This paper focuses on the role of sheep in the agricultural systems from the analysis of situations and Andean Mediterranean, characterized by a strong association between sheep farming and agriculture in the Mediterranean since antiquity, and the introduction of sheep following the Spanish colonization in the Andes. Compared to other domestic animal species in these regions as cattle or Andean camelids, sheep have several advantages (docile, small frame and able to graze difficult areas) that facilitate their livestock. However, their fragility, particularly from predators, forces farmers to collect them at night and invest a lot of work to monitor grazing and lambing. This investment was justified in work until the 19th century by the fact that sheep produced wool, which was often the only monetary income of the family, sometimes milk for family consumption, and realized fertility transfers between space travel (saltus) and cultivated areas (ager, hortus), essential for the production of cereals and tubers, staples of these human populations. The sheep was then a byproduct of this breeding. Only older animals were slaughtered (culls) or very young (animals not kept for herd rebuilding). The opening of the world wool market in the late 19th century signaled the end of this outlet in Western Europe, the development of artificial textiles after World War II led to the decline of the wool industry worldwide and the end of the specific function of sheep as a source of wool. The transfer function of fertility is compromised north of the Mediterranean from 1950 through the use of fertility treatments but continues to play a key role for farmers who can not afford them. Therefore, the question is: under what conditions are sheep, reduced to its function as meat production, viable?