Rice growing in Asia started around 7000 years ago near the Yangtze River. It wasn't just in China - India and Southeast Asia also had rice-growing cultures. Neolithic societies in China evolved quickly thanks to rice, with some becoming advanced enough to build big cities. These early cities were as impressive as any in human history. After these cultures disappeared, the Xia and Shang civilizations showed how important intermarriage was in forming civilizations.