  Humans possess the unique ability to communicate emotions through language.
Although concepts like anger or awe are abstract, there is a shared consensus
about what these English emotion words mean. This consensus may give the
impression that their meaning is static, but we propose this is not the case.
We cannot travel back to earlier periods to study emotion concepts directly,
but we can examine text corpora, which have partially preserved the meaning of
emotion words. Using natural language processing of historical text, we found
evidence for semantic change in emotion words over the past century and that
varying rates of change were predicted in part by an emotion concept's
prototypicality - how representative it is of the broader category of
"emotion". Prototypicality negatively correlated with historical rates of
emotion semantic change obtained from text-based word embeddings, beyond more
established variables including usage frequency in English and a second
comparison language, French. This effect for prototypicality did not
consistently extend to the semantic category of birds, suggesting its relevance
for predicting semantic change may be category-dependent. Our results suggest
emotion semantics are evolving over time, with prototypical emotion words
remaining semantically stable, while other emotion words evolve more freely.
