and three books. He has also edited or co-edited four books. Maori Warfare, the book based on Vayda's Ph.D. dissertation, was first published in 1960. Now a classic, it has been regarded as the authoritative work on the subject of Maori warfare in its last stage of evolution before being greatly altered by European weapons and ways. As such, it continues to guide archaeological research in New Zealand and has been important also for anthropological and ecological studies of war. In the 1960s, Vayda extended his studies of intergroup fighting to societies in Borneo and New Guinea. His New Guinea findings have special value as products of field research carried out among groups contacted and pacified by outsiders only a few years earlier. The findings figure prominently in an important 1989 article, “Explaining Why Marings Fought.” In this, Vayda admitted to certain errors of reification and fallacies of functional explanation in some of his own earlier work and he showed how avoidable ambiguities in the meaning of questions about why people fight have led to long, unproductive, and acrimonious debates among scholars. This last theme was taken up again in a 1992 review article on the anthropology of war. Both articles are included in Vayda's 2009 essay collection, Explaining Human Actions and Environmental Changes. The 1989 article is noteworthy also as an extended illustration of Vayda's abiding interest in analyzing and explaining explanation itself and in engaging with the philosophical literature on explanation. Vayda's year (1956–57) in the coral atolls of the Northern Cook Islands failed to produce the ethnographic monograph expected at the time from extended anthropological fieldwork. However, it did result in a number of articles, including some on such unconventional topics as the relation of island size to sexual activity and to openness to cultural innovations. Throughout his career, Vayda's efforts have been directed mainly towards the production of critical, analytic articles on various topics rather than big books with overarching themes. Having become involved in UNESCO's Man and Biosphere Program, Vayda directed or co-directed in the 1970s and 1980s a series of interdisciplinary projects on the causes of deforestation in the Indonesian province of East Kalimantan on the island of Borneo. The projects resulted in useful data on how, why, and to what extent did specific activities such as legal and illegal logging, pepper farming by migrants from another island, and shifting cultivation, contribute to deforestation.