"Whose Son is He?" joke

About ten years ago, George Bush was visiting Mikhail Gorbachev at the Kremlin. When he got him alone for a moment, he said to Gorbachev, ''Mikhail, can you help me with a problem? I have some doubts about one of the key people under me. How do you decide that someone is smart enough to work for you?''
''Well, when I was interviewing Eduard Shevardnadze, I asked him, 'Eduard, who is the son of your father but not your brother?'''
''What did he say?'' Bush asked.
''He said, 'that's me,' so I hired him.'' Bush patted Gorbachev on the shoulder. ''Thanks, Mikhail. That's a great idea.'' As soon as he got back to Washington, Bush called Dan Quayle over to the White House.
''Dan,'' he said, ''I've got a question for you. Who is the son of your father but not your brother?'' Quayle looked rather puzzled. ''Can I get back to you on that in 24 hours, Mr. President?'' He was very troubled by this question. He kept thinking about it and thinking about it, but couldn't get anywhere. Finally, the thought struck him, ''I'll ask Jim Baker. He's a smart guy.'' Quayle called Baker on the phone.
''Jim, I've got a question for you. Who is the son of your father, but not your brother?''
''That would be me,'' Baker replied. Quayle broke into a big smile.
''Thanks, Jim. You've helped me out big time.'' He went running to the West Wing and burst into the Oval Office. ''Mr. President, I have the answer!''
''Okay, Dan. Who is the son of your father, but not your brother?''
''It's Jim Baker!'' said Quayle.
''No,'' said Bush. ''It's Shevardnadze.''