The ancestors window shows the current invocation and all its ancestors, and is continuously updated. It can be a very powerful tool in debugging, as it lets you quickly see how variable bindings propagate to ancestor goals. The ancestors window might look like this:
+---+------------------------------------------------------------+
| - | Quintus Debugger Ancestor List |
+---+------------------------------------------------------------+
| File Options Window Help |
+----------------------------------------------------------------+
| (8) 3 : parent(peter2,_749) | |
| (7) 2 : descendant(peter2,_749) | |
| (4) 1 : descendant(peter,_749) | |
| (1) 0 : descendant(henry,_749) | |
| | |
+--------------------------------------------------------------+-+
+--------------------------------------------------------------+-+
Since the ancestors window is updated every time the debugger stops, when there are very many ancestors, you may notice some slowdown in the debugger. In this case, you may wish to close the ancestors window, and only open it when you really need to examine the ancestors. Usually, though, the slowdown caused by having the ancestors window open is small.