Thomas J. Bouchard

Twins Reared Together and Apart: What They Tell Us About Human Diversity

The exceedingly close resemblance attributed to twins has been the subject of many novels and plays, and most persons have felt a desire to know upon what basis of truth those works of fiction may rest. But twins have many other claims to attention, one of which will be discussed in the present memoir. It is, that their history affords means of distinguishing between the effects of tendencies received at birth, and of these that were imposed by the circumstances of their after lives; in other words, between the effects of nature and of nurture. (Galton, 1875, p. 4661)

Heritability of fluctuating asymmetry in a human twin sample: the effect of trait aggregation.

Fluctuating asymmetry is thought to reflect developmental instability, which may in turn indicate genetically influenced fitness. Controversy surrounding these claims has centered on the extent to which fluctuating asymmetry is heritable. Most studies have estimated its heritability to be very low using single‐trait measures. This study uses data from a human twin sample to demonstrate that the heritability estimate resulting from the aggregation of fluctuating asymmetry across multiple traits is non‐zero. This is the case even when the estimates of fluctuating asymmetries of the individual traits do not differ significantly from 0. Am. J. Hum. Biol., 2008.

Do environmental similarities explain the similarity in intelligence of identical twins reared apart

Abstract Taylor (1980) claims to show that the similarity in IQ between monozygotic twins reared apart (MZAs) in the three classic studies by Newman, Freeman, and Holzinger (1937), Shields (1962), and Juel-Nielsen (1965) is due to similarity in their environments. A reanalysis, using Taylors classification of the twins into similar and dissimilar environments on the basis of four different criteria, but using the alternate IQ measure used in two of the studies, shows that his findings do not constructively replicate. Taylors conclusion that “it seems reasonable to suggest that the IQ correlations characterizing pairs of individuals with absolutely identical genes and absolutely uncorrelated environments would be extremely low” cannot be substantiated from the evidence at hand.

Similarity in General Mental Ability in Bedouin Full and Half Siblings.

Abstract A small battery of g loaded mental ability tests were administered to 274 children from 106 Bedouin families (mean age = 15.0 years, range of age = 7.9 – 18.9 years) attending grade schools in the southern region of Israel. The children were chosen on the basis of being members of families in which the father has two wives and the respondent having a sibling (half- or full-sibling) in the same school. The three measures (Raven, Digit Span and Pedigrees) yielded a large single general factor (the first unrotated principal component— g ) replicating their behavior in Western populations. Model-fitting with Mx demonstrated that a model with shared environmental and nonshared environmental influence could explain the data for all three measures as well as the g factor although it was not possible to exclude an additive genetic and nonshared environmental model for the Raven data. The full-sibling maximum likelihood correlation for g was .49; the half-sibling maximum likelihood correlation was .43. These correlations are essentially the same as those based on similar measures gathered on full-siblings and half-siblings of about the same age in Western populations. A contrast measure (Elithorn Mazes) was included in the battery of tests because it has shown little or no familial similarity in previous studies. Similar results were obtained for our full- and half-siblings as well (.0 and .15). These findings demonstrate internal validity for these tests in this cultural context and support the proposition that shared family environment is a strong determinant of sibling similarity for children in this age range.

Longitudinal Studies of Personality and Intelligence

In 1882 Sir Francis Galton called for the creation of “anthropometric laboratories”: The leading ideas of such a laboratory is I have in view, were that its measurement should effectually “sample” a man with reasonable completeness. It should measure absolutely where it was possible, otherwise relatively among his close fellows, the quality of each selected faculty. The next step would be to estimate the combined effect of these separately measured faculties in any given proportion and ultimately to ascertain the degree with which the measurement of sample faculties in youth justifies a prophecy of further success in life, using the word “success” in its most literal meaning. (Galton, 1885, p. 206)In 1882 Sir Francis Galton called for the creation of “anthropometric laboratories”: The leading ideas of such a laboratory is I have in view, were that its measurement should effectually “sample” a man with reasonable completeness. It should measure absolutely where it was possible, otherwise relatively among his close fellows, the quality of each selected faculty. The next step would be to estimate the combined effect of these separately measured faculties in any given proportion and ultimately to ascertain the degree with which the measurement of sample faculties in youth justifies a prophecy of further success in life, using the word “success” in its most literal meaning. (Galton, 1885, p. 206)

The Recaptured Scale Technique: A Method for Testing the Structural Robustness of Personality Scales

ABSTRACT Tellegen and Waller advocated a complex and time-consuming scale construction method that they called “exploratory test construction.” Scales that are constructed by this method—such as the Multidimensional Personality Questionnaire (MPQ)—are presumed to be more “psychologically coherent” and “robust” than scales constructed by other means. Using a novel procedure that we call the “recaptured scale technique,” we tested this conjecture by conducting a megafactor analysis on data from the 411 adult participants of the Minnesota Study of Twins Reared Apart who completed the MPQ, the MMPI, and the CPI. We extracted and obliquely rotated 21 factors from a matrix of gender-corrected tetrachoric correlations for the 1,102 nonredundant items of the three omnibus inventories. Robustness of the 11 MPQ scales was assessed by the degree to which these factors recaptured the MPQ item groupings. Our results showed that nine factors were clearly recognizable as MPQ scales and two additional factors represented a bifurcation of an MPQ scale. A higher-order factor analysis of all 21 factor scales yielded five factors that clearly resembled the Big Five. Our results provide strong support for (a) the method of exploratory test construction, (b) the structural robustness of most MPQ scales, and (c) the utility of the recaptured scale technique.

Intensive, Detailed, Exhaustive.

Arthur Jensens bibliography is characterized as breathtaking and his scientific work as intensive, detailed, exhaustive, fair-minded, temperate, and courageous. Specific articles and books are targeted as must reading. I argue that Jensens characterization of the influence of the Berkeley psychology department in the 1940s reflects his own intellectual biases rather than those of the department. Jensens work is praised as an extension of the British Biological-Theoretical Tradition which attempts to integrate psychological, biological, social genetic, sociological, and cultura processesl in a coherent theoretical framework. A new definition of Jensenism, based on the Jansenist heresy, is provided.

Discovery-Oriented Behavior and Problem Solving

Discovery-oriented behavior during the presolution stage of a problem-solving task was explored by videotaping and scoring the behavior of 60 male and female college students. They were presented with 14 different objects and told they would later have to suggest novel and useful combinations of three or more objects taken together. Behavioral variables that reflected touching and transformation of the objects were generated from the videotapes and correlated with number of solutions produced. Touching variables had high positive (significant) correlations with the criterion for females, but low positive (nonsignificant) correlations for males. Transformation variables had moderate negative correlations with the criterion for males (significant), but low negative (nonsignificant) correlations for females. Discovery-oriented behavior appears to be worthy of further study in the problem-solving domain.