This book traces the tangled web of intermarriage among a number of Georgian and Victorian families in England: the Darwins and the Wedgewoods, for example, were linked by marriage through several generations. The families which which Kuper deals were prominent indeed, including some of Britain's best known writers, statesmen, bankers, and other influential figures. All practiced endogamy with a vengeance, within the limits of the law---in Britain and in Europe the marriage of first cousins has never been outlawed. Kuper's title, while catchy, is misleading: the marriage of first cousins is not incest except in about five states of the U.S. He discusses few if any incidents of genuine incest (siblings, parent/child, uncle/neice, etc.). He does, however, discuss the family question which most vexed both the Victorians and 19th century Americans: May a man marry his deceased wife's sister?
Kuper is an anthropologist, and has done his work carefully, yet manages to write in an engaging and accessible style. He includes several genealogical charts, but they are laid out in a style which may (or may not) be familiar to anthropologists, but is puzzling to genealogists.
All in all, it's a very interesting and informative read, and gives a good reading of the "back story" of Victorian politicking.