Around 6500 BCE, agriculture emerged in Balochistan, on the margins of the Indus alluvium. In the following millennia, settled life made inroads into the Indus plains, setting the stage for the growth of rural and urban human settlements. The more organized sedentary life, in turn, led to a net increase in the birth rate. The large urban centres of Mohenjo-daro and Harappa very likely grew to containing between 30,000 and 60,000 individuals, and during the civilization's florescence, the population of the subcontinent grew to between 4–6 million people. During this period the death rate increased as well, for close living conditions of humans and domesticated animals led to an increase in contagious diseases. According to one estimate, the population of the Indus civilization at its peak may have been between one and five million.