I’m dipping into (“reading” is too organised a concept for my random excursions) This Explains Everything: Deep, Beautiful and Elegant Theories of How the World Works, edited by John Brockman. This is a collection of almost 150 short essays written in response to the Edge question of 2012: What is your favourite deep, elegant, or beautify explanation?
The answers cover the spectrum from particle physics through psychology to the social sciences. Authors include luminaries like Susan Blackmore, Leonard Susskind, Stephen Pinker, Carl Zimmer and Jared Diamond as well as a whole host of people I’ve never heard of.
One essay I read last evening stood out for me, and I am naughtily going to reprint it here in its entirety.

The Overdue Demise of Monogamy
Aubrey de Gray
Gerontologist; chief science officer, SENS Foundation; author, Ending Aging
There are many persuasive arguments from evolutionary biology explaining why various species, notably Homo sapiens, have adopted a lifestyle in which males and females pair up long-term. But my topic here is not one of those explanations. Instead, it is the explanation for why we are close — far closer than most people, even most readers of Edge, yet appreciate — to the greatest societal, as opposed to technological, advance in the history of civilization.
In 1971, the American philosopher John Rawls coined the term “reflective equilibrium” to denote “a state of balance or coherence among a set of beliefs arrived at by a process of deliberative mutual adjustment among general principles and particular judgments.”* In practical terms, reflective equilibrium is about how we identify and resolve logical inconsistencies in our prevailing moral compass. Examples such as the rejection of slavery and of innumerable “isms” (sexism, ageism, etc.) are quite clear: The arguments that worked best were those highlighting the hypocrisy of maintaining acceptance of existing attitudes in the face of already established contrasting attitudes in matters that were indisputably analogous.
Reflective equilibrium gets my vote tor the most elegant and beautiful explanation, because of its immense breadth of applicability and also its lack of dependence on other controversial positions. Most important, it rises above the question of cognitivism, the debate over whether there is any such thing as objective morality. Cognitivists assert that certain acts are inherently good or bad, regardless of the society in which they do or do not occur—very much as the laws of physics are generally believed to be independent of those observing their effects. Noncognitivists claim, by contrast, that no moral position is universal and that each (hypothetical) society makes its own moral rules unfettered, so that even acts we would view as unequivocally immoral could be morally unobjectionable in some other culture. But when we make actual decisions concerning whether such-and-such a view is morally acceptable or not, reflective equilibrium frees us from the need to take a view on the cognitivism question. In a nutshell, it explains why we don’t need to know whether morality is objective.
I highlight monogamy here because, of the many topics to which reflective equilibrium can be usefully applied, Western society’s position on monogamy is at the most critical juncture, Monogamy today compares with heterosexuality not too many decades ago, or tolerance of slavery 150 years ago. Quite a lot of people depart from it, a much smaller minority actively advocate the acceptance of departure from it, but most people advocate it and disparage the minority view. Why is this the “critical juncture”? Because it is the point at which enlightened thought-leaders can make the greatest difference to the speed with which the transition to the morally inescapable position occurs.
First let me make clear that I refer here to sex and not (necessarily, anyway) to deeper emotional attachments. Whatever one’s views or predilections concerning the acceptability or desirability of having deep emotional attachments with more than one partner, fulfillment of the responsibilities they entail tends to take a significant proportion of the twenty-four hours of everyone’s day. The complications arising from this inconvenient truth are a topic for another time. In this essay, I focus on liaisons casual enough (whether or not repeated) that availability of time is not a major issue.
An argument from reflective equilibrium always begins with identification of the conventional views, with which one then makes a parallel. In this case, it’s all about jealousy and possessiveness. Consider chess, or drinking. These are rarely solitary pursuits. Now, is it generally considered reasonable for a friend with whom one sometimes plays chess to feel aggrieved when one plays chess with someone else? Indeed, if someone exhibited possessiveness in such a matter, would they not be viewed as unacceptably overbearing and egotistical?
My claim is probably obvious by now. It is simply that there is nothing about sex that morally distinguishes it from other activities performed by two (or more) people collectively. In a world no longer driven by reproductive efficiency, and presuming that all parties are taking appropriate precautions in relation to pregnancy and disease, sex is overwhelmingly a recreational activity. What, then, can morally distinguish it from other recreational activities? Once we see that nothing does, reflective equilibrium forces us to one of two positions: Either we start to resent the temerity of our regular chess opponents playing others, or we cease to resent the equivalent in sex.
My prediction that monogamy’s end is extremely nigh arises from my reference to reproductive efficiency above. Every single society in history has seen a precipitous reduction in fertility following its achievement of a level of prosperity that allowed reasonable levels of female education and emancipation. Monogamy is virtually mandated when a woman spends her entire adult life with young children underfoot, because continuous financial support cannot otherwise be ensured. But when it is customary for those of both sexes to be financially independent, this logic collapses. This is especially so for the increasing proportion of men and women who choose to delay having children until middle age (if then).
I realize that rapid change in a society’s moral compass needs more than the removal of influences maintaining the status quo; it also needs an active impetus. What is the impetus in this case? It is simply the pain and suffering that arises when the possessiveness and jealousy inherent in the monogamous mind-set butt heads with the asynchronous shifts of affection and aspiration inherent in the response of human beings to their evolving social interactions. Gratuitous suffering is anathema to all. Thus, the realization that this particular category of suffering is wholly gratuitous has not only irresistible moral force (via the principle of reflective equilibrium) but also immense emotional utility.
The writing is on the wall.
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* A Theory of Justice (Cambridge, MA: Belknap Press, 1971).

Friends with benefits. Or just friends. Or just benefits. Where’s the problem?
As one of my university friends used to observe: why should sex not just be an expression of friendship; we have sex just because we’re friends and feel like it; no more, no less? How is this actually different from having a drink, listening to records, or playing tennis together?
I’ve always struggled to see why anyone has a problem with this.