IN BOXING as in medieval theology, anger is a sin. Lose your rag and you are likely to lose the match. Bite your opponent’s ear off and, as Mike Tyson discovered, you will lose much more.
The animals in Janet Halperin’s laboratory have neither the biceps nor the cerebral skills required for boxing: they are Siamese fighting fish. Yet even these intellectual pygmies seem to fight according to rules. According to Halperin’s research at the University of Toronto, the fish learn their place in the pecking order and react to rivals with a level of aggression that is finely judged for each encounter. Too little brands you as a soft touch, while lashing out at a much bigger rival is seen as just plain stupid.
In the human world most of us use words like “anger” and “aggression” interchangeably, yet there is clearly a difference between impulsive violence and the controlled or premeditated use of force. Both can lead to criminal records, of course. But evolutionarily speaking, it is the impulsive “I just snapped” brand of violence that is hardest to explain. Surely natural selection should have weeded out such obviously maladaptive behaviour?
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To find out why it hasn’t, we need to know what tips the balance between healthy aggression and reckless violence. Thousands of animal and human studies have asked that question, provoking heated (and at times verbally violent) debates about everything from testosterone levels and frontal lobe brain chemistry to mother-son relationships. But there may well be no better place to start than Halperin’s fish tanks. That’s because there are things you can do with fish that would be quite unethical for humans – like turn normal individuals into antisocial maniacs.
The first step is to make the Siamese fighting fish lose sense of where it stands in the pecking order. Halperin and her colleagues achieve this by putting their fish into solitary confinement for a couple of weeks. Then, using mirrors and model fish, the researchers goad the fish for a couple of days. When they finally meet a real rival, the fish thrash around, beating their tails and biting wildly in an exaggerated version of their normal aggressive display. Instead of benefiting from that extra effort, though, Halperin’s fish are much more likely to lose, even to rivals of similar size and strength. “The hyperaggressive fish simply tire themselves out,” she says.
Dead beat
If aggression is an effective way of maintaining social order, reckless violence appears to be a poor survival mechanism – and not just for Siamese fighting fish. Four times a year, Dee Higley and his colleagues at the National Institute of Alcohol Abuse and Alcoholism in Bethesda, Maryland, fly down to a tiny island off the coast of South Carolina to collect fluid samples from the brains and spinal cords of the several thousand rhesus monkeys that roam freely there. The project has been going for almost a decade. And in between the samplings, there’s no let up for the monkeys. Teams permanently stationed on the island keep tabs on specific troupes, monitoring such things as who is mating with whom, which males are dominant, and how the juveniles are shaping up. As a result, the researchers are gradually building up a detailed picture of the biochemical and social factors that lead to monkey violence.
Aggression is a way of life for male rhesus monkeys, but, as with the fighting fish, most know their place in the pecking order and will flee rather than get involved in dangerous fights with bigger or more numerous foe. Some years ago, Higley and his colleagues discovered that a small number of the monkeys, perhaps between 5 and 10 per cent, behave far more impulsively and recklessly. Even as youngsters they were picking fights with large adults and displaying little ability to spar playfully without the situation escalating into violence. Most were cast out of their troupes well before the age most males leave. Many are now dead.
So again, if impulsive violence is maladaptive, why hasn’t natural selection wiped it out? Higley suspects two observations hold the key. The first is that aggression is the work of no one gene or brain chemical or hormone. True, the impulsive monkeys tended to have lower than normal levels of the neurotransmitter serotonin – a factor which has greatly strengthened the idea that this chemical has a role in controlling violent impulses in the brain. Yet the most violent monkeys on the island didn’t just have low serotonin levels, they also had high levels of testosterone. As Higley sees it: “The testosterone is giving them the shove, the drive, but how they express that drive, how well they control it depends on serotonin levels.”
The researchers suspect that while low serotonin levels are disastrous for males, they may be less of a problem for female monkeys. Aggression is less common among groups of closely knit females, as is the risk of social rejection. That raises the intriguing possibility that at least some of the genes which predispose male monkeys to impulsive violence persist because females carry them.
Must Tyson blame his mum, then, for the ear-biting episode? Not necessarily. For while the monkey research continues apace, researchers are still arguing about the role low serotonin and high testosterone levels play in human violence. Most say there is a link between serotonin and impulsive behaviour in humans, but the nature of the link remains blurred. In any case, it is by no means certain that serotonin levels are fixed solely, or even mainly, by your genes. They could also be influenced by nurture, or even by freak environmental events over which we have little control.
Whatever the explanation, if low serotonin is a factor in unrestrained human violence, that is probably because the neurotransmitter is crucial to the normal functioning of the brain’s frontal lobes. Which raises a puzzle. You see, Siamese fighting fish don’t have any frontal lobes.