Animals and the Nature of Feeling Good
By Jonathan Balcombe
Macmillan Copyright © 2006 Jonathan Balcombe
All rights reserved.
SURVIVAL OF THE HAPPIEST
The adaptive basis for pleasure
Science has neglected animal pleasure. Scientists like 'the big picture.' Research tends to focus on evolutionary explanations for natural phenomena. By considering only natural selection and reproductive success, it overlooks the experiences of individuals – their feelings, emotions, pleasures.
To appreciate the importance of pleasure to survival, consider the interplay of evolution and experience. Evolution concerns the adaptiveness of what an animal does (or doesn't do). It is the stuff of genes and survival. Experience, on the other hand, relates to an animal's conscious, sensory encounters with the world.
Evolution and experience are complementary, not exclusive. Just as an animal is the product of genetics and environment, so too do both evolution and experience guide decisions and behaviors. When an animal – let's say a raccoon – eats, she is satisfying a basic need of survival: to sustain herself. But in choosing, seeing, smelling and tasting food, she also experiences it. The physical pleasures of life – like the pains – are current, even though they have evolutionary significance. It is these experiences, not the evolutionary forces underlying them, that put wind in the sails of a raccoon's existence. And a mouse's. And a pigeon's.
Spicy foods and bathing ravens
Our own lives offer many ways to appreciate the evolution/experience dichotomy. If someone asks: 'What is the purpose of your life?,' you're unlikely to answer 'To maximize my reproductive output,' or 'I most want to ensure the propagation of my genes into the next generation.' You are more apt to say, 'I wish to lead a good life,' 'I seek to make the world a better place,' or 'I want to be happy and successful.' And by 'successful,' you are probably referring to how much you enjoy your life. As Aristotle had it: 'Life and pleasure ... are not separable; for without behavior there is no pleasure, and pleasure improves behavior.' Reproduction may be the currency of evolutionary success, but happiness is the currency of individual success. All that matters as far as evolution is concerned is that we survive long enough to reproduce. Individually, we seek a fulfilling, rewarding life, and plan to keep enjoying it long beyond our working years.
I doubt that many animals dwell on their 'careers'; they certainly don't set up retirement accounts. Nor are they likely to muse about maximizing their genetic output. They live – I suspect – mainly in the present, their actions motivated by desires, fears, instincts, and past experiences.
The use of spices in food provides a useful human illustration of the expeirential and evolutionary planes of existence. Scientists, in their quest for ultimate causation, have proposed several explanations for the evolutionary benefits of spicing food. Take your pick:
* spices provide micronutrients
* spices mask the bad taste of partially spoiled foods
* spices help cool us by making us sweat more
* spices combat harmful germs and microbes
Give yourself a point if you chose number four. Evidence currently supports the hypothesis that the antibacterial properties of spices account for our culinary habits, though any number of the above theories may work simultaneously.
Yet when you bite into a burrito are you thinking about banishing bacteria, mitigating malnutrition, dissipating distastefulness or, heaven forbid, swimming in sweat? No, you're enhancing the palatability of your food. Spices make food taste good. They promote pleasure. This is the proximate, experiential reason that we reach for the oregano or the curry powder. Our behavior may be beneficial, and it probably originates in our genes, but it is guided by our experience, by our senses, our desires and preferences. Pleasure rewards adaptive behavior. It is a vehicle by which nature promotes evolutionary success. Pleasure is one of the blessings of adaptation.
A captive iguana stays on her perch beneath a warm sun-lamp rather than venturing into a colder region of her enclosure to retrieve a bit of food placed there. Shall we resort to some calculus of energetics and assume that the survival value of staying on the perch exceeds the survival value of getting the food? Or shall we just conclude that the iguana was so enjoying the warmth that it wasn't worth fetching the grub until hunger got the upper hand? University of Tennessee ethologist Gordon Burghardt, who made this observation, favors the latter interpretation, though he recognizes that staying put may be both the more pleasurable and the more adaptive decision on the part of the lizard (see Chapter 5 for a more hedonistic twist to the experiment.) Indeed, if natural selection favors behaviors that sustain life, then it should also favor rewards – such as pleasurable feelings – that reinforce those behaviors. Pleasure is adaptive, or as Canadian physiologist Michel Cabanac says it: 'pleasant is useful.'
Pleasure helps animals maintain a stable state. When we are cold, we seek warmth and it feels good. When we are hot, that same warmth no longer feels nice and we seek a cooler spot. When we're hungry, we eat and it tastes delicious. When we are full, we stop (usually). We know this from our experience, and from experiments. When human subjects are asked to dip their hand in a container of cool or cold water, they report the experience as pleasant if they are feeling hot (e.g. after emerging from a sauna), and unpleasant if they are feeling cold (e.g. after emerging from a freezer). The same phenomenon (Cabanac calls it 'alliesthesia' from the Greek: 'other-perception') applies to tastes (pleasant when hungry, unpleasant when full), though not to sounds and lights.
Alliesthesia applies to other animals. Nature rewards a cold animal who finds warmth, and vice versa. All an animal needs for alliesthesia to work is the capacity to experience surroundings as pleasant or unpleasant, and to move to a preferred environment. Sensory pleasure induces behaviors that improve homeostasis.
Here's another illustration of the dichotomy between evolution and experience. Many birds bathe – dipping their bodies, flapping their wings and shaking their feathers while standing in shallow water. American biologist Bernd Heinrich, working in the Maine woods, has compiled many observations of ravens bathing, and he acknowledges several possible ultimate, adaptive bases for this behavior. These include hygiene, combating skin parasites, and thermoregulation (maintaining a stable body temperature). But when a raven bathes, she is surely not aware of any evolutionary benefits. She is probably responding to a desire to get wet and cool, just as we enjoy the feeling of cool water or air on our skin when we are sweltering, or slipping into a hot tub on a wintry day.
So, while Darwinian evolution and survival undoubtedly influence animals' actions, animals aren't responding consciously to these influences. Yet it does seem that they are behaving according to their moods, their desires, and perhaps even a pre-planned daily schedule. Heinrich concludes that they do it simply because it feels good.
Pleasure (or reward) can be practical independent of its evolutionary origins. For instance, pleasure may enhance survival by reducing stress. Pleasurable activities stimulate the release of stress-reducing compounds into the body, such as opioids and endorphins. Prolonged stress and distress lower the body's defenses against disease in many animals, just as in humans. So by combating stress, the body's pleasure chemicals reduce vulnerability to any number of diseases and maladies.
A recent theory of feline purring is another variation on the theme of direct survival benefits from pleasure. The theory, proposed by Elizabeth von Muggenthaler of the Fauna Communication Research Institute in North Carolina, holds that a cat's purr has mechanical healing properties that speed up the repair of broken bones and other damaged tissues. Several cat species purr, including pumas, ocelots, servals, cheetahs and caracals, as well as the domestic cat. Purring may be cats' answer to ultrasound therapy in humans, which appears to improve bone growth and density. That purring in cats is believed to display contentment raises the question whether purring evolved first as a healing benefit, then later as a communication signal, or vice versa.
The idea that pleasure might be adaptive is not new. The prominent English animal behaviorist George Romanes in 1884 gave it the following Victorian spin:
Pleasures and pains must have been evolved as the subjective accompaniment of processes which are respectively beneficial or injurious to the organism, and so evolved for the purpose or to the end that the organism should seek the one and shun the other.
Julian Huxley, in his treatise on animal language, also acknowledged the importance of individual experience, and it is a cornerstone of Charles Hartshorne's thesis that birds derive – not just deliver – a great deal of pleasure from their songs:
Although the chief function of bird song is to maintain territory, it does not follow that the chief ... emotive meaning of singing for the bird is territorial hostility. ... Evolutionary causes of present behaviour lie deep in the past, but the animal is living now...
Another 20th-century ornithologist, Alexander Skutch, saw more than a struggle for survival in the lives of tanagers, flycatchers, elaenia and jacamars he studied in the New World tropics. He described the singing that accompanies nest building, incubation, and especially fledging of young in these species as 'a triumphant paean for the successful conclusion of their nesting.'
Are these the musings of starry-eyed scientists in moments of levity? Probably. Does that make them wrong? Probably not. The evolutionary importance of pleasure for motivating survival behaviors gives good reason to believe that they are right.
Some basic ingredients for pleasure
For pleasure to aid animals, they need the physical equipment to experience it. That we experience bliss, joy, comfort and satisfaction suggests that some other animals do too, because they are built like us in all the relevant ways. All vertebrates – mammals, birds, reptiles, amphibians and fishes – share the same fundamental body plan: a bony skeleton that supports a muscular system which enables the animal to move about, a nervous system that shuttles signals to different parts of the body and whose center of operations is the brain, a circulatory system that transports oxygen and other nutrients to body tissues, digestive and excretory systems that process food and eliminate wastes, a hormone system that helps regulate body processes, and a reproductive system evolved to ensure propagation.
To this shared foundation we can include a sensory system. All vertebrates have the same five basic senses as us: sight, smell, hearing, touch, and taste. There are some rare exceptions, such as the cave- dwelling fishes and salamanders that have gradually lost the capacity for vision, having lived for many generations in permanently dark environments. The senses are the interface between an animal's nervous system and its surroundings. The abilities to detect and avoid unpleasant stimuli and to seek rewards are the raw materials on which natural selection can act to favor pleasure and pain.
With all this equipment in common, it is no surprise that humans and animals share much of the same physiological and biochemical responses to sensory events. When we experience something painful or pleasurable, our brains signal our glands to secrete chemicals to help us deal with the situation. Human emotions are linked to two brain structures, the amygdala and the hypothalamus, and mediated by biochemicals including dopamine, serotonin and oxytocin. Many animals, especially mammals, possess these same neurological structures and brain chemicals as we do. That needn't necessarily mean they share our feelings, but careful observation of animals in action suggests that they do.
Recent brain imaging technologies such as PET and MRI provide further evidence that animals experience emotions somewhat like we do. There are, for example, remarkable similarities in brain regions in guinea pigs experiencing parent–offspring separation distress and in human brains during feelings of sadness. It is known that a variety of discrete emotional–behavioral control systems inhabit the same distinct regions of the brains of all mammals. According to American neuroscientist Jaak Panksepp, the core emotions – fear, rage, panic, play, seeking and lust – arise from the deep recesses of our primitive brains, and are believed to have evolved long before consciousness.
The brain releases dopamine in response to rewards like sex, food and water. The ability to produce dopamine has probably existed in animals for hundreds of millions of years. Even the humble sea pansy, a jellyfish relative, produces it, though probably not in relation to pleasure and pain. Goldfish prefer to swim in places where they have received amphetamine, which stimulates dopamine release from their brains. Such pleasure-promoting drugs as dopamine have probably played an important role in the evolution and maintenance of survival behaviors, at least in vertebrates.
Opiate receptors in human brains allow us to perceive pleasurable stimuli such as sweet tastes. Panksepp has shown that when rats play, their brains release large amounts of dopamine and opiates. When both humans and rats are given drugs that block these receptors, they rate the sweetness of normally 'liked' foods as less pleasant than normal.
Kent Berridge at the University of Michigan has devoted much of his career to the study of pleasure in the animal brain. Working mainly with taste in rats, Berridge's work suggests that brain networks cause 'liking' reactions to certain things in the animal's environment. These reactions suggest the conscious experience of pleasure (although in his view, pleasurable experience does not require consciousness). The crucial feature of positive states, he argues, is that potentially pleasurable events (e.g. the taste of sugar) be accompanied by positive patterns of behavior (e.g. licking of the lips).
Animals' brains appear to respond to many types of sensory pleasure, including food pleasure, drug pleasure and sex pleasure. More abstract forms of pleasure – including social joy, love, intellectual pleasures, aesthetic appreciation and even morality – are still largely unexplored, but as we shall see, interest in these is stirring.
A window on pleasure
Endowed with the brains, senses and biochemistry for responding to both rewarding and punishing stimuli, animals might be expected to behave accordingly. Because behavior is more readily observable than other aspects of a living animal (such as its biochemistry and physiology), it provides a practical – albeit imperfect – glimpse of their experiences. If other animals can experience pleasure, then we might reasonably expect them to behave in ways suggestive of pleasure in the sorts of situations that humans find pleasurable. The postures and expressions of domestic dogs and cats, for example, when receiving caresses from a trusted human, hint that they respond to the pleasure of touch something like we do – perhaps more so. That dogs and cats actively solicit more rubs or strokes bolsters the idea that they derive something beneficial from the stimulation.
A growing number of studies of wild animal populations, some spanning many years, even decades, are revealing nuances of animal lives that cursory studies miss. Chimpanzees, we now know, fashion tools and share food, and different populations have different cultural practices. African elephants communicate over distances of several kilometers using infrasound calls. Hyena societies are matriarchal and defend finely demarcated clan boundaries. Albatrosses mate for life and live for 70 years or more. Orca populations have language dialects. Honeyguides (a tropical bird) cooperate with honey-badgers and humans to get honey. And reef fish line up for 'cleaner' fishes to remove parasites and debris from their skin and inside their mouths and gills.
For many reasons, including their social intelligence and easygoing nature, rats are much studied, especially in the laboratory. They, too, show the behavioral hallmarks of pleasure. Studies by Panksepp and colleagues show that rats solicit tickles and strokes from trusted humans while making ultrasonic squeaks in the 50 kHz range (the upper limit of humans is around 20 kHz), just as they do when seeking sex and other rewarding social encounters such as rough-and-tumble play. Rats also become very active when placed alone in a Plexiglas chamber where they have been accustomed to playing with another rat. They vocalize and pace back and forth with excitement, in anticipation of play (see Chapter 4 for more about rat play). (Continues...)
Excerpted from Pleasurable Kingdom by Jonathan Balcombe. Copyright © 2006 Jonathan Balcombe. Excerpted by permission of Macmillan.
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