This truly horrible, horrible story makes me very sad. A man kicked a 2 year old girl so hard, in what appears to be a campaign of domestic abuse, that she unfortunately died.

I'm sharing this story with you not just because it makes me sad and angry, or in memory of Amina Agboola, the unfortunate victim, but because my aim here on passle is to share with you an evolutionary biologists view of news and events. I hope to use evolutionary theory to improve our understanding of ourselves, and sometimes disturbing acts like this seem impossible to comprehend, what is the motivation?

We could dismiss the behaviour as that of an evil man, but that isn't very helpful, certainly the behavioural act was evil, but I don't really believe in the usefulness of describing people as either good or evil. Instead I think about how Darwinian evolution produces such acts.

Whenever I read about one of these ghastly stories (thankfully they are quite rare, although remember we only hear about the extreme end of domestic abuse), I check to see if the offending adult was genetically related or not. The media don't tend to focus on this, so the information isn't always easy to find, but nearly always, the offending adult is NOT genetically related to the victim. What is striking is that often there were also genetically related offspring in the same household that were spared the abuse.

This contrast in the treatment between genetically related and non-related offspring is in line with the key tenets of social evolution theory, which basically reduces down to be nice to those that you share genes with. In fact I am writing a paper this week showing that people are more likely to receive help in times of crisis from closer relatives.

Helping is often costly, and the most costly thing we probably do is raise offspring, but these costs are recouped if the offspring are our own, or even just related to us, say our nieces and nephews, because in these cases there is an evolutionary benefit. The genes for such helping behaviours will spread by helping those that are related and thus likely to have the same genes. However, when the offspring are not related to us, we risk expending huge costs (in terms of time, effort, and nowadays money) on someone that will provide no evolutionary benefit. One exception to this is that it may pay to help raise non-related offspring, if in return one gets to mate with the parent and produce genetically related offspring in the future. However this creates selection for deception. One can pretend to be a caring step-parent when the true parent is around, but then turn neglectful and nasty when the true parent is not watching, and this appears to have happened in this unfortunate case.

Now I'm not for one minute saying that these evolutionary considerations entered the mind of the offending step-parent. But over thousands of generations it has been part of the evolutionary consideration, and natural selection operates on these very same calculations.

The result is the evolution can produce individuals that are endowed with mechanisms to guide their behaviour in evolutionary relevant ways. For example, it may be that psychologically such step-parents develop resentment and anger when having to expend energy on step-children. Removing feaces is always going to be a horrible job, and yet parents don't mind nearly so much when it is their own offspring.

Two scientists named Margo Wilson and Martin Daly, among others, have researched this topic (often dubbed the Cinderella effect), for decades. What they have shown is that in general, different forms of homicide can be predicted rather well with evolutionary theory. In particular, they show that infanticide is around 100 times more likely to come from a step parent than a genetically related parent. Long time readers of my passle blogs may remember that my first post was on the evolutionary benefits of infanticide in mammals, such as lions. It appears that humans are no exception.

Of course, an evolutionary analysis is in no way a moral analysis, and evolutionary theory can not be used to show what is right or wrong. What it can do is highlight where a conflict of interests is most likely to occur and to help us better know ourselves. Better the devil you know right?