Darwin referred to evolution as a "struggle for survival". This is often visualised as a struggle between species. However, intraspecies violence is also a key part of evolution. Beating out your competitors can give a huge advantage. So might some species - including humans - evolved a drive for violence?
New research suggests this may be the case. And we might be like this because of our reliance on fish.
Violence evolved
A paper recently published in Nature made a fairly bold claim. Many mammals - including humans - have an innate tendancy towards violence. There's something bubbling in our subconcious. A drive for death produced by millions of years of evolution.
This dramatic conclusion stems from a massive phylogeny the researchers carried out. Essentially, they put all the animals examined in a family tree. They then looked at the rates of violence within those families. If evolution was at work, closely related species should have similar levels of violence. They're all part of the same group, after all.
As their dramatic claim indicates, they found that this prediction was vindicated. Many groups do have a "baseline" of violence. In most species with this violent tendency, this should result in ~2% of the population being killed by members of the same species.
However, this inherited baseline can't explain all cases of intraspecies killing. Some groups fought more than their family history would indicate, others less so. It turns out there are certain factors which can amplify or downplay this innate baseline. These key variables are terretoriality and sociality.
The more terratorial a species is, the more likely they are to get into scraps. More social species also tend to wind up in conflict as well.
Why humans?
There seems to be an essential "baseline" of violence that evolved in many species. Including humans. But this net violence is amplified by our territoriality and intense sociality. But it's not inevitable we turned out that way.
Bonobos are as closely related to us as chimps. Yet they're far less territorial than their more famous counterparts. As a result, murder is rarely witnessed in bonobos. Yet chimps fight so much that there are Wikipedia pages about their wars. Why do we appear to have fallen closer to the chimp side of the scale? Why are we so much more aggressive about our territoriality?
Fish hold the answer.
When you look at all animals a general trend emerges. The hyper-territoriality that can drive human and chimp conflict only appears under certain circumstances. Namely, when the territory contains something within it worth defending.
From that, we can make some inferences about our evolution. At some point in human prehistory, we likely began exploiting a food source that was very valuable. It was rich and predictable, so could be exploited in large quantities. It made life great for those that had it. So naturally, people began fighting over it.
Research has examined the African archaeological record to try and pinpoint that vital resource. The abundant food source that drove humans towards territoriality. It turns out only aquatic resources meet these criteria. People began exploiting rivers, lakes, and coastline from ~160,000 years ago onwards. The food they obtained was rich and predictable, allowing them to exploit it intensley.
Although that might sound like a utopia, it turns out to be a recipie for violence.
Caveats and conclusion
The result of all this research is a comprehensive understanding of why people can be so nasty to each other. Armed with this information, we may be able to improve our conflict resolution. Encourage the better angels of our nature to take hold.
However, before making any dramatic decisions based on this work there are a few caveats. In particular, there are some eyebrow raising issues with the research into our innate level of violence. For example, they predict that most species should kill each other around 2% of the time. Yet they were unable to find a human group that fit that pattern. Modern societies tend to have much lower levels of violence, whilst hunter-gatherers and historical comunities murder each other much more.
The fact this prediction was not vindicated certainly casts some doubt on their claims for an innate "violence baseline". However, it doesn't change the fact they show that territoriality influences violence. And that fish made people territoriality.
So whilst the innate nature of human violence might still be up for debate, the fact of the matter is what violence does occur has its roots in the ocean. And those pesky fishy masters.
References
Gómez, J.M., Verdú, M., González-Megías, A. and Méndez, M., 2016. The phylogenetic roots of human lethal violence. Nature.
Marean, C.W., 2016. The transition to foraging for dense and predictable resources and its impact on the evolution of modern humans. Phil. Trans. R. Soc. B, 371(1698), p.20150239.
