Archaeological records of the fourth and third millennia B.P. in eastern New England, from Massachusetts to Maine, evidence the initiation and spread of intensive shellfish exploitation from a Late Archaic forest and riverine-oriented economic base. Changes in the degree of exploitation of several shellfish species follow the economic shift during Early and Middle Woodland times. Ritchie and Snow have recently explained these changes as the result of a single process of purely internally initiated cultural evolution involving a systematic expansion of exploitative techniques and the subsistence base. Evidence from the Boston Harbor area, Massachusetts, and from paleoclimatic, ecological, and paleoecological literature are presented in arguing that such an explanation is unwarranted. An alternative framework, emphasizing the primacy of ecological factors, is presented.