Mere presence of co-eater automatically shifts foraging tactics toward “fast and easy” food in humans

Competition for food resources is widespread in nature. The foraging behavior of social animals should thus be adapted to potential food competition. We hypothesized that in the presence of co-foragers, animals would shift their tactics to forage more frequently for smaller food. Because smaller foods are more abundant in nature and allow faster consumption, such tactics should allow animals to consume food more securely against scrounging. We tested whether humans would exhibit such a shift. To prevent subjects from having rivalry, they were instructed to engage in a “taste test” in a laboratory, alone or in pairs. Even though the other subject was merely present and there was no real competition for food, subjects in pairs immediately exhibited a systematic behavioral shift to reaching for smaller food amounts more frequently, which was clearly distinct from their reaching patterns both when eating alone and when simply weighing the same food without eating any. These patterns suggest...