The science of getting your own back

Martha Gill's "Irrational Animals" column.

There’s a fantastic scene at the end of Quentin Tarantino’s film Death Proof. Three young girls are being hunted by Kurt Russell, a psychopath with a stunt car and a foot fetish. We have watched him torture and kill his way through the film, and, as he wends his way towards this group, their naivete is used as a foil to his ever increasing menace. In the last three minutes they beat him to death with an iron pole. It’s a great ending.

Outside Hollywood, the idea of revenge is often pushed into the background, especially when explaining our motives. We call it “justice” or “righting a wrong” or “balancing the scales”, but these notions don’t do much for us biologically, and don’t show up in an obvious way in the brain (it’s a grey area). Revenge, on the other hand, has a very clear neural signal, and that signal is pleasure.

A classic psychology scenario - the prisoner's dilemma - can be combined with neuroimaging to show this quite clearly. In the dilemma, two people have committed a crime and are being held in separate cells. They can either confess and get a reasonable sentence or blame the other, and get a light one. If both blame the other, though, they get the longest sentence of all.

In a study published in 2006, by Tania Singer at UCL, researchers asked two “prisoners” to play this out in front of an audience. Then members of the audience were then put inside fMRI machines while they witnessed each prisoner receiving electric shocks to his hands. As they watched, they showed increased activity in neural pain areas – evidence of empathy. Surprisingly, though, this empathy was present only when watching one of the “silent partners”. If a “confessor” was punished, the activity died down considerably. It looked like the brain cared much less about the pain of those who had betrayed their partner.

There was another finding that Singer didn’t expect. Watching “bad” prisoners get punished gave members of the audience pleasure: there was activation in reward-related areas of the brain, such as the ventral striatum and the nucleus accumbens. (This was limited to male subjects.)

So, we - or at least the men among us - get pleasure from revenge. According to similar studies, we also get activity in the left prefrontal cortex of the brain, which relates to goal planning. Revenge, then, seems to be not only a passing delight, but a craving, something we need, that we plan for. The desire increases when we are mistreated in front of others – we need to show people we’re not to be pushed around – and decreases when we’ve got more to lose by exacting it. In other words, the emotion has a logic to it.

Does it have an evolutionary function? Literature is littered with sayings about revenge and how it never pays, or is better expressed by forgiving the other person, or is exacted by “living well” (with gritted teeth). Yet our neurobiology feels otherwise. Which is right?

Well, let’s return to the prisoner’s dilemma. The dilemma itself is whether or not to trust your partner, but this issue figures only in the beginning. As the game plays out, round after round, prisoners seek petty revenge on each other, punishing the other for betraying them. Eventually, burned out, the two settle on a compromise. And this may be the lesson. Fear of retribution keeps us behaving fairly to others, making co-operation possible. This is why we love watching people get their comeuppance in Singer's test, and why we love watching Quentin Tarantino's films. Revenge is a sweet necessity.

Actress Emily Vancamp from the US drama Revenge. Photograph: Getty Images

Martha Gill writes the weekly Irrational Animals column. You can follow her on Twitter here: @Martha_Gill.

This article first appeared in the 11 February 2013 issue of the New Statesman, Assange Alone

Photo: Getty
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Out with the old: how new species are evolving faster than ever

A future geologist will look back to the present day as a time of diversification, as well as extinction.

Human population growth, increased consumption, hunting, habitat destruction, pollution, invasive species and now climate change are turning the biological world on its head. The consequence is that species are becoming extinct, perhaps faster than at any time since the dinosaurs died out 66 million years ago. This is an inconvenient truth.

But there are also convenient truths. Britain has gained about 2,000 new species over the past two millennia, because our predecessors converted forests into managed woodlands, orchards, meadows, wheat fields, roadsides, hedgerows, ponds and ditches, as well as gardens and urban sprawl, each providing new opportunities.

Then we started to transport species deliberately. We have the Romans to thank for brown hares and the Normans for rabbits. In the 20th century, ring-necked parakeets escaped from captivity and now adorn London’s parks and gardens.

Climate warming is bringing yet more new species to our shores, including little egrets and tree bumblebees, both of which have colonised Britain in recent years and then spread so far north that I can see them at home in Yorkshire. Convenient truth No 1 is that more species have arrived than have died out: most American states, most islands in the Pacific and most countries in Europe, including Britain, support more species today than they did centuries ago.

Evolution has also gone into overdrive. Just as some species are thriving on a human-dominated planet, the same is true of genes. Some genes are surviving better than others. Brown argus butterflies in my meadow have evolved a change in diet (their caterpillars now eat dove’s-foot cranesbill plants, which are common in human-disturbed landscapes), enabling them to take advantage of a warming climate and spread northwards.

Evolution is a second convenient truth. Many species are surviving better than we might have expected because they are becoming adapted to the human-altered world – although this is not such good news when diseases evolve immunity to medicines or crop pests become resistant to insecticides.

A third convenient truth is that new species are coming into existence. The hybrid Italian sparrow was born one spring day when a male Spanish sparrow (the “original” Mediterranean species) hitched up with a female house sparrow (which had spread from Asia into newly created farmland). The descendants of this happy union live on, purloining dropped grains and scraps from the farms and towns of the Italian peninsula. Some of those grains are wheat, which is also a hybrid species that originated as crosses between wild grasses in the Middle East.

This is not the only process by which new species are arising. On a much longer time scale, all of the species that we have released on thousands of islands across the world’s oceans and transported to new continents will start to become more distinct in their new homes, eventually separating into entirely new creatures. The current rate at which new species are forming may well be the highest ever. A future geologist will look back to the present day as a time of great diversification on Earth, as well as a time of extinction.

The processes of ecological and evolutionary change that brought all of Earth’s existing biological diversity into being – including ourselves – is continuing to generate new diversity in today’s human-altered world. Unless we sterilise our planet in some unimagined way, this will continue. In my book Inheritors of the Earth, I criss-cross the world to survey the growth in biological diversity (as well as to chart some of the losses) that has taken place in the human epoch and argue that this growth fundamentally alters our relationship with nature.

We need to walk a tightrope between saving “old nature” (some of which might be useful) and facilitating what will enable the biological world to adjust to its changed state. Humans are integral to Earth’s “new nature”, and we should not presume that the old was better than the new.

“Inheritors of the Earth: How Nature Is Thriving in an Age of Extinction” by Chris D Thomas is published by Allen Lane

This article first appeared in the 20 July 2017 issue of the New Statesman, The new world disorder