Long-term relationships in a society where people generally lived for at least three and a half centuries were necessarily of a different nature from those in the more primitive civilisations which had provided the Culture’s original blood-stock. Life-long monogamy was not utterly unknown, but it was exceptionally unusual. A couple staying together for the duration of an offspring’s entire childhood and adolescence was a more common occurrence, but still not the norm. The average Culture child was close to its mother and almost certainly knew who its father was (assuming it was not in effect a clone of its mother, or had in place of a father’s genes surrogated material which the mother had effectively manufactured), but it would probably be closer to the aunts and uncles who lived in the same extended familial grouping; usually in the same house, extended apartment or estate.

There were partnerships which were intended to last, however, and one of the ways that certain couples chose to emphasise their co-dependence was by synchronising their sex-changes and at different points playing both parts in the sexual act. A couple would have a child, then the man would become female and the woman would become male, and they would have another child. A more sophisticated version of this was possible due to the amount of control over one’s reproductive system which still further historic genetic tinkering had made possible.

It was possible for a Culture female to become pregnant, but then, before the fertilised egg had transferred from her ovary to the womb, begin the slow change to become a man. The fertilised egg did not develop any further, but neither was it necessarily flushed away or reabsorbed. It could be held, contained, put into a kind of suspended animation so that it did not divide any further, but waited, still inside the ovary. That ovary, of course, became a testicle, but - with a bit of cellular finessing and some intricate plumbing - the fertilised egg could remain safe, viable and unchanging in the testicle while that organ did its bit in inseminating the woman who had been a man and whose sperm had done the original fertilising. The man who had been a woman then changed back again. If the woman who had been a man also delayed the development of her fertilised egg, then it was possible to synchronise the growth of the two fetuses and the birth of the babies.

To some people in the Culture this - admittedly rather long-winded and time-consuming - process was quite simply the most beautiful and perfect way for two people to express their love for one another. To others it was slightly gross and, well, tacky.