Evolution and homicide: Is homicide adaptation theory a valid evolutionary theory?

Homicide is an umbrella term that describes an action by a human, which results in the death of another. This can be accidental (Manslaughter) or intentional/pre-meditated (Murder). Homicide adaptation theory (HAT), proposed by Buss and Duntley was developed to explain why humans commit homicide, and theorises that humans have ‘evolved psychological mechanisms that facilitate the killing of another human in certain contexts where this act would solve recurrent adaptive problems throughout human history’. HAT is an evolutionary theory, which means it explains that behaviour (in this case homicide) is caused by changes in characteristics over time. Otherwise known as natural selection. Natural selection produces adaptations which increase the reproductive fitness of the individual in the context they evolved in. For HAT to be a valid evolutionary theory there must be evidence that the traits proposed are a result of natural selection. A fundamental concept in evolution is that for an adaptation to evolve the benefits of it must outweigh the costs at the time it evolved. The homicidal traits suggested by HAT are beneficial because they would increase reproductive fitness, for example, by removing someone from the social hierarchy, the individual will have more choice of mate and so be more likely to reproduce. Duntley and Buss evidence patterns of homicide as support for HAT, referring to the majority of homicide cases in which the context of the crime would have had benefits in human history. For example, killing rival mates or unfaithful spouses. This would support the idea that homicide evolved due to similar historical circumstances. However, it can be argued that HAT provides insufficient evidence or detail on the relative costs of homicide in historical contexts thereby giving a false image of the balance between costs and benefits. For example, killing a rival may increase the likelihood of retribution of their kin or group. Similarly, intraspecific homicide may impact the success of the group, consequently decreasing the individual’s reproductive fitness. These potential costs and several others have not been thoroughly considered by Dudley and Buss, meaning there is a lack of evidence to support that the traits proposed by HAT are adaptations resulting from natural selection, because in these situations the costs of homicide could have outweighed the benefits. This would therefore mean HAT cannot explain homicide in terms of evolution and natural selection. Another key idea in HAT is the evolved special design features. These features are what provide evidence that an adaptation has occurred and so without significant evidence for them HAT can’t be supported as being an adaptive theory. Duntley and Buss suggest humans have ‘evolved psychological mechanisms which allow homicide to occur’. They support this claim by referencing homicidal ideation. According to a study by Kenrick and Sheets, 70% of participants reported experiencing homicidal ideation at some point in their lives. Additionally, these fantasies mostly occurred in situations where homicide would have likely solved an issue which supports the idea that homicide is adaptive. Furthermore, Duntley and Buss use the comparative method, noting that many other species display homicidal tendencies in specific situations and conclude that this can support the idea that humans may also have adaptations for homicide. The comparative method is commonly used by evolutionary psychologists however Duntley and buss have been criticised in their use of it. In their research they mention the Black Widow Spider whose females with kill and eat their male partner after copulation. However, this cannibalistic killing in this situation does not compare in any way to human homicidal patterns. Their choice of species to compare for traits cannot accurately reflect the potential of humans to have the same evolved adaptations, which suggests there is no support that HAT is a valid evolutionary theory. To conclude, the evidence and detail provided by Duntley and Buss in support for homicide adaptation theory is very limited and so cannot fully support the idea that homicide is an adaptive, evolved behaviour. For HAT to be a credible evolutionary theory for explaining why people commit homicide, more evidence and research needs to be done to support the proposed special design features and idea that these features are adaptive.