Genes code for the expression of phenotypic traits, such as behavioral (e.g., aggressiveness) and morphological (e.g., opposing thumbs) traits. Costly traits are phenotypic traits that evolved in spite of imposing a fitness cost, often in the form of a survival handicap. In non-human animals, the classic example of costly trait is the peacock's train, used by males to signal good health to females. It is argued here that oral speech is a costly trait evolved by our human ancestors to enable effective knowledge communication. It is shown that, because it is a costly trait, oral speech should be a particularly strong determinant of knowledge communication performance; an effect that generally applies to e-collaborative tasks performed by modern humans. The effects of oral speech support in e-collaborative tasks are discussed based on empirical studies, and shown to be consistent with the notion that oral speech is a costly trait. Specifically, it is shown that the use of e-collaboration technologies that suppress the ability to employ oral speech, when knowledge communication is attempted, leads to the two following negative outcomes: (a) a dramatic decrease in communication fluency, and (b) a significant increase in communication ambiguity. These effects are particularly acute in e-collaborative tasks of short duration.