Many countries have a president and a prime minister. In Poland these two positions are currently held by identical twins - Lech and Jarosław Kaczyński.
Some people might think this arrangement defeats the object of having a separation of powers between the two positions. Just as good corporate governance supposedly entails a separation between chairman and chief executive. Putting identical twins into the two posts is somehow cheating.
I don't know if there are any major corporations governed by twins - but there are certainly some major corporations governed by families. See discussion on the Murdoch family: Trust and Conflicts of Interest, The Price of Trusting Murdoch, Who Trusts James Murdoch?)
What about governments and large companies run by friends, or people with shared backgrounds? There are many examples of this. Is it healthy? Is political friendship a good thing?
Sometimes it seems as if it is very important. One of the constant topics of those watching the UK Labour Government over the past ten years has been the state of the personal relationship between Tony Blair and Gordon Brown. As if the well-being of the nation depended not just on the ability and determination of the two men, but also their friendship. The collective fantasy that the government - indeed the entire nation - would collapse if these two men were unable to sustain their supposedly fragile alliance - has merely reinforced their power.
But at the same time we are suspicious of friendship. Tony Blair was criticized for giving key posts to his friends - Tony's cronies they were called - from the Lord Chancellor downwards. And of course this phenomenon is commonplace in other countries. (Dick Cheney was chairman and chief executive of Halliburton. Need I say more?)
Perhaps the most egregious example in modern times is the government of Harold Macmillan. As Andrew Marr points out in his recent TV series, The Making of Modern Britain, Macmillan handed out dozens of senior government jobs to friends and family. And then when things went wrong he sacked most of them in what became known as The Night of The Long Knives. As Jeremy Thorpe said at the time, "greater love hath no man than this, than to lay down his friends for his life".