BOOK REVIEW No Two Alike: Human Nature and Human Individuality Judith Rich Harris (2006).W.W. Norton & Company, 322 pp, $US26.95, ISBN 0393059480. they cannot explain differences variety of research fields, develop- We are all social beings by nature. between genetically identical indi- mental, cognitive, social, and That is what united the human viduals (i.e., monozygotic twins). evolutionary psychology, neuro- species in our successful trip Similarly, gene–environment correla- physiology, primatology, and even through evolution. But it is also the tions concern the way different entomology. Step by step she clue to explain human individuality, genotypes drive people to different builds upon her ‘group socializa- states Judith R. Harris in her environments. Harris shows how a tion theory’ outlined in The second book, No Two Alike. After second critical look at apparently Nurture Assumption. She departs her first very successful book, The appealing research can reveal hidden from the idea that behavioral con- Nurture Assumption (1998), Harris methodological deficiencies that lead sistencies are driven by genes, in her second book sets out to dis- one to question the results. This is whereas the adaptive plasticity of entangle how two genetically the case with Suomi’s studies on behavior is driven by our ability to identical individuals who grow up cross-fostered monkeys, which discriminate across different envi- in the same family, can turn out dif- claimed to demonstrate that nurtur- ronments, and react differentially ferently. How is it possible that they ing mothers prevent their children to them. This, translated into are perceived by themselves and by from becoming aggressive. behavioral genetics terms, implies others as perfectly unique personal- Harris applies the same kind that the nonshared environment is ities? Harris takes the mask off the of skepticism to Frank Sulloway’s responsible for the majority of per- behavior geneticists’ so-called ‘non- publications concerning the effects sonality changes that occur shared environment’. of birth order on personality dif- throughout the lifespan. In the first half of the book, ferences among siblings. Sulloway In the specification of the Harris offers an impressive review explained the differences between mechanisms that explain human of theories and evidence presented siblings as due to competition for individuality, Harris recovers the by developmental psychology, resources within the home envi- modular conception of the mind behavioral genetics and evolution- ronment. The ease with which his from evolutionary psychologists ary psychology, to explain theories spread through the scien- such as Steven Pinker, Leda nongenetic differences in personal- tific community and general Cosmides and John Tooby. She ity. Harris proposes that children’s public is related to the intuitive proposes that mental modules, personality is probably shaped as character of his claims. However, similar to the ones that control ‘plastic’ by evolutionary processes, he insists on concealing his ‘evi- vision or language, lead the two so that they are able to adapt their dence’. Data from behavior main social processes: socialization behavior to circumstances in adult genetic studies show that differ- and personality development. The life. Although biological and envi- ences in parental behavior are a human species, as social beings, ronmental noise may cause some of response to, and not a cause of, experiences two confronting ten- the changes, the author insists that differences between siblings. dencies: being accepted members ‘randomness is the explanation, or The first part of the book will of a group, and differentiating the excuse, that a scientist resorts to fascinate readers of Twin oneself from other members of the when all else fails’ (p. 49). Research and Human Genetics. group. The socialization system Harris presents several ‘red her- Harris offers an excellent exhibi- drives the first tendency. Children rings’ that have been proposed as tion of complex reasoning and observe the different behavior of explanations for nongenetic person- provides a comprehensive review people who belong to different ality differences. Gene–environment of the literature, while making it social categories (e.g., males and interaction is the first. Although understandable and enjoyable for females, adults and children). gene–environment interactions are the general public. Their task in becoming socialized relevant in understanding how In the second half of her book is to learn to which social cate- genetically different people react dif- Harris distils an overwhelming gories they belong, and in which ferently to the same circumstances, amount of evidence from a great situations those categories apply. Twin Research and Human Genetics Volume 9 Number 5 pp. 703–704 703 Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.126, on 25 Sep 2021 at 22:50:43, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1375/twin.9.5.703 Book Review The relationship system drives our opmental noise or random events), are possible for the personality dif- need to communicate and relate to will be amplified by the feedback ferences between monozygotic other people. It stores information that they receive from other twins. Epigenetic differences or the on each specific individual, and is people’s reactions. moderation of genetic expression responsible for our ability to make The readers of Twin Research by other environmental factors fine distinctions among them. and Human Genetics may seem promising possibilities. Personality development, and approach the second part with Yet again, Harris’ writing is therefore human individuality, is reservations. As the author says both inspiring and stimulating. driven by the interaction between herself, scientists tend to specialize With her ability to highlight the the relationship system and the in a specific field of research and best and worst in every scientific status system. The status system always view evidence through the work and her sharp style of rea- drives our innate need to differ same ‘glasses’. Harris’s theory is soning and communicating, she from others, to ‘compete’, to stand complex as it incorporates ele- provides the reader with unex- out as unique individuals within ments from a wide range of pected views of the problem. No our group, or social category. We research fields. As with any Two Alike will provoke less con- learn how to accomplish this goal complex theory, it not only troversy than The Nurture Assumption, but will surely be the by ‘reading’ what other people appears hard to understand, but source of inspiration for new and store in their relationship system also difficult to test. But this does creative research initiatives. about us. Even genetically identical not mean impossible! In the last twins are identified by others as chapter of the book, the author Irene Rebollo different unique individuals, and proposes how certain features of Department of Biological Psychology, the slightest difference between the theory may be tested. There is Vrije Universiteit, Amsterdam, them (due, for example, to devel- no doubt that other explanations the Netherlands 704 Twin Research and Human Genetics October 2006 Downloaded from https://www.cambridge.org/core. IP address: 170.106.202.126, on 25 Sep 2021 at 22:50:43, subject to the Cambridge Core terms of use, available at https://www.cambridge.org/core/terms. https://doi.org/10.1375/twin.9.5.703.