Darwin's theory predicts that linguistic behavior gradually evolved out of animal forms of communication (signaling). However, this prediction is confronted by the conceptual problem that there is an essential difference between signaling and linguistic behavior: using words is a normative practice. It is argued that we can resolve this problem if we (1) note that language evolution is the outcome of an evolutionary transition, and (2) observe that the use of words evolves during ontogenesis out of babbling. It is discussed that language evolved as the result of an expansion of the vocalizing powers of our ancestors. This involved an increase in the volitional control of our speech apparatus (leading to the ability to produce new combinations of vowels and consonants), but also the evolution of socially guided learning. It resulted in unique human abilities, namely doing things with words and later reasoning and giving reasons.