Environmental ethicists trace the roots of modern American environmental attitudes to the idea of private ownership. During the European Middle Ages, a strong ideal of individual land ownership emerged, in contrast to control by a ruler or a governmental body. This became the basis of property rights in the American Colonies of Britain, as advocated by Thomas Jefferson. The strongly held belief of the right to hold private property remains a cornerstone of American thinking, and is often at odds with issues of environmental ethics.
Farming the land was not the only activity in the early history of the development of the North American continent by European settlers. Before there was significant development of farmland in the interior of the continent, explorers, trappers, and naturalists were looking over the landscape for other reasons. During the eighteenth and nineteenth centuries, the attitudes of naturalists and hunters about killing animals were similar. For the naturalist, it was the only way to examine new species up close. For the hunter, killing animals was a way of making a living, from sale of the meat, fur, or some other product, such as ivory.
It was not until Dr. Edwin James' expedition into the Rocky Mountains in 1819-1820 that it was suggested that some parts of the continent should be conserved for wildlife. One of the first to calculate the destruction of wildlife in North America was the artist George Catlin (1796-1872), who studied the Upper Missouri Indians. He was the first American to advocate a national park for people and animals alike. By 1872, it became clear that the plains buffalo had been massacred to the point of near extinction, and Congress established Yellowstone National Park as the first national park in the country.