What is the theme in Cod: A Biography of the Fish That Changed the World by Mark Kurlansky?

Cod helped shape human history is a theme in the book. Part I of the book examines in considerable detail the interaction between humans and cod, nearly exclusively from the viewpoint that cod are an important food and have often been a significant commercial commodity. Several centuries ago, cod's ready availability as a desirable food item led to early commercial exploitation of cod fisheries. Early curing techniques typically used air drying of prepared fish and led to the establishment of various colonies or outposts. Later curing methods utilized salting and, with other foods, led to secondary commercial development of salt extraction. Various nationalities became ascendant in the cod trade as global markets developed or declined—the earliest dominant national force in the cod trade was focused in the Basque region of Spain; ironic, considering that Spain has never had a good local cod fishery.