There is another wild card to take into account in history: the way that something which once seemed so important to everyone can suddenly seem of no significance at all – and then all the worries are rapidly forgotten, as if they had never been. Let me point you to one of the most long-lasting examples: the Christian ban on menstruating women from participation in the sacraments or even from approaching the altar.

This prohibition, which seems so bizarre now, is first to be encountered in the writings of Dionysius, bishop of Alexandria at the beginning of the third century. An honourable exception – one of very few – to this unexamined consensus was Pope Gregory the Great, writing soon after launching his mission to England under the monk Augustine in 597. Alas, the pope’s open-mindedness was probably conditioned by his evident irritation with the Christians already in Britain before Augustine arrived; they not only predated but resisted Augustine’s authority. These native Christians were rigorous about menstruating women and it was their independent-mindedness that provoked the pope’s liberal ruling. The consensus began to fade in the 16th-century Reformation, at least among those Protestant churches whose worship was less centred on the sacraments than was the case in the Catholic church, but the prejudice survived half-expressed in the more ceremonially minded parts of Lutheranism and Anglicanism until the 1950s and it could still be encountered in 1970 in a regulation of the Catholic church excluding women lectors from the sanctuary during their menstrual periods. Now western Christendom at least has forgotten an issue on which church leaders were near-unanimously agreed, almost without discussion, for 1,700 years. Any lessons to be drawn from that? I have to admit that I had never heard of this.