Ecological anthropology is a sub-field of anthropology and is defined as the "study of cultural adaptations to environments". The sub-field is also defined as, "the study of relationships between a population of humans and their biophysical environment". The focus of its research concerns "how cultural beliefs and practices helped human populations adapt to their environments, and how people used elements of their culture to maintain their ecosystems". Ecological anthropology developed from the approach of cultural ecology, and it provided a conceptual framework more suitable for scientific inquiry than the cultural ecology approach. Research pursued under this approach aims to study a wide range of human responses to environmental problems. Ecological anthropologist, Conrad Kottak published arguing there is an original older 'functionalist', apolitical style ecological anthropology and, as of the time of writing in 1999, a 'new ecological anthropology' was emerging and being recommended consisting of a more complex intersecting global, national, regional and local systems style or approach. History of the domain and leading researchers In the 1960s, ecological anthropology first appeared as a response to cultural ecology, a sub-field of anthropology led by Julian Steward. Steward focused on studying different modes of subsistence as methods of energy transfer and then analyzed how they determine other aspects of culture. Culture became the unit of analysis. The first ecological anthropologists explored the idea that humans as ecological populations should be the unit of analysis, and culture became the means by which that population alters and adapts to the environment. It was characterised by systems theory, functionalism and negative feedback analysis. Benjamin S. Orlove has noted that the development of ecological anthropology has occurred in stages. "Each stage is a reaction to the previous one rather than merely an addition to it". The first stage concerns the work of Julian Steward and Leslie White, the second stage is titled 'neofunctionalism' and/or 'neoevolutionism', and the third stage is termed 'processual ecological anthropology'. During the first stage, two different models were developed by both White and Steward. "The distinction is not as rigid as some critics have made it out to be, White's models of cultural evolution were unilinear and monocausal, whereas Steward admitted a number of different lines of cultural development and a number of different causal factors. During the second stage, it was noted that the later group agreed with Steward and White, while the other disagreed. 'Neoevolutionists' borrowed from the work