The article shows that during the forming of grammatical category of gender in Indo-European languages, names of non-living objects and names of those animals whose sex is unimportant for humans were receiving grammatical meanings of gender on the basis of similarity or dissimilarity of designated objects with males or females. Such grammatical metaphors were based on the ideas of different peoples about some minor characteristics of persons of different sex, such as the difference between men and women with higher activity, greater size, strength and independence. By now, the metaphorical motivation of category of gender in the Russian language has survived only in certain nouns. These nouns are interrogative pronouns кто (masc.) ʻwhoʼ and что (neut.) ʻwhatʼ, paired nouns-synonyms, e. g. конь (masc.) ʻstrong horseʼ – лошадь (fem.) ʻordinary horseʼ, generic versions of nouns, e. g. ворон (masc.) ʻravenʼ – ворона (fem.) ʻcrowʼ, and nouns-occasionalisms used in speech oriented to expressiveness and creativity.