The Science of Discworld II

to. There is a factor that Moses and his colleagues didn’t explicitly consider, and it needs to be explained away, because it makes those figures much too good.
    Most human groups pretend to practise monogamy, but like swansand gibbons and other creatures that we thought were faithful for life, there are plenty of adulterous relationships and children ‘whose legal and biological parentage differ’. In English society, about one child in seven is in that position, and the proportion doesn’t differ much between the slums of Liverpool and the stockbroker belt of Maidenhead. 6
    The most restrained people that we know, in this regard, are the Amish of Eastern Pennsylvania and other parts of the United States, for whom the figure is a mere one in twenty. So, to err on the safe side, let’s assume that all of the Mrs Cohens, from the present day back 100 generations to the sons of Aaron, were as well behaved as the Amish. Then the proportion of Cohen males with Aaron’s Y-chromosome should be 0.95 100 , which is considerably less than one in a hundred. So how can it be as high as one in two?
    There is a possible explanation, consonant with what we know about human sexuality, or at least with what John Symons, an expert on human sexual practices, says in his books. According to many surveys of sexual behaviour, going right back to Alfred Kinsey around 1950, women practise adultery with men of both higher and lower status. The two situations frequently occur in different social contexts, with women ‘doing favours for’ higher status men (think Clinton), but going down-market for ‘a bit of rough’. Overwhelmingly often, however, when a baby results the father is of higher status than the woman’s husband or regular partner.
    This implies that if Mrs Cohen, living in a ghetto or any other pre-dominantlyJewish society, wants to go up-market, her only choices are other Cohens. So the maintenance of the Aaron Y-chromosome may have been assured by sexual snobbery rather than amazing fidelity, and that’s a much more likely story.
    1 This is why we have been forced to invent differences of religious belief, which give us an excuse to kill each other because They are so dramatically different from us True Human Beings – they don’t even know that spilling salt, and then failing to hop three time around the table, invites a demon into your home. So it’s all right to wipe the False Humans, Them, from the face of the planet.
    2 The! is a symbol denoting a particular clicking sound.
    3 A meal that should see you through the week, as the old music hall joke reminds us.
    4 Lakes Malawi and Tanganyika still have their cichlid species flocks; your local tropical-fish shop will have representatives.
    5 ‘Going walkabout’ seems to have been a way to avoid this torture for at least some Australian tribes.
    6 Yes, we know you don’t believe this, but … The first reliable data are in Elliott Philipp’s analysis of blood-groups from families in high-rise apartments in Liverpool in the late 1960s, published in 1973. There, 10 per cent of the ‘legal paternities’ were biologically impossible. So, correcting for the cases where the milkman had the same blood-group as the legal father, about 13–17 per cent were ‘discrepant paternities’, as the coy phrase goes. Hundreds of births in Maidenhead, in the stockbroker-belt, yielded the same proportions. American figures for the 1980s were about 10 per cent, but these were underestimates because they were not corrected as above. That’s the thing about science: it tells you stuff you didn’t expect. It gets worse. Or maybe you feel it gets better. At any rate many animals that until recently were famed for their fidelity, such as swans, turn out to be partial to a bit on the side. That ubiquitous beast, the monogamus, is rapidly going extinct.

THIRTEEN
STASIS QUO
    T HE BREEZE SHOOK THE WILLOWS . And, in the centre of the willows, the lightning-struck tree spoke, in a very faint voice. The Ugs had seen lightning strike the same tree three times. It was the highest point in the area, thanks to the shell mounds.
    Even for creatures so preternaturally against thinking any kind of new thoughts, this made an impression. In some way, they’d felt, the tree had importance. It was an important thing. The place of the tree was an important place, where the sky touched the ground.
    It