met·a·phor
noun
a figure of speech in which a word or phrase is applied to an object or action to which it is not literally applicable.
That's the definition I had in mind. I agree hunger and thirst are not metaphors.
I didn't intend to make an argument that they were. I do not think that 'reproductive impusle' fits into the same category.
Hunger and thirst are experienced phenotypically and satisfying them promotes the survival of the individual.
Sexual arousal and its satisfaction via orgasm promotes the happiness and well being of the individual , but is not a survival drive in the same sense.
Dehydration and under nourishment will lead to death of the individual, but a frustrated sexual urge is not fatal.
Lumping them together is a form of metaphor or a mischaracterization.