When did food production and cattle keeping begin in the highlands of Kenya and northern Tanzania?

In the highlands and Rift Valley regions of Kenya and northern Tanzania, food production and the keeping of cattle began in the 1st millennium BCE.1

These practices are believed to have been introduced by peoples who were likely southern Cushites migrating from Ethiopia. Archaeological evidence suggests that agriculture in these areas preceded the development of iron smelting, and hunting and gathering remained a significant component of the domestic economy during this period. It is also possible that the origins of the region's traditional irrigation systems date back to this era.1