the text refers to a stunning finding from studies of hundreds of adoptive families. what was it?

Abstract

Dr. Irving I. Gottesman was very creative in applying twin research designs to test hypotheses and predictions virtually human behavior. Two designs stand out among others: twins reared autonomously from birth and the twin-family study. I (NS) was inspired to incorporate both of these approaches into my own research programs at California State University, Fullerton. Gottesman's involvement and contributions to reared-apart twin research are described, followed by selected findings from the Minnesota Study of Twins Reared Autonomously (MISTRA), the Fullerton Study of Chinese Twins Reared Apart (CTA), a case written report on separated monozygotic (MZ) female twins from South Korea, and doubly exchanged MZ male twin pairs from Colombia, South America. Recent findings from an ongoing twin-family study of social closeness, and future directions, are also presented.

Twins reared autonomously from nascence are a rare unplanned experiment, assuasive unique insights into genetic and environmental factors underlying human behavior. Such studies are an informative variation of the classic monozygotic (MZ)–dizygotic (DZ) twin comparison. That is because similarities betwixt reared-together twins may reflect both shared genes and shared environments, whereas similarities between reared-apart twins offer direct estimates of genetic influence (Segal, Reference Segal2012). The origins, methods, findings, and implications from iv major reared-apart twin studies are available in comprehensive volumes published when these studies concluded (Juel-Nielsen, Reference Juel-Nielsen1965; Reference Juel-Nielsen1980; Newman et al., Reference Newman, Freeman and Holzinger1937; Segal, Reference Segal2012; Shields, Reference Shields1962). Results from other reared-apart twin projects have as well been reported in the scientific literature (meet, eastward.g., Kendler et al., Reference Kendler, Thornton and Pedersen2000; Zhou et al., Reference Zhou, Gao, Lv, Yu, Wang, Liao and Wang2015). Gottesman was intensely interested in the research possibilities offered past reared-apart twins and fabricated pregnant contributions in this regard.

Accidentally exchanged twins are a rare subgroup of separated twins, with merely nine documented cases world-wide. The complete chronology of these pairs is summarized in Table i. Of particular interest is the most recent example involving a double exchange betwixt 2 pairs of MZ male twins from Colombia, Due south America. This upshot generated a series of genetically and environmentally informative kinships, some familiar, but some unique. Familiar sibling sets are two reared-autonomously MZ (MZA) twin pairs raised in dramatically unlike environments. The unique sibling pairs include: (a) two virtual twin pairs (same-historic period unrelated siblings) who believed they were DZ twins and were raised as such; and (b) two pairs of 'replicas' (unrelated siblings who were not reared together, but who genetically replicated the unrelated reared-together pairs); comparing replicas with virtual twins yields a measure out of shared ecology influence. Gottesman was fascinated past this situation and was instrumental in making some Spanish protocols available equally I (NS) prepared to visit Colombia to study these twins. A book detailing the life histories, physical evolution, and behavioral traits of these twins, Accidental Brothers, was dedicated to Irv (Segal & Montoya, Reference Segal and Montoya2018).

TABLE i Chronology of Switched-at-Nascence Twin Pairs

Twins Reared Autonomously

In his 1980 introduction to Juel-Nielsen'southward Danish reared-apart twin study, Gottesman wrote, 'Amidst the furor created (Hearnshaw, Reference Hearnshaw1979) past [Sir Cyril Burt'southward] fabrication of data, co-workers, and pairs of twins three genuinely archetype studies of such rare pairs comprising much more than mere disembodied test scores for IQ have been ignored' (p. 7). His recognition of the investigatory power of reared-autonomously twins is further evident in his subsequent remarks, also in the introduction: 'Identical twins brought up apart are scarce, indeed, and their potential for stimulating enquiry ideas almost the origins of normal and abnormal characteristics is great' (p. 9). He shared these views with his close colleague James Shields, who conducted the second reared-apart twin study in Great britain in 1962. 'I doubt if MZAs will e'er be more numerous and representative plenty to provide the main prove about environment, or nigh genetics, but they furnish critical examples of persons of identical genotype reared in different homes. They can give unique existent-life illustrations of some of the many possible pathways from genes to human being beliefs — and then will always be of homo and scientific interest' (Shields, Reference Shields1978, p. 92).

Gottesman was a kinesthesia fellow member at the University of Minnesota in 1979 when Dr. Thomas J. Bouchard, Jr. invited newly reunited MZA twins, Jim Lewis and Jim Springer, to his laboratory for several days of intensive psychological and medical assessment. The thought of a reared-autonomously twin study had been in the air prior to the discovery of the 'Jim twins', just Bouchard was not optimistic about identifying a sufficiently large sample of separated sets. Withal, the media attending surrounding the Jim twins attracted other participants, and when the study concluded in 1999, a full of 137 pairs (81 MZA and 56 DZA) had been assessed (Segal, Reference Segal2012).

Gottesman was closely involved with this study despite his absenteeism from Minnesota during the years 1980–2001. He co-authored papers on personality (Markon et al., Reference Markon, Krueger, Bouchard and Gottesman2002), intelligence (Johnson et al., Reference Johnson, Bouchard, Krueger, McGue and Gottesman2004), and twin methodology (Johnson et al., Reference Johnson, Turkheimer, Gottesman and Bouchard2009), but his signature contributions are two papers on the Minnesota Multiphasic Personality Inventory (MMPI) scales (DiLalla et al., Reference DiLalla, Carey, Gottesman and Bouchard1996; Reference DiLalla, Gottesman, Carey and Bouchard1999). The senior author on both MMPI papers was David DiLalla, Gottesman's former doctoral student and a contributor to this symposium; co-author Gregory Carey was also one of Gottesman'southward former students.

Like Gottesman, I (NS) was closely involved with the Minnesota Report of Twins Reared Autonomously (MISTRA) as a postdoctoral fellow (1982–1985) and research associate (1985–1991), every bit well every bit in the years that followed. In 2006, I launched the showtime prospective study of reared-autonomously twins adopted from China and completed several case reports of twins raised in different families.

The Fullerton Report of Chinese Twins Reared Apart came nearly in response to a Canadian mother who had adopted 1 MZ female twin from China and wrote to me in 2001 for information about raising a 'singleton twin'. In fact, Communist china'due south i-kid policy, enacted in 1979, led to the abandonment of hundreds of thousands of female infants; that policy and the cultural preference for male children are indirectly responsible for separating twins, more often than not female (Segal, Reference Segal2005; Segal et al., Reference Segal, Stohs and Evans2011). I have assessed 23 separated sets (21 from Prc and ii from Vietnam) and completed follow-up visits for approximately half the sample. The twins' hateful historic period at their first assessment was nine.60 years (SD = half dozen.48), and ranged between 3.19 and 24.98 years. Twins completed a general intelligence test, and their parents completed forms concerning their child'southward behavioral problems, medical life histories, family groundwork, and other areas. Companion studies of adopted Chinese twins raised together (CTTs) and virtual twins (VTs; same-age unrelated children of all backgrounds raised together from birth) are also in progress.

Two papers from this ongoing research program concern twin relationships and developmental risks. A qualitative analysis of the Chinese twins' responses to their first meeting with, and first departure from, their co-twin found that twins older than 18 months of age displayed potent attraction toward one another, whereas younger twins showed more neutral reactions. Older twins likewise showed more than intense reactions and greater upset than younger twins at the time of departure (Segal & Marelich, Reference Segal and Marelich2011). This exploratory story included only the first 10 pairs; a more in-depth assay of the twins' social relationships is planned for the future. A second study combined CTTs and VTs in a study of developmental risks. Surprisingly, age at adoption added less than other predictors to adoptees' externalizing and internalizing behaviors. Family factors, such as parental didactics, contributed significantly to the behavioral outcomes of the CTTs. Comparing the resemblance of CTTs and VTs showed that genetic influence affected initial adaptation to adoption, refusal/abstention, cying/clinging, and developmental delays (r _is = 0.71–0.91), with shared environmental effects evident for the latter two measures (Segal, Tan et al., Reference Segal, Tan and Graham2015).

I (NS) accept completed four case reports of reared-apart twins, iii MZAf pairs born in South Korea (Segal & Cortez, Reference Segal and Cortez2014; Segal & Hur, Reference Segal and Hur2008; Segal, Hur et al., Reference Segal, Hur and Graham2015) and ane DZAf pair built-in in England (Segal, Cortez et al., Reference Segal, Cortez, Zettel-Watson, Red, Mechanic, Munson and Reed2015). Co-twins in all three MZAf pairs were raised in different countries (two in the United States and South korea, and ane in the United States and France). Despite the extremely different environments in which some of these co-twins were raised, some striking similarities in their behavioral and medical characteristics were observed. At the same time, differences in their mental abilities and personality traits were expressed that were peradventure tied to events in their respective life histories. The co-twins in the DZAf pair both remained in England until 1 of the twins moved to the United states of america in her twenties. These twins, who were reunited at 78 years of historic period, accept been entered into the Guinness World Records as the world'south longest separated gear up (GWR, 2016). As expected, given their 50% average genetic relatedness, these twins were less akin behaviorally than the member of the 3 MZAf pairs.

In 2012, I authored Built-in Together-Reared Autonomously: The Landmark Minnesota Twin Written report, a book that surveyed the history and findings of the MISTRA (Segal, Reference Segal2012). Gottesman was i of two prepublication reviewers, and on 1 Saturday morning time, he spent several hours on the telephone with me commenting on various sections. I am confident that the book was significantly improved because of his perceptive middle.

Twins Switched at Nascency

Twins switched at birth are identified very rarely, reflected in the fact that only nine cases have been documented worldwide. Nevertheless, I strongly doubtable that some twins are growing up either as singletons in the incorrect family, or as VTs assertive that are DZ. In fact, two independent medical companies estimated that between xx,000–23,000 misplacements of newborns occur each year in United states hospitals, but are chop-chop corrected (Dna Diagnostics Center, 2010; Rusting, Reference Rusting2001). However, given the very big number of potential errors, information technology seems unlikely that all such mistakes are rectified.

MZ twins would have an easier fourth dimension learning if they had been exchanged because of their identical appearance — in fact, instances of mistaken identity were responsible for revealing the truth in all 9 cases. In 2011, I published a book roofing the life events and behavioral similarities and differences of a switched-at-birth MZAf pair from Gran Canaria, Spain (Segal, Reference Segal2011). These twins learned about the switch at age 28 when a family friend was certain that a clothing store customer was a woman she had known for some time.

Two of the ix cases involved a double exchange, that is, the switching of a newborn twin in one pair with a newborn twin in some other pair. The get-go case, which occurred in Puerto Rico, involved an MZAf pair and an allegedly DZAf pair. In this case, the right children were returned to their biological families when they were 18 months quondam. This was traumatic for the mother and begetter who were interviewed, given the stiff parent–child attachments that had adult. However, a more striking case from Republic of colombia, South America came to light in 2014 when it was discovered that a newborn MZAm twin in 1 pair had been exchanged with a newborn MZAm twin in another pair. Again, the truth was revealed because of mistaken identity when the twins turned 25. The post-obit section expands upon selected aspects of these twins' physical and behavioral evolution. All 4 twins are shown in Effigy 1.

Effigy 1 The four Colombian twins at a family gathering in the land, March 2015. The members of one MZA twin pair are the commencement and 2d from the left; the members of the other MZA twin pair are third and quaternary from the left. Photo credit: Dr. Nancy Fifty. Segal.

Zygosity

The monozygosity of both twin pairs was confirmed past concordance across 21short tandem echo markers (STRs). However, it was of involvement to utilize Lykken'due south (Reference Lykken1978) zygosity cess formula, based upon fingerprint ridge count and body size; using these numbers, the probability of misclassification is less than 0.1%. Kevin Haroian, who worked closely with Lykken, performed these calculations on data gathered from the twins in 2015 and 2016; the 2015 measures included height, weight, ponderal index and total fingerprint ridge count, while the 2016 measures additionally included the cephalic index and updated weight. The zygosity probabilities for the reared-autonomously twins and reared-together unrelated brothers are summarized in Tables ii and iii.

Tabular array 2 Colombian Twins' Body Size Measures

TABLE 3 Probability of Colombian Brothers' MZ Twinship Based on Fingerprint Ridge Count and Ponderal and Cephalic Indices in 2015 and 2016

Several findings are worth noting: First, Table 2 shows that one twin (Country-i) gained over xx pounds (nearly 10 kg) since the commencement visit (approximately 15 months earlier), increasing his BMI from 23.04 to 26.49 and widening the departure between himself and his co-twin. (His weight proceeds was due to intense working out at a gym and a dietary regimen of high protein drinks.) Nigh importantly, Table 3 shows that increasing the number of genetically informative traits in Lykken's formula mostly increases the probability (and presumed accuracy) of twin-type classification. Nevertheless, it also shows that the 1 twin's weight gain caused a substantial drop in the probability that he and his co-twin are MZ twins (87 to 47%). Thus, the timing of such assessments tin can be disquisitional — it is likely that the twins would have been diagnosed every bit DZ by the rules specified in Nichols and Bibro'southward (Reference Nichols and Bilbro1966) concrete resemblance questionnaire, a weight divergence of 15 pounds or more is one alphabetize of dizygosity at the second level of certainty. Given the foregoing, the best method for zygosity diagnosis remains Dna analysis.

Cognitive Evolution

The twins completed both the WAIS-IV IQ test and the Raven Advanced Progressive Matrices (APM), Set-Ii (Raven, Reference Raven1965). In the interest of confidentiality, general intelligence test results were summarized in full general terms by Segal and Montoya (Reference Segal and Montoya2018). In cursory, the city-raised twins outscored their country-raised co-twins, (who had non avant-garde beyond the 5th grade), with both similarities and differences noted in the profiles of the reared-autonomously twins and unrelated pairs. One set of replicas performed quite differently, while the other ready showed unexpected resemblance in their contour design, although non in their level. These findings are of interest given the different life histories of the various pair members, but this single instance does not claiming the l–75% genetic influence on full general intelligence, based upon years of twin and family inquiry.

The Raven APM, Prepare II is a non-verbal multiple-pick test, devised in 1947 for officer selection. Information technology assesses the power to draw comparisons betwixt figures and to develop a logical method of reasoning. The 36 items can exist completed either with a fourth dimension limit (capacity for ascertainment and clear thinking) or without a time limit (efficiency of intellectual work). The twins completed merely Gear up-Two as a ability exam, without a fourth dimension constraint, in order to reveal differences in what they knew and could do. Efforts were made to note the particular on which they were working at 42 min, given that approximately forty min yields a satisfactory score distribution in group administrations. Instructions were reviewed carefully prior to testing.

The amend educated city-raised twins outscored their country-raised co-twins. The co-twins in one MZA pair were at items 34 and 24, respectively, later on 42 min had elapsed, whereas the co-twins in the other pair completed the exam in less than 42 min. Members of the unrelated pairs (VTs) scored closer to one another than to their reared-apart co-twins. Interestingly, the degree of difference betwixt the two MZA pairs and the ii VT pairs was about the same. The biggest difference among the six pairings was between i of the replicated pairs, followed by the 2 MZA twin pairs. These findings are shown graphically in Figure 2.

FIGURE ii Colombian twins' functioning on the Raven APM, Set Two. Illustration credit: Kelly Donovan, BA.

These results suggest that the twins' different educational backgrounds played a role in their performance, with the lack of pedagogy overwhelming the genetic potentials of the country-raised twins, and despite the general recognition of the Raven APM as a valid, non-verbal measure of mostly fluid intelligence (Kvist & Gustafsson, Reference Kvist and Gustafsson2008). General intelligence examination scores for some twins in the MISTRA varied as a function of educational experience, but the effects were not systematic (Segal, Reference Segal2012). In addition, Newman et al. (Reference Newman, Freeman and Holzinger1937) establish that educationally advantaged twins generally outperformed their less advantaged co-twins, just the intraclass correlations for both mental ability tests in that study remained high. The lower scores of the country-raised Colombian twins may partly reflect their lack of education, although every bit yet unknown factors (e.thousand., unfamiliarity with the exam state of affairs) may have played a role; the higher scoring state-raised twin had, in fact, obtained a GED in his early twenties. Interestingly, both big Raven and WAIS-Iv discrepancies were noted for ane reared-autonomously pair, whereas simply a large Raven discrepancy was noted for the other pair.

Twin-Family Study of Social Closeness

On a different twin-related track, Gottesman applied the twin-family blueprint to assess the risk of schizophrenia to the children of discordant MZ and DZ twin pairs (Gottesman & Bertelsen, Reference Gottesman and Bertelsen1989). As I noted in the introduction to this special issue (and as Christensen and Bertelesen describe in their article), a cardinal finding was that the offspring of discordant MZ twins were at equal risk for developing the disorder, whereas the offspring built-in only to affected DZ co-twins were at risk. The twin-family study (variously known as the MZ Half-Sibling Design, Nuclear Family Twin Blueprint, Children-of-Twins Approach, and Twin-Pedigree Study) has been used to assess factors affecting a range of physical and behavioral traits, such as cognition (Van Leeuwen et al., Reference Van Leeuwen, Van Den Berg and Boomsma2008), age at menarche (Mendle et al., Reference Mendle, Turkheimer, D'Onofrio, Lynch, Emery, Slutske and Martin2006), externalizing disorders (Hicks et al., Reference Hicks, Krueger, Iacono, McGue and Patrick2004), and self-esteem (Bleidorn et al., Reference Bleidorn, Hufer, Kandler, Hopwood and Riemann2018). My laboratory continues to use this model to compare the social closeness of MZ and DZ twin aunts and uncles expressed toward their nieces and nephews (Segal et al., Reference Segal, Seghers, Marelich, Mechanic and Castillo2007; Segal & Marelich, Reference Segal and Marelich2011). Updated findings and future directions for this project have also been presented (Segal et al., Reference Segal, Mollova, Marelich and Preston2016).

Participants from both intact and non-intact twin pairs (n = 470 individuals: 44 MZm, 318 MZf, fifteen DZm, 93 DZf; 6 male and 28 female twins were from opposite-sex twin pairs) completed a Social Closeness Survey, mostly online, although a minority of participants from the almanac Twins Days Festival in Twinsburg, Ohio completed a pencil and paper version. Two major hypotheses, guided by evolutionary reasoning, were assessed: (ane) MZ twin aunts/uncles will indicate greater social closeness toward their nieces and nephews than DZ twin aunts/uncles, and (two) twins with female co-twins will express greater social closeness toward their nieces and nephews than twins with male co-twins. Hypothesis 1 is derived from Hamilton's (Reference Hamilton1964) assertion that natural pick favors alleles predisposing individuals to act in ways that favor transmission of those alleles. Alleles predisposing individuals to behave altruistically toward others likely to carry copies of those alleles would exist an indirect manner of transmitting one'south genes to future generations, thereby enhancing one'south reproductive success (inclusive fettle). Hypothesis 2 drew upon the concept of paternity uncertainty, namely that considering of hidden ovulation, internal fertilization and continuous female person sexual receptivity, males cannot be certain that children delivered by their partner are truly theirs. Thus, greater social closeness should be expressed by uncles and aunts whose nieces and nephews were born to twin sisters, rather than to twin brothers.

Both hypotheses were supported by the data. The principal upshot for zygosity was significant, F(ane, 466) = 10.85, p = .001, with lower scores reflecting increased social closeness. Closeness toward nieces and nephews was greater for MZ twins (M = 22.26, SD = half-dozen.00) than for DZ twins (M = 25.81, SD = 6.02).In add-on, the chief effect for co-twin sexual activity was significant, F(one, 466) = 17.26, p < .001. As expected, closeness was greater for twins with female co-twins (Yard = 22.37, SD = 5.09) than for twins with male person co-twins (M = 26.45, SD = five.47). Non surprisingly, social closeness correlated significantly with perceived similarity: r = 0.58, p < .001. This study is ongoing and can exist completed online at https://fullerton.qualtrics.com/jfe/form/SV_1XJDEwEaPIYEiyN.

Acknowledgment

Irving I. Gottesman may be gone, but he is not forgotten. His retentiveness remains in the minds of everyone who knew him, and his work will be cited oftentimes in the years to come.

I wish to thank the members of this panel for their participation and their generosity. I also wish to thank Irv's University of Minnesota colleague, Dr. Bruce Overmeier, for launching an 'In Honor Of' page for Irv, sponsored by the Federation of Associations in Behavioral and Encephalon Sciences (FABBS). Colleagues, friends, and people who may have known Irv simply by his work are asked to consider making a donation of whatever size — all donations are welcome. Delight visit http://fabbs.org/our_scientists/irving-i-gottesman-phd/

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