Final answer:
Agriculture is the subsistence practice that emerged around twelve thousand years ago, marking a significant transition from hunter-gatherer societies and initiating the development of true economies.
Step-by-step explanation:
The subsistence practice that emerged around twelve thousand years ago is agriculture. As human populations transitioned from hunter-gatherer societies, they began actively promoting the growth of crops and the domestication of animals. This pivotal transition marked the beginning of the Neolithic Age and facilitated the development of more settled communities, leading to the first true economies based on raising crops and keeping animals.
Before this shift, humans relied mostly on hunting and gathering, with groups moving constantly in search of food resources. With the domestication of plants and animals, humans were able to adopt a more stationary way of living, allowing for larger populations and the advancement of civilizations.