Briana N. Horwitz

IGEMS: the consortium on Interplay of Genes and Environment across Multiple Studies.

The Interplay of Genes and Environment across Multiple Studies (IGEMS) group is a consortium of eight longitudinal twin studies established to explore the nature of social context effects and gene-environment interplay in late-life functioning. The resulting analysis of the combined data from over 17,500 participants aged 25-102 at baseline (including nearly 2,600 monogygotic and 4,300 dizygotic twin pairs and over 1,700 family members) aims to understand why early life adversity, and social factors such as isolation and loneliness, are associated with diverse outcomes including mortality, physical functioning (health, functional ability), and psychological functioning (well-being, cognition), particularly in later life.

Gene-Environment Interplay in Interpersonal Relationships across the Lifespan

The Springer series Advances in Behavior Genetics focuses on the interdisciplinary area combining the behavioral sciences and genetics. The study of behavior genetics has become increasingly important as rapid advances in molecular genetic techniques lead to quicker discovery of genes involved in complex behavior disorders. It has now become a vast common ground for scientists from very diverse fields including psychology, psychiatry, neurology, endocrinology, biochemistry, neuroimaging, as well as genetics. The series Advances in Behavior Genetics seeks to document the changing landscape of the field as it continues to progress from comparatively small studies to consortiabased efforts that target the inherited components of complex diseases and behaviors with thousands of participants. With reviews of up-to-date literature of current topics and issues in behavior genetics the series will direct future research for students and researchers in behavior genetics.

Understanding The Role of Mate Selection Processes in Couples’ Pair-Bonding Behavior

Couples are similar in their pair-bonding behavior, yet the reasons for this similarity are often unclear. A common explanation is phenotypic assortment, whereby individuals select partners with similar heritable characteristics. Alternatively, social homogamy, whereby individuals passively select partners with similar characteristic due to shared social backgrounds, is rarely considered. We examined whether phenotypic assortment and/or social homogamy can contribute to mate similarity using a twin–partner design. The sample came from the Twin and Offspring Study in Sweden, which included 876 male and female monozygotic and same-sex dizygotic twins plus their married or cohabitating partners. Results showed that variance in pair-bonding behavior was attributable to genetic and nonshared environmental factors. Furthermore, phenotypic assortment accounted for couple similarity in pair-bonding behavior. This suggests that individuals’ genetically based characteristics are involved in their selection of mates with similar pair-bonding behavior.

Age-moderation of genetic and environmental contributions to cognitive functioning in mid- and late-life for specific cognitive abilities

Age moderation of genetic and environmental contributions to Digits Forward, Digits Backward, Block Design, Symbol Digit, Vocabulary, and Synonyms was investigated in a sample of 14,534 twins aged 26 to 98 years. The Interplay of Genes and Environment across Multiple Studies (IGEMS) consortium contributed the sample, which represents nine studies from three countries (USA, Denmark, and Sweden). Average test performance was lower in successively older age groups for all tests. Significant age moderation of additive genetic, shared environmental, and non-shared environmental variance components was observed, but the pattern varied by test. The genetic contribution to phenotypic variance across age was smaller for both Digit Span tests, greater for Synonyms, and stable for Block Design and Symbol Digit. The non-shared environmental contribution was greater with age for the Digit Span tests and Block Design, while the shared environmental component was small for all tests, often more so with age. Vocabulary showed similar age-moderation patterns as Synonyms, but these effects were nonsignificant. Findings are discussed in the context of theories of cognitive aging.