It's an excellent metaphor for humanity's inability to abolish sexual slavery.
Recently, we had the long-overdue full apology by the Japanese Government for the enslavement of up to 200,000 young ‘‘comfort women'' from countries conquered by Japan to provide sexual ‘‘comfort'' to Japanese soldiers during the Second World War.
Prime Minister Shinzo Abe's Government finally ended decades of haggling over the scale of Japan's crime and the form of words in which it should apologise. It simply said we did it and we're sorry, and here's ¥1 billion ($NZ12.43 million) to make restitution to Korea's surviving comfort women.
The apology was a bit late (the 46 surviving Korean ‘‘comfort women'' are all over 80 now), but the mole was well and truly whacked. Except that in another part of the garden, another mole immediately poked his head out of the ground.
This time it was Islamic State. Last Tuesday, Reuters published captured IS documents including Fatwa No64, dated January 29 of last year, which purported to explain the Islamic rules on who may rape a non-Muslim female slave. Or, more precisely, who may not do so (a rather smaller number of people).
An owner may rape his female slaves, of course, but he may not rape both a mother and her daughter. He must make his choice and stick to it.
Similarly, a slave-owning father and son may not both rape the same enslaved woman. And business partners who jointly own a slave may not both rape her. That would be almost incestuous.
This is typical IS provocation, designed to appeal to frustrated young men while simultaneously shocking orthodox Muslim opinion.
And quite predictably, Islamic scholars like Prof Abdel Fattah Alawari, dean of Islamic Theology at Al-Azhar University in Cairo, rushed to point out that IS, in claiming this was part of Shariah law, was deliberately misreading verses and sayings that were originally designed to end slavery.
‘‘Islam preaches freedom to slaves, not slavery,'' Prof Alawari said.
‘‘Slavery was the status quo when Islam came around. Judaism, Christianity, Greek, Roman, and Persian civilisations all practised it and took the females of their enemies as sex slaves. So Islam found this abhorrent practice and worked to gradually remove it.''
Well, yes, but very, very gradually.
Islamic law forbids the enslavement of Muslims, but all that did was to encourage a roaring trade in the enslavement of non-Muslims that lasted for over a thousand years.
And it reached a very long way: when I was growing up in Newfoundand, the easternmost part of North America, we learned in school about the ‘‘Sally Rovers'', Muslim pirates from Morocco who raided villages on the Newfoundland coast for slaves until well into the 18th century.
Muslim slave raids on the Mediterranean coasts of Europe were so constant that long stretches of coastline remained largely abandoned until the 18th century. The last major slave raid by the Crimean Tartars (a traditional revenue-earner known as the ‘‘harvesting of the steppe'') yielded 20,000 Russian and Polish slaves back in the year 1723.
Christianity, which spread widely among slaves in the Roman Empire and did not control any government for the first three centuries of its existence, ought to have done better when it came to power, but it didn't. Slavery lasted in the eastern part of the Roman Empire, Byzantium, until that finally fell to the Turks in 1452.
Slavery had pretty well died out in the Christian West by the year 1000, only to be replaced by the feudal system in which most common people were reduced to serfdom.
And as soon as a demand for actual slave labour reappeared, with the European colonisation of the Americas in the 16th century, the Europeans began to buy slaves from Africa - as the Islamic empires of the Middle East and India had been doing all along.
The longest-lasting source of slaves for the Muslim world was the African trade, both across the Sahara and up from the East African coast, which lasted from the 9th to the 19th century.
Various estimates by historians suggest that between 10 million and 18 million Africans were sold in this thousand-year trade - about as many as were exported by the Europeans in the 250 years of the transatlantic slave trade.
Neither the European empires nor the great Muslim states ended slavery until the 19th century, so there is plenty of blame to go around.
But there is one striking difference between the two trades. The European slavers took two or three African males for every female, because what they wanted was a workforce for commercial agriculture.
The Muslim slavers, by contrast, generally took more women than men, because there was a bigger demand for women as sex slaves (concubines, etc.) than for men as warrior slaves, and practically no demand for agricultural workers.
The Muslim world does have a particular history in the question of sexual slavery, and therefore a particular duty to condemn and fight against the odious doctrinal claims of the Islamic State fanatics.
● Gwynne Dyer is an independent London journalist.
