The history of the domestication of cotton is very complex and is not known exactly.[1] Several isolated civilizations in both the Old and New World independently domesticated and converted cotton into fabric. All the same tools were invented, including combs, bows, hand spindles, and primitive looms.[2]:11–13 The oldest cotton textiles were found in graves and city ruins of civilizations from dry climates, where the fabrics did not decay completely.[3] Some of the oldest cotton bolls were discovered in a cave in Tehuacán Valley, Mexico, and were dated to approximately 5500 BCE, but more recent estimates have put the age of these bolls at approximately 3600 BCE. Seeds and cordage dating to about 450BCE have been found in Peru. There is reliable genetic evidence that cotton originated in Peru. At the source of any plant—in this case wild cotton, the genetic variability is enormously greater and one area of wild cotton in Peru constitutes a "smoking gun.".[1][4] The Indus Valley civilization started cultivating cotton by 5th or 4th century BCE. By 3000 BCE cotton was being grown and processed in Mexico, and Arizona. Pre-Incan cotton grave cloths were found in Huaca Prieta in Peru, and date back to 2500 BCE, and cotton was mentioned in Hindu hymns in 1500 BCE