Population ethical intuitions.

Is humanity's existence worthwhile? If so, where should the human species be headed in the future? In part, the answers to these questions require us to morally evaluate the (potential) human population in terms of its size and aggregate welfare. This assessment lies at the heart of population ethics. Our investigation across nine experiments (N = 5776) aimed to answer three questions about how people aggregate welfare across individuals: (1) Do they weigh happiness and suffering symmetrically?; (2) Do they focus more on the average or total welfare of a given population?; and (3) Do they account only for currently existing lives, or also lives that could yet exist? We found that, first, participants believed that more happy than unhappy people were needed in order for the whole population to be net positive (Studies 1a-c). Second, participants had a preference both for populations with greater total welfare and populations with greater average welfare (Study 3a-d). Their focus on average welfare even led them (remarkably) to judge it preferable to add new suffering people to an already miserable world, as long as this increased average welfare. But, when prompted to reflect, participants' preference for the population with the better total welfare became stronger. Third, participants did not consider the creation of new people as morally neutral. Instead, they viewed it as good to create new happy people and as bad to create new unhappy people (Studies 2a-b). Our findings have implications for moral psychology, philosophy and global priority setting.

Should you save the more useful? The effect of generality on moral judgments about rescue and indirect effects.

Across eight experiments (N = 2310), we studied whether people would prioritize rescuing individuals who may be thought to contribute more to society. We found that participants were generally dismissive of general rules that prioritize more socially beneficial individuals, such as doctors instead of unemployed people. By contrast, participants were more supportive of one-off decisions to save the life of a more socially beneficial individual, even when such cases were the same as those covered by the rule. This generality effect occurred robustly even when controlling for various factors. It occurred when the decision-maker was the same in both cases, when the pairs of people differing in the extent of their indirect social utility was varied, when the scenarios were varied, when the participant samples came from different countries, and when the general rule only covered cases that are exactly the same as the situation described in the one-off condition. The effect occurred even when the general rule was introduced via a concrete precedent case. Participants' tendency to be more supportive of the one-off proposal than the general rule was significantly reduced when they evaluated the two proposals jointly as opposed to separately. Finally, the effect also occurred in sacrificial moral dilemmas, a general phenomenon occurring in multiple moral contexts. We discuss possible explanations of the effect, including concerns about negative consequences of the rule and a deontological aversion against making difficult trade-off decisions unless they are absolutely necessary.

Impact of the Mk VI SkinSuit on skin microbiota of terrestrial volunteers and an International Space Station-bound astronaut.

Microgravity induces physiological deconditioning due to the absence of gravity loading, resulting in bone mineral density loss, atrophy of lower limb skeletal and postural muscles, and lengthening of the spine. SkinSuit is a lightweight compression suit designed to provide head-to-foot (axial) loading to counteract spinal elongation during spaceflight. As synthetic garments may impact negatively on the skin microbiome, we used 16S ribosomal RNA (rRNA) gene amplicon procedures to define bacterial skin communities at sebaceous and moist body sites of five healthy male volunteers undergoing SkinSuit evaluation. Each volunteer displayed a diverse, distinct bacterial population at each skin site. Short (8 h) periods of dry hyper-buoyancy flotation wearing either gym kit or SkinSuit elicited changes in the composition of the skin microbiota at the genus level but had little or no impact on community structure at the phylum level or the richness and diversity of the bacterial population. We also determined the composition of the skin microbiota of an astronaut during pre-flight training, during an 8-day visit to the International Space Station involving two 6-7 h periods of SkinSuit wear, and for 1 month after return. Changes in composition of bacterial skin communities at five body sites were strongly linked to changes in geographical location. A distinct ISS bacterial microbiota signature was found which reversed to a pre-flight profile on return. No changes in microbiome complexity or diversity were noted, with little evidence for colonisation by potentially pathogenic bacteria; we conclude that short periods of SkinSuit wear induce changes to the composition of the skin microbiota but these are unlikely to compromise the healthy skin microbiome.