An ancestor is a parent or (recursively) the parent of an ancestor (for example, a grandparent, great-grandparent, great-great-grandparent, and so forth). Two individuals have a genetic relationship if one is the ancestor of the other, or if they share a common ancestor. In evolutionary theory, species which share an evolutionary ancestor are said to be of common descent. However, this concept of ancestry doesn't apply to some bacteria and other organisms capable of horizontal gene transfer. As… (More on Ancestry)