Civilisations arose independently and simultaneously at various rates, in numerous forms and at several locations across, both, the southern and northern hemispheres. They were the result of a transformation in culture. Societies, once nomadic hunter-gatherers, had begun to settle around centres of abundant natural resources. Sedentary societies evolved where people displayed an ability to harness these resources and settled agricultural peoples began to flourish as far back as 12,000 BCE. The indicators of complex social structures emerged. Writing systems were created, tools crafted and domestic products produced; first in stone and then in metal. Animals began to be domesticated.