Humans favor and venerate their ingroups, while disregarding outgroups to the degree of dehumanizing them. We explore the social construction of such boundaries and its associated speciesism toward two nonhuman outgroups: animals and machines. For this, we analyzed UK newspaper coverages of the binaries Human–Animal and Human–Machine between 1995 and 2010. We quantified if and how tolerance toward ambiguous concepts that challenge and expand definitions of humanness (e.g., nonhuman primates, cyborgs) varied across time as well as with journalist gender, political leaning, and expertise. In this analysis, the ca. 1100 individual journalists stood as proxies for the British public and therefore as a human-ingroup subset. We found more tolerance toward intermediaries in broadsheet newspapers, females, and subject experts, as opposed to tabloids, males, and subject novices. Moreover, ambiguity tolerance hit a low during the year 2000, likely due to Western sociopolitical turbulence—potentially including wider societal stress over the landmark millennium year itself—attesting that ingroups become more closed during stressful times. Compared with the plasticity of the Human–Animal dichotomy, the Human–Machine binary was more rigid, indicating that the relative novelty of IT developments triggers increased caution and anxiety. Our research suggests that cognitive mechanisms facilitating human-ingroup protection are deep-rooted, albeit malleable according to changing socioeconomic conditions
