The synthesis of cultural ecology and Marvin Harris's interpretation of Marxist thought is what he referred to as cultural materialism. Harris's argument was one of technological ecological demographic determinism, meaning that technology, ecology, and population growth/density determine other aspects of culture. The hydraulic hypothesis is a cultural materialist approach in that the technology of production is prior to all other aspects of culture. Indeed, for Harris, a key goal of cultural anthropology is to "unlock cultural riddles" by revealing the underlying rational bases for what have in the past been seen as irrational practices. Before examining these differences in closer detail, it bears mentioning that many contemporary Marxist anthropologists, such as Eric Wolf, Scott Cook, and William Roseberry, largely adhere to Marx's original tripartite model of society. Harris challenged the notion that Indian cattle are a wasted or unutilized resource. Most political ecologists challenge other materialist and ecological perspectives that rely on Malthusian "population pressure" as an explanatory device.