Peer-reviewed article

Is Depression Nature or Nurture? Yes

Myrna M. Weissman · 28 Apr 2020

Abstract

I've increasingly felt that the correct answer to the question "Is depression nature or nurture?" is "yes."In a landmark study in this issue, Kendler and colleagues (1) put substance to this answer.While the answer may still be "yes," through the use of a cleverly designed natural experiment, Kendler et al. have identified a portion of nurture, the rearing environment, that can clearly be defined and even altered with intervention.In brief, they studied 666 high-risk full siblings, with high risk defined as having at least one parent with major depression, and 2,595 high-risk half siblings of which at least one was home-reared and one adopted away.What made this study possible were the large samples from a national registry in Sweden, the parental assessments, and the fact that in Sweden, where adoption is not common, adoptive families are selected to provide high-quality rearing environments, including high educational status, economic security, and a stable environment.It is impressive that this study comes from an investigator group that has done major genetic and twin studies.In both types of studies, the nature of the environment is unclear.Similarly, the adoption studies, another way of studying environmental effects, usually have had insufficient information on the biological parents and their clinical state.As the authors point out, biological parents of adoptees likely have a higher risk of psychopathology, less education, and higher divorce rates.Moreover, the environment in the adopted-away home has not been clearly defined in most studies.In fact, the authors previously carried out an extended adoption study in the same sample and had shown statistically that genetic factors and rearing experiences contributed to an approximately equal extent (2).Both forms of cross-generational transmission act additively on the risk for depression in the offspring.However, the contribution of the rearing environment was only shown statistically.These challenges in this and other previous reports must have led the authors to this study design.The findings confirmed the strong protective effect of a nurturing rearing environment on the child's well-being.However, this protective effect disappeared when an adoptive parent had major depression or the nurturing adoptive home was disrupted by parental death or divorce during the adoptee's childhood or adolescence.The results demonstrate the strong impact of the rearing environment on risk for major depression and support the importance of intervention efforts to improve the rearing environment in highrisk families.