This study constitutes a multitask appraisal of cerebral hemisphere specialization with 13 monozygotic (MZ) twin pairs discordant for handedness. Tasks included dichotic listening, finger tapping with concurrent loads, two tachistoscopic visual half-field tests, and a free-vision face test. Overall, MZ twins showed similar performance asymmetries on most tasks. Different asymmetries, however, were observed on the finger tapping with anagram load and visual half-field with chair stimuli. In these instances, asymmetries for left- and right-handed MZ twins were more similar to patterns reported in the literature for left- and right-handed singletons, respectively, than for opposite-handed co-twins.

Adolescent↗

PubMed1998

Behavioral genetics and evolutionary psychology: unified perspective on personality research.

Behavioral geneticists and evolutionary psychologists have generally pursued human behavioral analyses with little theoretical or methodological exchange. However, significant benefits might accrue from increased communication between these disciplines. The primary goals of this article are (1) to identify meaningful junctures between behavioral genetics and evolutionary psychology, (2) to describe behavioral genetic research designs and their applications to evolutionary analyses, and (3) to reassess current personality research in light of behavioral genetic and evolutionary concepts and techniques. The five-factor model of personality is conceptualized as subsuming variation in normative species-typical systems with adaptive functions in the human environment of evolutionary adaptation. Considered as universal evolved mechanisms, personality systems are often seen in dynamic conflict within individuals and as highly compartmentalized in their functioning between settings. However, genetically influenced individual differences in personality may also be understood within an evolutionary framework. Studies of the heritability of personality traits indicate broad-sense heritabilities in the 0.40-0.50 range with evidence of substantial nonadditive genetic variation and nonshared environmental influences. Evidence indicates that evolutionary theory (e.g., inclusive fitness theory) predicts patterns of social interaction (e.g., cooperation and bereavement) in relatives. Furthermore, variation in personality may constitute a range of viable strategies matching the opportunities available in the complex niche environment of human societies. Within this wide range of viable strategies, personality variation functions as a resource environment for individuals in the sense that personality variation is evaluated according to the interests of the evaluator (e.g., friendships, coalitions, or mate choice).

Biological Evolution↗

PubMed1996

Twin children with unfamiliar partners: genotypic and gender influences on cooperation.

This study applied a social-genetic perspective to examine hypotheses concerning displays of cooperation. The sample included children from 14 monozygotic and 16 dizygotic twin pairs, organized into 30 unfamiliar partnerships. Two puzzle completion sessions were videotaped and evaluated on five dimensions of cooperation. Repeated measures of analysis of variance indicated significantly higher ratings among female than male pairs on Overall Cooperation, Mutuality of Goal and Accommodation. Contrary to expectation, social-interactional differences between unfamiliar MZ and DZ dyads were not detected. Findings are discussed with reference to new research perspectives on cooperative behavior.

Adolescent↗

PubMed1995

Twin analysis of odor identification and perception.

Findings from the first twin analysis using the University of Pennsylvania Smell Identification Test (UPSIT) and a phenyl ethyl alcohol (PEA) threshold detection test are presented. A genetic influence on odor identification was suggested for males, but not for females, consistent with previous twin research on physical measures. In addition, females scored significantly higher on the UPSIT than males. A curvilinear age trend for odor identification was detected for males, but not for females. In contrast, neither genetic, age, nor gender effects were suggested for PEA sensitivity. Performance on the olfactory tests was unrelated to scores on standard measures of intelligence.

Adolescent↗

PubMed1995

Attempted suicide among living co-twins of twin suicide victims.

OBJECTIVE: The authors hypothesized that significantly more living monozygotic than dizygotic co-twins of twin suicide victims would themselves have attempted suicide. METHOD: They determined the absence or presence of an attempt at suicide at any time among 26 living monozygotic co-twins and nine living dizygotic co-twins of twins who had committed suicide. RESULTS: They found that 10 of the 26 surviving monozygotic co-twins but none of the nine surviving dizygotic co-twins had themselves attempted suicide. CONCLUSIONS: Although monozygotic and dizygotic twins may have some differing developmental experiences, these results contribute to findings of previous studies of suicide in twins in suggesting that genetic factors may play a role in suicidal behavior.

Adolescent↗

PubMed1995

Document the method of twin classification. Twins with pulmonary adenocarcinoma.

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Adenocarcinoma↗