It's rare for the leader of a country to die in office. Since 2008, it's happened 13 times worldwide - but 10 of those leaders have been African. Why is it so much more common in this one continent?
So, four African leaders have died in office this year alone. Disruptive for the countries concerned, tragic for the leaders' families. But spare a thought also for the reporters.
It's certainly true that leaders are dying in office in higher numbers in Africa than on any other continent. In the same period, only three other national leaders have died in office - Kim Jong Il of North Korea, Polish President Lech Kaczynski, who died in a plane crash, and David Thomson of Barbados, who had cancer.
The obvious answer is that African leaders are just older than those of other continents - respect for elders is embedded in the culture of many of the continent's countries. But are they, really?
Serving leaders' average ages (figures for heads of executive power, whether this is president, prime minister, or monarch):
Actually, as clearly seen from the table above, the average age of African leaders is 61 years - the same as in Asia. European leaders are, on average, 55 years old, while in South America, it's 59.
But another thing to consider is life expectancy which, among the general population, is lower in Africa than in Europe, Latin America and Asia. This is partly because of problems like the prevalence of HIV/Aids and also poor medical care, which leads to high rates of death in childbirth.
But poverty in childhood and early life can also have a lasting impact, as Dr George Leeson, a gerontologist from the University of Oxford, explains.
"African presidents, before they have been elected, will have led a relatively disadvantaged life, and disadvantageous lifestyle, and that will impact on their life expectancies at subsequent ages," he says. "So, once they get into the presidential office, even though they will be living a lifestyle far far far removed from their fellow citizens, which would increase their life expectancy in relation to those fellow citizens, they do have an accumulated disadvantageous lifestyle which they have to pay back on at some time."
Although of course, not all African leaders will have had poor childhoods.
But is there another factor to take into account - politics? The stereotypical African leader clings on to power until he drops. But the facts don't seem to fit that explanation.
"This is true of some of the leaders who died in office, particularly Omar Bongo, Conte and Gaddafi," says Simon Allison. "All of them were old-school dictators who were never going to leave voluntarily, but the others are different - Meles Zenawi had clung on to power for a long time, but he was only 57. And all the others were in their constitutional time limits and hadn't even fiddled with them yet."
But whatever's going on, such a death toll creates uncertainty. Deaths in office create power vacuums, which can be dangerous and destabilising.
"Look at what happened in Guinea-Bissau," says Simon Allison. "When Sanha died, a coup followed very shortly afterwards. This is a difficult situation for Africa to find itself in because it, historically, has not done very well with power vacuums."
However, he believes there is some cause for optimism.
"In Zambia, in Malawi and Ghana and in Nigeria, the death of the president was followed by a constitutional succession with a minimum of violence and dispute, and I think this is a very encouraging sign for Africa's development."