How much do you really want to know about your family history?  What if you discover an ancestor that led a life incompatible with your morals.  What if you find a criminal, an abuser, or a racist? In the book, American Tapestry, Rachel Swarns explains how Michelle Obama's family tree includes a slave owner named Henry W. Shields, and an enslaved woman named Melvinia.  Shields' son Charles is mos…