Peopling the last new worlds: The first colonisation of Sahul and the Americas

When people set foot in Sahul (Australia and New Guinea) about 50 thousand years ago, they entered a new world which had not seen any species of hominin before. More than 30 thousand years later, people moved into the cold regions of eastern Siberia, across the dry Bering Strait and into North America. In colonizing the north and the Americas they were similarly entering previously unvisited new worlds. The two continents were both colonized only by people who were modern in their biology and their behavior, but the outcomes of those colonizations were rather different. After 50 thousand years or so of human occupation, Australia remained 'a continent of hunter-gatherers' who, for one reason or another, never participated to any great extent in the agriculture that emerged early in the northern part of the continent of Sahul; the Americas, after perhaps 15 thousand years had some hunter-gatherers but also had seen the emergence of agriculture based on its diverse species of plants - an agriculture that spread far beyond the centers of domestication - and at least two of the primary states with complex social hierarchies and urban centers marked by pyramids. What factors contributed to this differentiation?