At the core of it are the beginnings of settled life based on animal and plant domestications. Early ideas by Robert Braidwood suggested that there were nuclear zones, that is a region with a natural environment that included a variety of wild plants and animals, both possible and ready for domestication. In truth, not a very useful model . It doesn't tell us why people began to focus on particular species or give us mechanisms to explain it. We must recognize that adaptation is always a local problem.
Selective pressures favor new forms that result from imbalances in the system.
In other words, there have to be reasons for change. Reliability of the food source. Production in adequate quantities to meet population needs. Nutritional requirements must be met in terms of calories, vitamins, minerals. Several models have been proposed that put the selective pressures into operation.