It's what on the inside that counts: Addressing the biodiversity crisis by emphasizing species' inner mental lives

The biodiversity crisis is threatening the survival of many species on our planet. This is exacerbated by the taxonomic bias, with species taxonomically closer to humans receiving most funding and attention. The current research explores species engagement – our sense of connection to and concern for other species – through a social similarity approach. We distinguish between two factors influencing perceptions, attitudes and behavior regarding other animals: bottom-up visual cues (physical similarity) and top-down beliefs about animals’ capacities (mental similarity). Combining a correlational (Studies 1: N = 33 and 2: N = 564) and an experimental approach (Study 3: N = 330), we investigated the relative importance of these two factors for species engagement – operationalized as self-other overlap, moral concern, and conservation support. Study 1 and 2 reveal that mental similarity has up to five times the impact of physical similarity on perceived overlap, moral concern, and conservation support. Study 3 broadly replicates these findings, with both mental and physical similarity affecting perceived overlap and moral concern. However, only physical similarity was found to affect conservation support. Potential explanations are discussed. Findings demonstrate the usefulness of a social similarity approach to conservation psychology and offer a novel perspective for communications around nature conservation. • The more a species looks like us, the more we engage with them. • Regardless of appearance, mental similarity also induces species engagement. • Emphasizing inner mental lives of species can mitigate taxonomic bias. • Social similarity framework aids understanding of conservation psychology. • Future conservation efforts should highlight species' mental capacities.