Human speech conveys emotions not only by words, but also by nonverbal acoustic cues. The hypothesis was tested that anger and joy can be conveyed in speech by displaying effort to sound larger or smaller, just as expressing dominance and submission in animal communication. Human listeners perceived vowels synthesized with a statically lengthened vocal tract and lowered pitch as from a large person, but from an angry person when the lengthening and lowering were dynamic. The opposite was true for perceiving small body size and joy. These results point to a size code shared by human and nonhuman communications.