tokens: Evidence of drainage ditches at Kuk Swamp on the borders of the Western and Southern Highlands of Papua New Guinea shows evidence of the cultivation of taro and a variety of other crops , dating back to 11,000 BP. Two potentially significant economic species , taro ( " Colocasia esculenta " ) and yam ( " Dioscorea " sp. ) , have been identified dating at least to 10,200 calibrated years before present ( cal BP ) .