Final answer:
The four early river valley civilizations exhibited similarities because they faced comparable environmental challenges and basic human needs that shaped their agricultural practices, societal structures, and governance.
Step-by-step explanation:
The four early river valley civilizations, which developed independently in various parts of the world, still ended up having similarities due to the basic human needs and similar environmental challenges they faced. These civilizations arose along major rivers such as the Nile in Egypt, the Yellow in China, and the Tigris and Euphrates in Mesopotamia, utilizing the fertile land to develop agrarian societies.
The stable supply of food allowed for population stability, which in turn led to the development of a discernible culture, including the emergence of a class of rulers to control wealth and power. This also resulted in an increase in specialized artisans and the creation of monumental architecture. Shared characteristics among these civilizations were due, in part, to similar environmental factors influencing the development of agriculture, governance, and societal structures.