The culture of Asia encompasses the collective and diverse customs and traditions of art, architecture, music, literature, lifestyle, philosophy, politics and religion that have been practiced and maintained by the numerous ethnic groups of the continent of Asia since prehistory. Identification of a specific culture of Asia or universal elements among the colossal diversity that has emanated from multiple cultural spheres and three of the four ancient River valley civilizations is complicated. However, the continent is commonly divided into six geographic sub-regions, that are characterized by perceivable commonalities, like culture, religion, language and relative ethnic homogeneity. These regions are Central Asia, East Asia, North Asia, South Asia, Southeast Asia and West Asia. As the largest, most populous continent and rich in resources, Asia is home to several of the world's oldest civilizations, that produced the majority of the great religious systems, the oldest known recorded myths and codices on ethics and morality. However, Asia's enormous size separates the various civilizations by great distances and hostile environments, such as deserts and mountain ranges. Yet by challenging and overcoming these distances, trade and commerce gradually developed a truly universal, Pan-Asian character. Inter-regional trade was the driving and cohesive force, by which cultural elements and ideas spread to the various sub-regions via the vast road network and the many sea routes. History Multiple cultural regions Asia's various modern cultural and religious spheres correspond roughly with the principal centers of civilization. West Asia (or Southwest Asia as Ian Morrison puts it, or sometimes referred to as the Middle East) has their cultural roots in the pioneering civilizations of the Fertile Crescent and Mesopotamia, spawning the Persian, Arab, Ottoman empires, as well as the Abrahamic religions of Judaism and later Islam. According to Morrison, in his book Why the West Rules--For Now, these original civilizations of the Hilly Flanks are so far (by archaeological evidence) the oldest (first evidence of farming c9000 BC). The Hilly flanks is also the birthplace of his definition of the west (which groups the Middle East with Europe). According to his definition this would make Asia the origin of western culture. Not everybody agrees with him though. South Asia, India and the Indosphere emanate from the Indus Valley civilisation. The East Asian cultural sphere developed from the Yellow River civilization. Southeast Asia's migration waves of more varied ethnic groups are relatively recent. Commercial interaction with South Asia eventually lead to