Another myth in biology, which is sometimes used to explain murderous and callous behaviour by humans, is the inheritance of a killer instinct. The need by animals to kill is driven by basic needs for food, mates or shelter, an enjoyment in using ones adaptations, and a lack of identification with prey as being anything other than food. These factors alone are sufficient to encourage an animal to learn to kill, and to learn behaviour that becomes interpreted by humans as killer instinct. But conversely, it is also possible for humans not to learn or need a killer instinct.
All animals need food, and many must kill prey to obtain it. The feeling of hunger is sufficient to drive an animal to seek prey. Once they learn what tastes nice, and that ingestion takes away the hunger pangs, predators will continue to hone their hunting and killing skills to find such rewards. Indeed, that is why taste buds evolved, to encourage you to put certain things in your mouth, and why hunger pangs developed, to drive you towards filling your stomach. Predators do not need a killer instinct to tell them to seek prey, as the sensations mentioned above will do the job.
Some other desires may also make an animal kill another, such as a desire for mates or territory. But in by far the majority of cases, death or major injury is not the outcome of these contests, as they are usually resolved by a variety of displays and threatening postures, or tests of strength and prowess. Only for food, is death actually necessary. Killing generally occurs just to the extent needed to deliver a full stomach. After satiation, the need to kill falls away, and there is no need to continue searching for food. The cost in energy, and the risk of injury, will outweigh continued hunting unless there is good reason to continue. In a thriving wild ecosystem, where each organism is operating at its full potential and therefore capable, the balances of various costs and benefits will guide most simple desires, and halt them within reasonable limits.
Under some unusual conditions, surplus killing can occur. The conditions are usually when prey is easily and plentifully available to the predator, and the prey is unable to escape or ignorant of how and why to do so (domesticated). Therefore, the predator can expend negligible energy in the hunt, and kill without the usual risks and costs. The most often used example is when a fox enters a chicken coop and kills all the chickens, when only one was really needed to satiate hunger. There are many other predators that have conducted surplus killing, such as wolves, hyenas, wild dog, bears, weasels, mink, stoat and the domestic cat. Leopard and caracal in South Africa sometimes surplus kill, usually when domesticated stock is trapped against a fence line or within holding pens. Another example was recorded in 29th June 2004 when nine wolves killed 70 sheep in Idaho. A further example was when crows surplus killed young laboratory white mice that had been placed for an experiment upon a bare hill top. Similarly, dodo blithely allowed themselves to be slaughtered without much protest by club wielding sailors, as they had not learnt to fear and avoid such predators.
Surplus killing in pristine environments can also occur, though more rarely. The prerequisite is unusual environmental condition, where escape by prey is difficult compared to the agility of the predator. For example, black-headed gulls in northern Scotland were being killed at the rate of about 200 birds per night by foxes, on several very dark and stormy nights. The gulls did not attempt to fly during such difficult weather, and even human rescuers could pick them up from their nests with ease. Deer herds slowed by deep snow can also be killed by wolves in excess.
Unfortunately, some have interpreted this kind of action as proof of the deep rooted inheritance of a malicious killer instinct. If environmental, then wouldn’t the killing process switch off upon satiation?
There are two learnt reasons for surplus killing, the experience of prey shortage, and the need to hone hunting skills. Prey is sometimes scarce, and most predators would experience hunger at some time, perhaps intensely. Food shortage may be experienced particularly when the predator has a hungry young brood to feed. Therefore, with that memory, a predator will store or cache their killed prey, if given the time to do so. Dogs bury bones, people stockpile food in their pantry, and predators cache their surplus kill. The crows mentioned above cached each of the mice they killed. Foxes usually store and bury their surplus chickens, if not disturbed by the farmer. Foxes can carry only one chicken at a time, so may be disrupted in their progress, but if given time the fox will come back again and again to collect all or most of the killed prey. The excess prey is buried or hoarded for later use. Sometimes, the volume of stored prey may be excessive as well. The predator may not know or have experienced how to judge the quantity of food it needs to store. Additionally, the cached food may spoil before the predator can make full use of it, especially if the predator forgets where it was buried. But these possibilities do not detract from the original logic for surplus killing, which was to store food. In nature, stored food wasted by the predator becomes food for other organisms, so that nothing is really wasted.
A predator may seem additionally wasteful when they only eat the heads or internal organs of the prey, foregoing the rest. However, this pattern can also make sense to the predator, without a need to invoke the killer instinct myth. Why not eat the best and most nutritious bits? The remainder may still be cached at a later date. Alternatively, the remaining carcass not used by the predator will be eaten by other animals and scavengers.
The second and perhaps main reason for surplus killing stems from a need to experience sensation and hone skills. Excess prey can over-stimulate the senses of a predator, as first proposed by Hans Kruuk in 1972 (Surplus killing by carnivores, Journal of Zoology (London). 166:233-244). Learning instincts, honing reflexes, and becoming skilled in your niche are extremely important functions for any animal. Being able to use your claws, senses, and body, and being able to coordinate them all into a tightly honed package, produces a sense of accomplishment or pleasure in the brain’s pleasure centre (more beetle). It means all bodily functions at your disposal have parsimonious and efficient connection. Animals simply follow the pleasures of their stimulations, and cease when interrupted by pain or fatigue. The effect is a bit like a dog that becomes fixated on a ball, and will chase it all day until near exhaustion. The stimulation that the movement gives to the eyes, the pleasure of feeling the agility and skills needed to chase the ball, are all too much to resist. No need for a killer instinct to explain the behaviour, just a desire to feel your body and adaptations in use. Trapped and flapping hens would stimulate a fox a bit like the ball can stimulate a dog. Indeed, chasing behaviour leading to behaviour often interpreted as ‘the killer instinct’ in dogs is more associated with long muzzles than an inherited instinct. Dogs with long muzzles have retinal vision cells organised differently to those in pugs with short muzzles, so that they become more stimulated by peripheral movement, which makes them want to chase. The research of Paul McGreevey and others suggests that rather than hunter instincts being bred into dogs, breeding acted instead upon how the dogs can be stimulated visually. Pugs have better ‘straight ahead’ vision, and as a consequence, will often watch TV, but also, not chase moving ‘prey’ as often simply because the movement may occur outside their peripheral vision.
Similarly, a cat will enjoy clawing at furniture or a carpeted pole, all for the sensation and pleasure of being able to use their attributes and adaptations. It is the movement and stimulation gained from trapped prey, not an inherited instinct, that sends a predator into a spree of surplus killing. So there is no need to make a lion instinctively use its claws, because the positive joys of feeling how the claw works will be enough to produce the neurological linkages needed to meld the coordination of hunting and killing. Curiosity and sensation, rather than a deep seated killer instinct, drives surplus killing.
Similarly, humans might enjoy using their brains, creating art, or playing sport, all for the pleasure of feeling active, alive, and proficient. We don't say that humans have a killer instinct because of their surplus eating of chocolates even when they are not hungry. Some people eat to surplus and become obese. Another example is trying to work out why people spend time bursting bubble wrap. Is it a destructive instinct, or just that the sensation of pressure and pop stimulates several senses at once. To a fox, chooks in a pen are like bubble wrap to humans – callous as this may sound. The fox would like the feelings of what it does, rather than the reason coming from a rule of malevolence or command in the head to kill.
Where can be the bright side or good reason for allowing behaviour to be governed by such seemingly flimsy stimulations? Are animals immoral for such deeds? Why not tarnish them with ‘killer instincts’?
A natural preoccupation for animals is to hone their skills and instincts. That is how they become efficient. Similarly, people enjoy playing games and sport to hone their skills. The benefit of practice is greater ability to prosper and contribute in life. A concentration by predators on honing their killing skills outweighs any environmental problem caused by rare surplus killing events. A predator that practices a little, especially while young, will actually cause less sloppy killing and pain to the bulk of their prey in the future. Many predators have to learn how to quickly despatch prey by going for the throat. Also, any prey that was so incapable and witless as to allow themselves to be trapped and plundered en masse is probably not providing much stability or wisdom to the evolving ecosystem. Nature requires its animals to operate at their full potential, and to become intuitively proficient within their wide variety of niches. The predator would not be used to such stupid behaviour by prey of being trapped in bulk, so would not know how to better utilise or ignore the opportunity. For example, Short found that surplus killing differs between predator-prey systems that have co-evolved over many millennia. Surplus killing is rare between native animals in natural ecosystems in Africa and Europe, compared to the relatively young predator-prey interactions set up between the native fauna of Australia and the introduced fox (where there is a higher incidence of surplus killing by foxes).
Rather than being controlled by inherited instincts, animals develop their codes of behaviour, their ‘morals’, through participation and adjustment with nature. Indeed, instincts are best understood as being the bonded codes of behaviour that develop during a process of attunement learning between animal and niche. If you are not close to your natural niche, the instincts you learn (or don’t realise you learn) will be stunted, twisted and of little value (like human instincts are now). In nature, all an animal usually needs to do to behave appropriately and efficiently within its niche is to follow its senses, use its adaptations, and seek stimulation until pain or fatigue or other information from the niche stops them.
Animals are fairly single minded creatures in the wild, as the best option for them to take is usually readily apparent and there is no real reason to explore indirect possibilities. That is one of the benefits of being so tightly attuned with a niche. What to do becomes obvious. They only need to think of the prey species as food, and seek it out whenever their desire from hunger or an opportunity to hone skills arises. By following a few simple steps (pursue stimulation and pleasure, stop when it gets rough or tough), the animal can hone its instincts and adjust its behaviour to become efficient, according to the feedback it receives from its environment.
Superficially, such an approach may seem self serving and immoral, unless the reader attempts to understand the supporting structure that gives reasons behind such simple-ruled natural behaviours. Then, is the animal acting for itself or to suit the large picture shared by all?
Nature untouched by humans is a wealth of biodiversity, splendour, beauty and good reason. Animals contribute to the development and durability of that ecosystem by being the best that they can be. They achieve this state by attuning with nature, honing their skills, and being efficient. Then, they become a part of the solid foundation of nature. It is a simple sensory approach, but one that works. By being attuned or in partnership with their environment, they gain good reason behind them (something now missed by humans). Sure, they don’t consciously try to please a moral code of good. They don’t need to, because through their practice of remaining open to the contact and feedback available from their environment, they become the embodiment of what is good for that environment.
Another result of the single-minded approach is that wild animals can become trustworthy, reliable and consistent. To me, the scariest creature to come across in the bush or forest is a human. You can never be quite sure about their state of mind, if they have a hidden agenda, and if twisted motives are driving them. A wild animal in the bush is consistent and reasonable, operating from simple pleasures and desires given to them by an environment that I too can understand and feel a part of. It has a reason for being there. Similarly, some people trust their pet dogs more than they can a human.
The point of this essay is to encourage people and biologists to put themselves in animal shoes before judging that the animal path is littered with evil instincts and mental peril, just because some of the behaviours you see are anathema to humans. Animals source their good reason from the wildness (pristine nature). That wildness gives different good reasons to different animals, depending upon their adaptations. That same source, the wildness, might have its own species specific set of instructions and guides for humans as well that will teach them how to become decent animals in their new world. (Posted October 2005)