A painstaking analysis of homicides around the world reveals that natural selection can explain why certain categories of people stand a greater chance of being murdered than others, according to Martin Daly and Margo Wilson of McMaster University in Hamilton, Ontario.
Modern Darwinists propose that animal behaviour has evolved to ensure the survival of an individual's genes through the generations. Professor Daly and Dr Wilson propose that Darwinian theory can identify those groups most likely to commit murder.
Home Office criminologists are apparently divided but, according to the two scientists, are sufficiently impressed by the apparent robustness of the Darwinian model for predicting murder to take the research seriously.
Daly and Wilson claim their research is the first attempt to place homicidal behaviour into a Darwinian perspective. Conventional views on criminology, they believe, do not take account of genetically programmed 'psycho- sociological mechanisms' that have evolved over hundreds of thousands of years to give individuals a selective advantage.
At a conference that ended yesterday at the London School of Economics, they cited several instances where who killed whom fitted predictions based on Darwinian theory.
Darwinism, for instance, predicts that genetically related individuals will co-operate against competing, unrelated individuals. Daly and Wilson say this means that two collaborating murderers are likely to be more closely related than victims are to their killers: data from around the world shows this is indeed the case.
Natural selection favours the male lion who kills the cubs of lionesses he has taken over from another male. Daly and Wilson believe that the relatively large number of step-parents who murder their step-children is a form of aberrant behaviour resulting from similar selection pressures in early human history.
Professor Daly said they have looked at every other conceivable factor to explain the higher risk of step-parent/step-children murders, such as poverty, family size, and the possibility that step-parents, as a group, are just more prone to violence.
'None of these work. The step relationship is a discrete risk factor and this is a widespread phenomenon in different societies around the world,' he said.
The two researchers also analysed murders of women by their husbands and found the results match Darwinian predictions about males ensuring their female mates' fidelity. Dr Wilson said such murder is the aberrant by- product of a man's deep-seated desire to ensure his wife is faithful.
'Controlling a wife may very well have served male interests in monopolising reproductive capacity in our evolutionary past,' she said.
In a large majority of cases, men kill their wives after accusing them of adultery, Professor Daly said. 'Women who kill their husbands usually do so in defence of their children or themselves.'
Darwinian theory also predicts that male concern about adultery will be more intense the younger the female partner is, because there is more reproductive potential at stake.
Translated into human homicides, this predicts that younger wives are more likely to be murdered by their husbands than older wives, which is exactly what Daly and Wilson found. Sceptics will argue that younger wives are more likely to be married to younger men, who are in general more violent than older men. However, the researchers found that older men married to young women are even more likely to murder them.
In Darwinian terms, it makes no sense for a parent to kill their biological children, so why does it happen at all? Daly and Wilson stress that murder is not the adaptation evolved through natural selection, but the pyschological condition that in certain circumstances can be tipped into aberrant patterns of behaviour.
Nevertheless, Darwinian theory predicts that biological parents should be less likely to kill children as they get older, because of the increasing reproductive effort that has been 'invested' in them. Again, they found the data agrees.
'People say you don't need any of this fancy theory to predict that people are less likely to kill their kids as they get older because they (the children) just get harder and harder to kill,' Professor Daly said. But if this was true, he said, it cannot explain why non-relatives are more likely to kill older children.
Dr Wilson said the value of using Darwinian evolution to understand homicides is to identify risks better and intervene 'before someone gets killed'.