In the late nineteenth century evolutionary theories shaped anthropological thinking about society's development and the diffusion of innovations like agricultural production, which was framed as a natural progression from hunter-gatherer lifeways. Cultural ecology models of the 1950s looked at functional relationships between the environment and adaptation, interpreting cultural traits as homeostatic systems that ensured equilibrium between people and their environment. Political economy analyses in the mid-twentieth century countered the notion that agriculture development arose from the environment, focusing rather on the role that human labor and other social factors played in driving agriculture. In the late twentieth century critiques of power and of discourses that depicted indigenous agricultural systems as backward emerged. Recent years have seen a focus on resistance to an increasingly globalized food system through analysis of food sovereignty and organic and fair trade agriculture, as well as the role of a changing climate in driving agricultural change.