The pursuit of food led the first humans out of Africa and across the continents. Such travel mainly stemmed from necessity. Bands of hunter-gatherers stalked herds and migrated with the seasons as produce ripened. Growth in human populations, fluctuations in climate, and outbreaks of pestilence often led to food shortages, pushing humans further afield. The millions of immigrants to the United States who escaped the Irish Potato Famine of the 1840s, the Finnish Famine of the 1860s, or Russian Famine of the 1890s are recent manifestations of the push and pull factors related to food. Like these refugees from hunger, the Okies – in one of the largest domestic migrations caused by agricultural disaster – abandoned the Dust Bowl of the 1930s in a desperate hope for jobs working the lush orchards and fields of California.