How we value animals: the psychology of speciesism

In this thesis, consisting of three empirical projects (18 studies, total N = 8,218), I investigate how people morally value animals and why they value them less than humans. My central hypothesis is that people primarily value animals less than humans because of their mere species-membership, i.e. due to speciesism. First, I develop and validate a Speciesism Scale, a psychological assessment instrument that measures the extent to which people value humans more than animals. I find that speciesism is a stable construct with large interpersonal differences. It shares psychological properties with other forms of prejudice and predicts behaviour directed towards animals. Second, I experimentally investigate in more detail why people endorse speciesism. I develop a multi-factorial framework according to which people: a) believe that individuals should prioritise members of their owns species over others (Species-Relativism); b) have a slight tendency to consider humans to be of superior value in an absolute sense (Pro-Human Bias); and c) have a specific bias against animals (Anti-Animal Bias). I also show that people value animals less, the lower their perceived mental capacity levels are (Individual Mental Capacity View)—a principle that people selectively apply to animals but not to humans. Third, I experimentally investigate when people consider it permissible to harm animals or humans in cases where harming a few could save many. My findings support a model which I call Multi-level Weighted Deontology: deontological protections against harm are not absolute and get weaker the less people value the respective being, but they do not completely disappear. They are strongest for humans, followed by dogs, chimpanzees, pigs, and finally inanimate objects. Overall, my research shows that speciesism is a pervasive psychological phenomenon that strongly impacts our social lives and moral thinking. This thesis is one of the first attempts to transition speciesism from moral philosophy into psychology.