutionary violence changed beliefs rather than beliefs generated violence. We also found that apocalyptic beliefs are associated with accelerated group extinction, although causal relationships cannot be determined.