HAPPINESS: What studies on twins show us about nature --- Part 1

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Written by Ian E. Macindoe

Review of

HAPPINESS: What studies on twins show us about nature,

nurture, and the happiness set-point

by

David Lykken

[Golden Books, 1999; ISBN 1-58238-004-x]

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 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 & 3 (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.

Ian Macindoe