Families and Genomes: The Next Generation

"I thought this was about family relations and child development. Why are we reading and talking about genes?" . Many of us who teach and study genetics and human behavior get questions like this from our students and our colleagues. My answer to this kind of question is informed by the ongoing work presented by Horwitz and Neiderhiser (2011), and it goes something like this: Our cultures and our genomes have coevolved for millennia. The continually changing products of this ongoing process include different versions of many genes (i.e., alleles) that covary and interact with variability in environments. Efforts to understand the impact of this ongoing process require consideration of family relationships. Successful reproduction and survival of offspring are ensured within the intense, lifelong social relationships formed in family groups, where individual differences between people develop. Over the course of the 20th century, theorists in every scientific discipline came to realize that they needed to incorporate genetic influences into conceptualizations of human functioning and behavior. Now we find ourselves living in the era of the genome. Every week, new discoveries are published that tell us something about genes and their influence on human functioning. So here is my question. As students and scholars of family and human development, will we be able to move family and developmental research and practice toward a more complete understanding of the role of genetics in family relations and child outcomes? We probably will succeed, if we take seriously the important and complex concepts, methods, and conclusions offered by Horwitz and Neiderhiser (201 1) in their review of behavioral genetic research on family relationships and child adjustment. They present the breadth and leading edge of genetically informative research addressing gene - environment interplay in marital and family relationships and outcomes in children. Their paper offers a clear and compelling message about what we know, and what lies ahead, for family and developmental scientists. Theories about gene - environment transactions are tested using quasi-experimental behavioral genetic studies based on different types of kin (e.g., adoptive and nonadoptive parent -child pairs, identical and fraternal twin siblings, full and half siblings) and molecular genetic studies that directly assess the structural variation in DNA and its associations with behaviors of interest. Gone are the days of simply estimating a heritability coefficient and arguing that this variable or that variable includes some kind of genetic influence. Now there are computational methods for considering gene - environment interplay between genetic and nongenetic factors. This includes the correlated and interacting effects highlighted by Horwitz and Neiderhiser. FAMILIES AND GENOMES Gene -environment interplay produces remarkable within-family variation in each individual's many personal attributes, as well as variation in each dyadic relationship. Paying attention to this within-family variability - rather than limiting the analysis to differences between families or groups - strengthens understanding of the bidirectional nature of family relationships and children's development in families (Reiss, Neiderhiser, Hetherington, & Plomin, 2000). Within families are substantial sibling differences in temperament and personality factors, cognitive and achievement skills, and many other individual difference attributes arising from genetic and nongenetic influences. Full siblings share 50% of their alleles identical by descent, on average, but there is noteworthy deviation from this average level of genetic similarity. The physical and behavioral similarity of siblings varies widely, due in part to variation in genetic similarity. But nongenetic factors matter, too, and are defined as nonshared environmental processes that enhance sibling differentiation. The behavioral genetic models described by Horwitz and Neiderhiser (201 1) generate mathematical constructs representing heritable and nonheritable influences. …