Beginning in Eurasia, two early innovations had a huge impact on agricultural societies. They allowed people to produce surplus food, and in turn, populations grew in size.

My answer would be the use of farming and the domestication and breeding of animals. Before, people survived the wild by hunting and gathering for their food and clothing. They later learned to grow their own food and instead of hunting animals, learned how to raise them on a certain area. This caused the rise of communities and a growth in population.