Scholarly estimates of the pre-Columbian population of Northern America have differed by millions of individuals: the lowest credible approximations propose that some 900,000 people lived north of the Rio Grande in 1492, and the highest posit some 18,000,000. In 1910 anthropologist James Mooney undertook the first thorough investigation of the problem. He estimated the precontact population density of each culture area based on historical accounts and carrying capacity, an estimate of the number of people who could be supported by a given form of subsistence. Mooney concluded that approximately 1,115,000 individuals lived in Northern America at the time of Columbian landfall. In 1934 A.L. Kroeber reanalyzed Mooney’s work and estimated 900,000 individuals for the same region and period. In 1966 ethnohistorian Henry Dobyns estimated that there were between 9,800,000 and 12,200,000 people north of the Rio Grande before contact; in 1983 he revised that number upward to 18,000,000 people.