Hockenbury Discovering Psychology 5th txtbk

444 CHAPTER 10 PersonalityIN FOCUSExplaining Those Amazing Identical-Twin SimilaritiesAs part of the ongoing Minnesota Study of Twins Reared Apartat the University of Minnesota, researchers David Lykken,Thomas Bouchard, and other psychologists have been studyinga very unusual group of people: over 100 pairs of identical andfraternal twins who were separated at birth or in early childhoodand raised in different homes. Shortly after the study began in1980, the researchers were struck by some of the amazing similaritiesbetween identical twins (Lykken & others, 1992). Despitehaving been separated for most of their lives, many twins hadsimilar personality traits, occupations, hobbies, and habits.One of the most famous cases is that of the “Jim twins,” whohad been separated for close to 40 years. Like many of the otherreunited twins, the two Jims had similar heights, postures, andvoice and speech patterns. More strikingly, both Jims had marriedand divorced women named Linda, and then marriedwomen named Betty. One Jim named his son James Allan, whilethe other Jim named his son James Alan. Both Jims bit their nails,chain-smoked Salems, and enjoyed working in their basementworkshops. And both Jims had vacationed at the same Floridabeach, driving there in the same model Chevrolet (Lykken &others, 1992).Granted, such similarities could simply be due to coincidence.Linda, Betty, James, and Alan are not exactly rare names in theUnited States. And literally thousands of people buy the samemodel car every year, just as thousands of people vacation inFlorida. Besides, if you look closely at any two people of thesame age, sex, and culture, there are bound to be similarities.It’s probably a safe bet, for example, to say that most collegestudents enjoy eating pizza and often wear jeans and T-shirts.But it’s difficult to dismiss as mere coincidences all the strikingsimilarities between identical twins in the Minnesota study.Lykken and his colleagues (1992) have pointed out numerousquirky similarities that occurred in the identical twins they studiedbut did not occur in the fraternal-twin pairs. For example, inthe entire sample of twins, there wereonly two subjects who had been marriedfive times; two subjects who habituallywore seven rings; and two who left lovenotes around the house for their wives. Ineach case, the two were identical twins.And only two subjects independently(and correctly) diagnosed a problem withresearcher Bouchard’s car—a faulty wheelbearing. Again, the two were membersof an identical-twin pair. While Lykkenand his colleagues acknowledge thatsome identical-twin similarities are probablydue to coincidence, such as the Jimtwins marrying women with the samefirst names, others are probably geneticallyinfluenced.So does this mean that there’s a genefor getting married five times or wearingseven rings? Not exactly. Although somephysical characteristics and diseases are influenced by a singlegene, complex psychological characteristics, such as your personality,are influenced by a large number of genes acting incombination (Caspi & others, 2005; Marcus, 2004). Unlike fraternaltwins and regular siblings, identical twins share the samespecific configuration of interacting genes. Lykken and his colleaguessuggest that many complex psychological traits, includingthe strikingly similar idiosyncrasies of identical twins, mayresult from a unique configuration of interacting genes.Lykken and his colleagues call certain traits emergenic traitsbecause they appear (or emerge) only out of a unique configurationof many interacting genes. Although they are geneticallyinfluenced, emergenic traits do not run in families. To illustratethe idea of emergenic traits, consider the couple of averageintelligence who give birth to an extraordinarily gifted child. Byall predictions, this couple’s offspring should have normal, averageintelligence. But because of the unique configuration of thechild’s genes acting in combination, extraordinary giftednessemerges (Lykken, 2006; Lykken & others, 1992).David Lykken compares emergenic traits to a winning pokerhand. All the members of the family are drawing from the same“deck,” or pool of genes. But one member may come up withthe special configuration of cards that produces a royal flush—the unique combination of genes that produces a Shakespeare,an Einstein, or a Beethoven. History is filled with cases of peoplewith exceptional talents and abilities in varied fields who grewup in average families.Finally, it’s important to point out that there were many differences,as well as similarities, between the identical twins inthe Minnesota study. For example, one twin was prone todepression, while the other was not; one twin was an alcoholic,while the other did not drink. So, even with identical twins, itmust be remembered that personality is only partly determinedby genetics.Heredity or Environment? Along withsharing common genes, many identicaltwins share common interests andtalents—like concert pianists Alvin (left)and Alan Chow. As students at theUniversity of Maryland, they graduatedwith identical straight-A averages—andshared the stage as co-valedictorians.Both studied piano at Juilliard, and todaythey are both music professors with activeperformance schedules. In addition toperforming solo, they frequently performtogether in recital. However, the Chowtwins were reared together, so it wouldbe difficult to determine the relativeimportance of environmental andgenetic influences on their talents andcareer paths.