Perhaps the evidence that's been most attacked is the 1408 map itself. Dr. Geoff Wade, a historian with the National University of Singapore, has written extensively in an effort to debunk Gavin Menzies and the 1421 theory, even going so far as filing a complaint in the United Kingdom against the publishers of Menzies' book for marketing it as a history.
Wade points out several flaws with the 1408 map which suggest it's a fake, chief among them is that the map shows the world based on the idea that it's a sphere. This notion was unknown in Ming Dynasty China. He also points out that China is poorly represented on the map, and wonders why, if the map's creators were Chinese, their nation would be drawn clumsily.
It's Wade's belief that the 1408 map was created within the 21st century, possibly even to support Menzie's 1421 theory. Wade believes that the map is based on old maps created by Jesuit missionaries in the 17th century. He points out that California is shown as an island and China is located at the center of the map, both examples of Jesuit cartography. He also says that some of the text has clearly been translated into Chinese from old Jesuit maps.
If the map is fake, then the entire 1421 theory falls apart. But isn't there any easier way to determine if the Chinese ever sailed to the Americas? Why not just ask? Here's where the story takes a turn that may maintain the 1421 theory's status as debatable for years to come. After the invading Manchu rulers took over China following the Ming Dynasty (establishing the Qing Dynasty), the foreigners took great pains to wipe out any reminders of the previous rule. This included destroying all accounts of the great fleet's extensive voyages. As these documents burned, any evidence, contradictory or supportive, of a Chinese presence in the Americas was lost forever.
For more information on maps, as well as links to Menzies' and Wades' discourse, visit the next pages.