More than a century has passed since the first twin and adoption studies of behavior were conducted in the 1920s, but the study of behavioral genetics has only flourished with the advent of technological advancements. As we begin to perceive a clearer picture of the gene-environment interactions that influence behavioral patterns, the need to approach the field from an ethical and social perspective remains to be one of the greatest challenges for the study of behavioral genetics.
To illuminate the complexities behind the study of behavioral patterns, we attempt to shine the spotlight on the backstage happenings of human behavior, unravel the dynamic interplay of genes and environment, and bring the immersive study of behavioral genetics to the centerstage.
Estimating Gene-Environment Interactions
In 1937, the first twin study of intelligence in identical twins who grew apart was conducted by Newman et al., which aimed to investigate the interplay of heredity and environment. As more genetic studies on behavior emerged, it was gradually established that most behavioral and psychological traits have gene-environment interactions (Plomin, 2023). However, methods to elucidate such interactions did not exist till Jinks and Fuller devised one in 1970. Hailed as a breakthrough in behavioral genetics, the Jinks and Fuller test is an estimation method based on the regression of absolute differences of monozygotic (MZ or identical) twin-pair scores on the sums of MZ twin-pair scores. For identical twins reared apart, the differences in twin-pair scores is an estimate of all postnatal environmental influences. Whereas, for identical twins reared together, the difference only serves as an estimate of the environmental effects unique to individuals within a family.
The estimation of gene-environment interactions also propelled single-gene research, and further technological advancements in genetics allowed genome-wide association studies (GWAS) of complex traits. Results of GWAS allowed the creation of polygenic scores to predict individual differences for complex behavioral traits, giving birth to the budding field of behavioral genomics.
Twin Studies
Twin studies are often heard in conjunction with behavioral genetics—but how are they exactly conducted? The degree of genetic and environmental influence on a behavioral trait is attained through comparisons between monozygotic (MZ, or identical) twins and dizygotic (DZ, or fraternal) twins. Twin studies assess the resemblance of MZ and DZ twins, since MZ twins share all of their genes, while DZ twins share 50% of their genes, on average. The extent of genetic and environmental factors affecting behavior or psychological disorders between twins could help us develop better prevention and treatment methods.
The Heritability Coefficient
What does it mean when they say that criminal behavior is heritable by 45% for both sexes? Or that relatives of individuals with an eating disorder (ED) are 11 times more likely to develop the condition than relatives of individuals without an ED?
The heritability coefficient is overtly emphasized in the study of genetic behavior, but the implications of such outcomes are not properly communicated to the public. Instead, genetic determinism, or the belief that human behavior is solely dictated by one’s genes inherited from one’s parents, saturates public conversation regarding behavioral genetics.
Similar to how the field has advanced from single-gene research to multivariate analyses, such rigid approaches toward understanding human behavior must be discarded, allowing the general public to understand that the heritability coefficient elucidates only a fraction of behavioral knowledge.
Social class, quality of education, and parenting are just among the environmental factors that affect human behavior, as examined by genetic research. Social interventions such as early literacy and education are some methods that could be done during childhood. The knowledge gleaned from behavioral genetic research can aid us in improving the social aspects mentioned, and conversely, prevent aberrant genetic influences from unfolding.
Behavioral genetics offers a fascinating glimpse into human behavior, which should be approached in a multifaceted manner where environmental influences are given as much importance as genetic factors. After all, we are all given blueprints, but it is up to us to use our experiences and build on our genetic makeup.
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