The impact of the show is sinister. There are celebrations here and there, like Katrina Lithgow's exultant studies of pregnant women's bodies or Nick Waplington's series on a wedding party on a Nottingham housing estate. But these are celebrations of the threshold to family, not of the thing itself.
The photographers look on the family as an institution with fascinated horror. For one batch of pictures, caged gorillas at London Zoo were given cameras. They transformed the peering families into glowering primate-groups who are themselves behind bars to be peered at. That item sums the exhibition up.
But I remember another photograph, from the old Lafayette portrait studios, which operated in the 1920s and 1930s. It shows a large Manchester family group, parents and children solidly dressed, some standing, some sitting. They are not handsome. They are all, in fact, quite ugly and not in a picturesque, interesting way either. You would not long to know them.
They are all looking hard at the lens, which means they are looking straight at you, the spectator. On all their faces there is the same peculiar expression. It is expectant. It hints at a smirk. This family is posing a riddle, and waiting for you to solve it. This family has the answer, hidden behind their smirk, but can you guess it? Come on then, lad, we haven't got all day. We'll give you another 20 seconds. Give up?
There came into my head the most famous sentence Tolstoy ever wrote, the first words of Anna Karenina. 'All happy families resemble one another; each unhappy family is unhappy in its own way.' That was the answer. This unattractive, smug bunch of human beings was a happy family. That was their secret. It did not look like a happiness which you could or would want to share, but they were not going to offer you a share anyway. What they had was private. They loved or at least liked one another, and as a team they got on - no doubt on the basis of oppressive, patriarchal rules. Breakfasts, suppers and Sunday lunches en famille could be imagined. Those beefy sons and grave daughters, whatever happened to them in later life, would look back on their Manchester childhood as a good time.
The family - especially the nuclear family - has been roughly treated in the 20th century. In the first years of revolutionary totalitarianism, communist or fascist, the family was perceived as a den of reaction, a burrow down which the citizen might escape. But the ferrets were put in, and the rabbits were chased out into the sunlight of mass parades and Party uniforms. Later, as enthusiasm waned, the dictators rediscovered a use for the family - much the same as the role given to it by factory capitalism. In the home, women fed and reinvigorated men for the next shift, and bred the next generation of workers or soldiers. The family did the basic training in socialist/fascist/Christian morality. Wickedness lived outside, in pubs or on street corners, in shabby halls where people might gather to hold unlicensed meetings or listen to unsuitable pop music. At home, by contrast, nothing unseemly happened. By early evening, the streets of totalitarian cities were deserted.
In the West, as the old working-class culture faded into memory, the 'progressive' view of the family took a quite different tack. It was not a matter of defending the family against the sins which prowled the streets outside. Quite the contrary. The nuclear family was precisely the place where sin and deviance reigned, and behind the demurely closed door began a zone of lawlessness. In the family, children were routinely assaulted by their parents, and women forced into sex they did not want. Lies were told every day with impunity, and stronger children used violence to wrest food or toys from weaker siblings. Blind obedience to commands was expected, for normal civil rights were suspended within the family, and superstitious dogmas were hammered into innocent heads by unscrupulous resort to authority. Murder, rape, the sexual abuse of children and physical assault were crimes committed overwhelmingly at home.
In 1967, Edward Leach summed up the spirit of the age when he said in his Reith Lectures that 'far from being the basis of the good society, the family, with its narrow privacy and tawdry secrets, is the source of all our discontents.' But since then the intellectual pendulum has swung back so far that even radicals now pay their respects to the family shrine.
People talk eagerly about 'one-parent families', anxious that single mothers and fathers should not be excluded from the great institution. Lesbian couples assert their right to be accepted as families, entitled to bear and raise children. The 1960s generation would have been baffled by this emphasis. Their vision of sexual freedom, conditioned only by changing impulses of desire, was not meant to end in a hallway cluttered with big coats and little wellies, closed off from the outside world by a front door with two keys for two partners.
Amitai Etzioni's essay 'The Parenting Deficit', first issued in New York, was published in Britain last year - but by the left-wing Demos think-tank whose founders once edited Marxism Today. It argues that individual choice can no longer be the supreme goal in life. Obligations have to be accepted, and the most important obligation is to surrender a part of personal choice to the duty of parenting. 'Making a child is a moral act,' says Etzioni. 'Children . . . require a commitment of time, energy and above all of self.'
Etzioni insists that the family is being dangerously diluted. Parenting 'requires physical presence. The notion of 'quality time' . . . is a lame excuse for parental absence; it presupposes that bonding and education can take place in brief time bursts, on the run. (But) quality time occurs within quantity time. ' He declares that a family requires two parents, that divorce is always harmful to children, and that the priorities of career and consumption - for men as well as women - must defer to the needs of the 'parenting industry'.
This is Victorian precept repeated as American sociology. And the purpose of it all? 'To bring up children who are better able to form lasting relationships and participate actively in the life of their community'.
Is that what a family is for? It seems too neat a package for that murky, impenetrable little community. Lift the brightly painted lid and the same old 'dear octopus' is lurking, doing things with its tentacles which make an outsider feel faintly sick. 'Happy families resemble one another'. But what makes them happy, and others unhappy, is still a mystery.