Dispersal does not only mean moving from one environment to another, but can also refer to shifting from one social group to another. Individual characteristics such as sex, age and family structure might influence an individual's propensity to disperse. In this study, we use a unique dataset of an evacuated World War II Finnish population, to test how sex, age, number of siblings and birth order influence an individual's dispersal away from their own social group at a time when society was rapidly changing. We found that young women dispersed more than young men, but the difference decreased with age. This suggests that young men might benefit more from staying near a familiar social group, whereas young women could benefit more from moving elsewhere to find work or spouses. We also found that having more younger brothers increased the propensity for firstborns to disperse more than for laterborns, indicating that younger brothers might pressure firstborn individuals into leaving. However, sisters did not have the same effect as brothers. Overall, the results show that individual characteristics are important in understanding dispersal behaviour, but environmental properties such as social structure and the period of flux after World War II might upend the standard predictions concerning residence and dispersal.

Social media summary: Individual characteristics influence dispersal away from social group after a forced migration in a Finnish population

The goal of this study was to demonstrate the role of isolation on the social behaviour of individuals and to characterize its adaptation as a function of time. The ethological method used was a quantitative description of the spatial positioning of a sub-group of 13 wintering members during the morning, midday and evening meals at Dumont d'Urville station. The observation protocol required the completion of first daily and then weekly (every Thursday) observation maps at different stages of the 13 month long polar mission, from the information seminar in France, the trips outward and return aboard the Astrolabe, the two summer campaigns at the beginning and at the end of the mission and the overwintering period. Results, mainly expressed as human concentration and spatial dispersion indexes, have successively shown organization, disorganization and reorganization periods of the small group without any significant cycling. Socialisation rules promoting the group building in the early period, conflict factors and relay steps (external perturbations breaking the isolation, transitions during group displacement from one stage to another) promoting the maintenance of the social cohesion, are outlined in the discussion.

Dietary records were obtained twice in pregnancy and once post-partum, from 265 women in all social classes in London and Edinburgh. Some Edinburgh women, and lactating women, showed the higher levels of calcium intake. For iron, retinol, ascorbic acid and folic acid, there was a consistent and significant regional and social class gradient in intakes. This favoured English women in ‘non-manual’ social groups, leaving the Scottish ‘manual’ class, after pregnancy, with the lowest intakes. Mean intakes of Ca and Fe were consistently below the current UK recommended daily amount (RDA). Intakes of retinol were all above it, and ascorbic acid intakes ranged above and below the RDA.