What studies on twins show us about nature, nurture, and the happiness set point
David Lykken has been associated for much of his distinguished academic life with the Minnesota Twin Registry, the largest known collection of identical and fraternal twins used for psychological research. Studies of twins are crucial in the psychologists' ongoing struggle to determine how much of human nature and behaviour results from an individual's life experience and how much the person's genetic make-up sets the limits within which experience can hold sway.In a study of retirement leisure patterns Peppers (1976) looked at four patterns. They were active-social, active-isolate, sedentary-social, sedentary-isolate. The four most popular activities came from each of the four patterns while the ten most popular activities were isolate activities. An implication of this study is that older people enjoy time alone and perhaps spend much of their activity time alone.
The following review by Ian Macindoe PhD - is a summary of Lykken's research on Happiness: what studies on twins show us about nature, nurture, and the happiness set point.
In Happiness the author examines the evidence from a huge body of research - his own and that of others - that points to the conclusion that 'nearly every psychological trait or tendency that we can measure reliably owes part of its variation from person to person to genetic differences between people' (p. 3); and he discusses how the evidence can be understood in what it reveals about human happiness and wellbeing. The book is central to basic questions surrounding mental health.
The book is divided into six parts and I will deal with each part separately in this review.
Part 1:The Heritability of Happiness provides an introduction to the discipline of evolutionary psychology, and goes on to explain how psychologists can estimate the degree to which individual differences in such traits as irritability and happiness can be attributed to genetic differences between people. It also tackles 'the difficult question … of how it can be that our genes, whose function is to synthesize the production of enzymes and other proteins, can possibly influence, much less determine, complex psychological tendencies or traits' (p. 4).
The detail of the evidence discussed in Part 1 of the book cannot be gone into here, for it is somewhat technical and … well, detailed. I can, however, share some aspects of the author's work that will give you an indication of its worth. At the start of each chapter Lykken provides one or more quotes (often from such favourite writers as Mark Twain) that give the reader a synoptic glimpse of the import of the chapter. So, for example, at the start of Chapter 1 (entitled This Happy Breed) the author quotes a sentence from the work of his colleague Bouchard: 'The genes sing a prehistoric song, that must sometimes be resisted, but which cannot be ignored'. In this chapter Lykken reviews the evidence, both experimental and anecdotal, leading to the conclusion that genetically we each have a typical level of happiness/contentment. This typical level Lykken calls our 'set point' for happiness. So, in the usual course of events, when we may be elated by some success or made sad by some unfortunate experience, we nevertheless tend to return to our own set point of happiness in the medium-to-long term. From an evolutionary point of view most people (given the basic necessities of life) feel reasonably happy most of the time. Ups and downs of mood are familiar to us all, but natural selection has ensured (for the propagation of the species) that generally most people adapt to their circumstances with reserves of optimism and energy that enable humankind to survive. 'Unless we are currently trapped in some desperate, life-threatening situation, especially one that continues on until our reserves of resiliency are totally depleted, it is unlikely that any single event, accomplishment, or stroke of good fortune will produce an enduring increase in our level of subjective wellbeing' (p. 32).
The Minnesota Study of Twins Reared Apart (MISTRA) has a fascinating history, but eventually had 120 pairs of reared-apart twins plus four sets of reared-apart triplets - 'the most extensive and intensive study of these rare experiments of (human) nature ever attempted' (p. 41). In an early report of results (Science 250, 1990, 223-228) it was found that, on most measurable psychological traits, monozygotic twins reared apart (MZA) were as similar as monozygotic twins reared together. Among persons of European ancestry, for psychological features that can be measured, heritabilities range from about 25 per cent to 80 per cent. Or, to put it more concretely, from one-fourth to four-fifths of the variation from person to person in such features as IQ, extroversion, neurotic tendencies, musical talent, creativity, types of interests, religiousness, authoritarianism and happiness, is associated with genetic differences between those persons.
While Lykken's book makes use of these scientific findings, the author himself delights in everyday examples and the book is a fascinating read where literary and folk-tale anecdotes (not to mention the author's own family) are cited to illustrate various points. Even humorous cartoons help: My favourite (on p. 57) shows a man, the owner of the mansion in the background, telling his friend 'I could cry when I think of the years I wasted accumulating money, only to learn that my cheerful disposition is genetic'.
Lykken ends Part 1 of the book with an important qualifier: Happiness as a trait is 'emergenic' which means that it does not run in families, perhaps because it is made up of various component genetic contributions. Each person's happiness set point may be partly determined by the compatibilities between a person's innate tendencies or traits. 'If your innate strengths and weaknesses are compatible with one another, then doing the things that make you happy will come easier than if your various proclivities pull in different directions' (p. 59). Finally, the author stresses that simply because each of us has a happiness set point does not mean that we are unable to influence our own state of happiness. As he puts it we 'can learn to bounce along above our basic set points by learning some new habits, by observing some simple rules …' (p. 60). Parents, for example, need not take a fatalistic attitude to their child rearing, since there is much that they can do to teach their children how to maximise their happiness within some broad limits of their genetic make up.
Part 2: Happiness Makers deals with how our set point level of subjective wellbeing can be affected, for better or worse, by what we do and what we strive for.
Lykken makes a distinction between 'effectance' and 'entertainment'. Effectance is the human motivation to impact the world, particularly in a productive and useful way. Genes for such a capacity are likely to be passed on to later generations, for it is the ancestors who were strong in effectance who were likely to survive, prevail and produce progeny over the centuries. A measure of this human tendency has been developed as the Achievement scale of the Multidimensional Personality Questionnaire. People who score highly on this scale are ambitious, hard working, and set high standards for themselves.
Entertainment, on the other hand, is usually a relief from work, but must be experienced as enjoyable before it can be truly regarded as entertaining. In any case, these two ways of behaving, if applied judiciously in one's life, can assist us in 'bouncing along' above our happiness set point. The analogy of a 'happiness lake' is used to make the concept easier to comprehend: while each of us may have an average depth for our own happiness lakes, largely determined by our brain chemistry that we can do little about, we can exert our own efforts that create waves on which we ride along 'higher than we would if we let our genetic steersman call all the shots'.
Part of the strategy for achieving positive 'waves' is to consciously develop our ability to become 'epicures of experience': to find, develop and enjoy those pastimes that appeal to us (whether that be gardening, carpentry, cooking, moderate use of chemicals such as cocktails, parenting, or countless other constructive avenues). Another important ingredient is to enjoy, or at least feel fulfilled by or satisfied with, one's everyday work.
There is a voluminous body of research showing that the best performance on a complex or creative task, whether in academics or in the workplace, is produced by people motivated by intrinsic interest in the task rather than by contingent rewards (p. 105).
It is important, of course, that the work engaged in should be well within the capacity of the individual who attempts it, otherwise the positive feelings of doing a job well will be overtaken by the frustration and anxiety of grappling with matters for which one is ill equipped. Constructive activity and the exercise of skills are among the most dependable sources of human happiness, says Lykken, and when we are totally absorbed by such activities we may be said to 'be in flow' (that is, to be unselfconsciously focussed, and carrying out a skilled task in which we are fully absorbed; like a concert pianist concentrating on tonality and feeling while the fingers 'automatically' find the correct keys to strike).
Part 3: Happy Families covers parenting, babies, children and pets. Within normal levels of parenting (excluding abuse and neglect) parents may be interchangeable to a large degree without significantly affecting what sort of person any child turns out to be. Children raised together in the same family do not tend to become more alike as they become adults. The way children turn out depends greatly on two sets of factors (and parents are not one of them). The first is genetic makeup; the second is their peer experiences (neighbourhood friends, school buddies, and so on).
Lykken cites the work of Judith Rich Harris as the most persuasive researcher to assert the dominant influence of peer experience. In her book The Nurture Assumption Harris
'manages to relegate to the myths of folk psychology most of what developmental psychologists believe about the importance of parenting. Harris's arguments have compelled me to conclude that, apart from genetic contributions, most parents … have a negligible lasting effect on their children's adult personality and behaviour patterns (p. 118).
Despite this, Lykken tries to show in Part 3 of his book that 'parents can make a real difference' and that 'skilful parents … have happier children than less skilful parents' (p. 118). To begin with, Lykken is probably correct in thinking that most parents would be happier in themselves if they were more skilled in matters of discipline with their children. Since potential childhood candidates for antisocial personalities make up about 25% of children, you and your family are likely to be happier if such outcomes are avoided. It makes sense to think that parents and children who enjoy each other's company over the years will comprise happier households than if there are unhappy relationships. And Lykken presents data from the Minnesota Twin/Family Study to support this supposition (pp. 122-3). Children will be happier (at least while at home) if parents are happier, and vice versa.
A great deal of the chapters on 'happy babies' and 'happy children' revolves around Professor Lykken's accounts of child rearing that he and his wife, Harriet, accomplished in the shepparding of their own three boys through to adulthood. While this makes for entertaining and often insightful story telling, it is light on scientific evidence. However, he does examine the work of others notably that of Gerald Patterson at the Oregon Social Learning Centre, to illustrate the dangers of non-skilful parenting; and this eventually leads to a discussion of unsocialised adults, in particular the psychopathic personality, which is a topic on which Lykken is a leading world exponent. His account of psychopathy and its prevention, and the important distinction to be made from the sociopath, are some of the most telling pages in Lykken's book.
In reviewing this book so far I have summarised the author's argument that, although our general persistent level of happiness - our happiness 'set point' - is determined by our genetic make up, our subjective daily experience of happiness (or feelings of subjective wellbeing) can be influenced by how we conduct ourselves. Part 2 of Professor Lykken's book shows how 'happiness makers' (for example, work and recreational fulfilments) can assist one to keep 'bouncing along' in life above one's happiness set point. Part 3outlined how we can achieve happy families.
The good professor now, in Part 4: Problems of gender, tackles the relationships between the sexes and, while admitting that both women and men may have a similar general recipe for happiness, these recipes differ in their detail. 'Our research with twins has allowed us to discover why couples fall in love and cleave together and also why, too often, they later cleave apart' (p. 172).
The first chapter deals with sex differences, from the finding that female feet are smaller (as a ratio to height) than are men's, through the measured temperamental differences (men are more aggressive and less fearful, women more nurturant and empathetic towards others) to marked differences in leisure-time interests. Some interests, whether occupational or leisure, are substantially different between women and men. The main thing, of course, as far as happiness is concerned, is to vary your interests and to be enthusiastic about experiencing that variety.
Across many cultures men rate youth and beauty high for the attractiveness of females, while women rate males' status as more attractive than good looks. As Lykken says, this makes good evolutionary sense, and also tends to explain why more young women than men suffer from eating disorders where physical attractiveness based on slimness motivates the sufferers' misperception of beauty.
Using a translated questionnaire in sixteen countries Inglehart (1990) found that 80 per cent of both sexes were 'satisfied' with their lives, and 21 per cent of men and 24 per cent of women indicated that they were 'very happy'. And Myers' (1992) research showed that 'working women are neither more nor less contented on the whole than full-time homemakers', it being the challenge and satisfaction of the work that makes the difference, regardless of place of work or remuneration.
The data from twin studies shows that women 'have a stronger need for close, confiding, intimate relationships than does the average man' (p. 182). In general, females score higher on the 'harm-avoidance' scale of the Multidimensional Personality Questionnaire (MPQ) and Lykken acknowledges that this measure of 'fearfulness' is no doubt a mixture of genetic and experiential factors.
Chapter 11, How to stay happy though married, reports research with the Minnesota Twin Registry that helps our understanding of why people fall in and out of love. For many relationships to become lasting ones there is a need for infatuation (romantic love) to keep a couple together long enough for shared experience, mutual understanding and tolerance to develop as the basis on which a long-term partnership can be based. In a cross-cultural study of 58 societies Fisher (1992) found that a modal period of four years occurs prior to a first 'divorce' (whether real or just a considered option) - a period that 'reflects an ancestral strategy to remain pair-bonded at least long enough to raise a single infant through the period of lactation' (p. 191). The Minnesota twin studies suggested, similarly, that 'romantic infatuation … forms an initial bond almost adventiously and then sustains it long enough, in most instances, for an enduring bond to be forged by the slower processes of learning and adaptation that result in companionate love' (p. 196). Who you fall in love with seems not to be determined by your genes, nor your experiences and influences in life, but by your own 'readiness' and the opportunity for a reciprocated romance.
The Minnesota Twin Registry was also used for an investigation of the likelihood of divorce. Divorce among parents or co-twins of monozygotic (identical) twins increased greatly the likelihood that a married twin would divorce. The reasons for this, Lykken explains, is that among these divorced people there are psychological traits that are shared genetically and that are implicated in the failure of a bonded relationship. In the MPQ study it transpired that people high on Social Potency (extraverted, take-charge people) were more at risk of divorce than were introverted people. ' … it is the heritable component of personality that predicts divorce risk' (p. 203). Thus, people who are risk-takers, or are fearless, or are impulsive, are more likely to create friction with their partners. For them, a greater degree of self-control and determination is needed to keep a relationship sustainable.
Part 5: The thieves of happiness covers 'depression', 'fear and shyness' and 'anger and resentment'. The worst thief of happiness, says Lykken, is depression. It is an absence of happiness and, in its worst manifestations, is a life-threatening illness. Susceptibility to depression's two main forms - bipolar affective disorder (in which bouts of depression alternate with manic elation) and primary major depressive disorder - is strongly determined by genetic factors. If one identical twin suffers bouts of either, there is a 40 to 60 per cent chance that the other twin will experience similar bouts. Thankfully, advances in medications now give much hope that, if the right combination of chemicals can be found for a particular person, a great deal of depressive suffering can be alleviated or at least reduced. In 'talking therapies' the challenge is to get depressed persons to genuinely understand that the condition is a temporary imbalance in brain chemistry; that the sad and hopeless feelings, while overwhelming, can lessen with time. Some form of activity, particularly physical exercise of some sort, can often lift the spirits. Dr Lykken, although a mainstream psychologist, suggests that the evidence for the antidepressant effects of the herb, Saint-John's-wort, is such that it should be tried as an alternative, or perhaps a supplement, to more conventional treatments. One of the latter in this day and age is Prozac (fluoxetine hydrochloride), which has helped millions of people during the past decade or so. There is considerable anecdotal evidence that the drug can 'improve' personalities beyond the lifting of morbid depression, which suggests that it might even raise some people's happiness set point. Lykken, however, is of the view that Prozac 'works its wonders not by raising the happiness set point, but rather by disabling a variety of happiness thieves, including depression, shyness, timidity, and unpleasant compulsions … (sufferers) have been freed up to begin making the most of the potential they were born with' (p. 220).
Lykken cites the developmental psychologist, Jerome Kagan, who (like Lykken) was originally 'a radical environmentalist' but who, in the light of the research data, came to realise that 'the power of genes is real but limited'; so that, as Lykken says, 'skillful parenting can mitigate the effects of an excessively shy or inhibited temperament' (p. 222). The other extreme, a relatively fearless child, can be as big a worry to a parent, but for different reasons. A child that fails to fear the consequences of his actions may learn that resisting parental discipline 'pays', that he can get his own way, with the danger that over time he may become unsocialised, possibly even psychopathic. But over-sensitivity to things that can be 'painful', either physically or psychologically, may lead to 'panic anxiety' or similar debilitating inhibitions to normal action. 'Stage fright' is an example discussed by Lykken, and the concept of systematic desensitisation through which many such problems can be solved.
Anger is often a way of overcoming feelings of fear or weakness. People learn that feeling angry feels less distressful than feeling frightened or humiliated. But, of course, feeling happy is more gratifying than feeling angry or resentful. The twins research shows that 'rage-readiness' (a stable component of irritability) has strong genetic influences, although they (like the happiness set point) are 'emergenic' (not running in families). Such genetically predisposed feelings do not have to dominate one's life if one is determined to control such feelings through self-discipline. Most angry flare-ups are those occasions when the 'genes prehistoric song' must be resisted. Similarly, there is little point in constantly blaming one's problems on others (be they parents, teachers, or slings and arrows of outrageous fortune) and carrying permanent resentments like a professional victim. Even if our genes cause us to have our own peculiarities, little constructive is achieved by harping on our misfortune. Everyone is better off if each of us accepts our nature with equanimity and gets on with living as well and contentedly as we can.
Part 6: Happiness among older people is Lykken's appropriate conclusion to his book. Here Lykken is at his 'chatty' best, using examples of colleagues to show that retirement can be one of the happiest and most productive times in life. He also turns to science, however, to observe that happier people last longer than the querulous and dissatisfied. One reason may be that older people feel they have devolved responsibility to a younger group of people, that the state of the world - or one's favourite project or cause - is no longer up to them. But Lykken indicates in his closing pages that older people, particularly those for whom life has been a 'life of the mind', can be equally concerned about what lies ahead for them: how they will die. He makes several wise observations about a rational approach to death and dying, including his own preparation for same; then ends his book with 'I hope to see my grandchildren enter into young adulthood but if not, I hope that at least my own final chapter will be as brief as the one you have just read' (p. 256).
3 December 2003