There is a correlation between the phonological shape of a word and the word’s probability in use. Less probable words tend to be longer and more probable words shorter (see Piantadosi et al. , Zipf ). This has been attributed to the lexicon evolving for efficient communication (Zipf ). To identify less probable words, listeners need more information from the segments in the phonological word itself. In this case, longer lengths for less probable words mean a greater amount of information to be used in word identification. However, this does not take into account how listeners actually process words. Research in spoken word recognition has shown that words are processed incrementally and some segments may in fact be more informative (Allopenna et al. , Luce and Pisoni , van Son and Pols , Weber and Scharenborg ). Here, we use corpus data from American English to provide evidence that less probable words contain more informative segments. We also show that the distribution of segmental information is correlated with the word’s probability and that less probable words contain more of their total information in the early segments. We discuss these findings and possible evolutionary avenues for language to reach this state. This work provides support for the idea that the words in the lexicon evolve under pressure for efficient communication.

The past few years have led to the widespread recognition that morphology is an independent domain of language functioning in dynamic interdependence with more familiar domains such as phonology and syntax. This has permitted nuanced research into the organization of morphological systems as well as the development of hypotheses concerning factors responsible for such organization. In this chapter we compare two classes of hypotheses — adaptive explanations and neutral ones — for attested differences in morphological complexity claimed to correspond with sociocultural and demographic factors. While both examine language change as a (cultural) evolutionary process, we argue that much recent work on adaptive hypotheses for morphological complexity has been uncritically adaptationist, neglecting key results and lessons from population genetics about how to study evolutionary systems. Finally, we argue that neutral explanations are presently more likely explanations for the apparent association of morphological complexity and smaller, historically more isolated populations and should a priori be preferred over adaptive explanations unless and until a high evidential burden has been met.