Historians often trace the dawn of human civilization back 10,000 years, when Neolithic tribes first settled and began farming in the Fertile Crescent, which stretches through much of what we now call the Middle East. Prehistoric peoples domesticated plants to create the cereal crops we still grow today, and in the Zagros mountains of Iran, Iraq and Turkey, sheep, goats and cows were bred from their wild relatives to ensure a steady supply of meat and milk. But around the same time as plants and animals were tamed for agriculture, long before anyone even knew of microscopic life, early humans were domesticating microbes too.