The dialogue between anthropology and archaeology with respect to the possible social organization of early Sahul (Australia – Papua New Guinea) migrants 50,000 years ago has been close to inexistent. The reason lays in the fact that anthropology has implicitly or explicitly favoured symmetry and closeness (and reciprocity of exchanges) as being fundamental and historically ancient features of human social organization. Through the definition and ethnographic illustration of what I call “open” and “closed” systems, this paper illustrates that asymmetry and openness are far better adaptations in conditions where social and material resources are unpredictable. Engaging in an additional dialogue with evolutionary ecology, it is suggested that the distinction between “closed” and “open” systems also reflects a qualitative jump from inclusive fitness to indirect reciprocity. The combination of the anthropological analysis with archaeological findings and with theory of evolutionary ecology demonstrates that many Australian Aboriginal peoples know open systems that favour the diversification of interrelationships and resources, rather than the repetition of existing exchange relationships. This model is also more accurate to envisage the kinship structure and social organization of the early migrants to Sahul.