The Typological Prevalence Hypothesis1

F or me (Dedre) Dan has been a protean figure. 1 first met him when I was a graduate student at the University of California, San Diego and he was a young professor at Berkeley. He was brilliant, charismatic, and compelling, yet at times engagingly shy. We stayed connected through a circle of friends centered in Nijmegen and the Bay Area, a group united by a passion for psychoIogically juicy theories of language acquisition and for crosslinguistic approaches-both signature positions of Dan's throughout his career. This has led to a many shared quests, and, ultimately, to deep bonds of friendship and respect. Dan and I (Melissa) fledged in the same academic nest at Harvard and were influenced by many of the same mentors, prime among them Roger Brown, but also Bruner, Miller, and Lenneberg. But Dan was there just before me, and had already finished and gone to Berkeley the year I arrived. Although I met him when he came back for a visit, I did not really get acquainted until I participated in his course at the fanious 1968 U. C. Berkeley summer school, "Language, Society, and the Child." I remember worrying about how to address him-could 1 presume to call him "Dan"? Now after years of friendship this makes me laugh, because Dan was then only 29 years old! But such was already his influence and natural authority. Down the years, Dan and I saw each other often-in Berkeley (conveniently, my home town), at the Max Planck Institute, and at conferences around the world. Language acquisition, of course, was often the focus of our discussions and sometimes heated