One of the most curious anomalies of modern western society is that despite all the traditional folklore warnings about dangers to children from step-parents, step-parenting has become a growth "industry", thanks to the growth of divorce and separation. The Cinderella story and its countless variants are cross-cultural and truly international. Clearly experience and concern about the inherent problems of having a non-biological "parent" are very ancient and universal; but is step- parental wickedness just popular fiction? Unfortunately, as Martin Daly and Margo Wilson say, there is evidence to show that having a step- parent "has turned out to be the most powerful epidemiological risk factor for severe child maltreatment yet discovered". Their essay examines this important problem in the light of Darwinian evolutionary theory and particularly the 'selfish gene' concept. Male lions taking over a pride will systematically seek out cubs sired by their predecessors and kill them. This is not pathological behaviour but promotion of their own reproductive success rather than that of their rivals. Furthermore, it has been argued that evolutionary pressures and "natural selection" favour infanticide by replacement males.

Daly and Wilson question whether such models can be applied to humans. Alarmingly they show that a child under three living with a step-parent is about "seven times more likely to become a validated child-abuse case " than one who lives with both genetic parents. However, as they also show, this is not a simple story and there are a number of risk factors involved. The authors are at pains to present the other side of the story: human beings are not lions and child abuse must be considered a "maladaptive by-product of the evolved psyche's functional organisation". After all, adoptive children do not suffer to the same extent.

The authors are both academic psychologists at McMaster University in Canada and have been actively involved in the research into this worrying problem for our society. As they say "how to allocate one's efforts after 'remarriage' is a challenging problem". Since we thrive on positive feedback that enhances our reputations there will be a growing incentive to become attractive exchange partners who are generous and humane. --Douglas Palmer