As the nature-versus-nurture debate rages on, recent research has opened up news ways of thinking about it. The debate has become far more interesting and complex. Emerging from current research is the finding that mental functioning and human behaviour are neither just nature nor just nurture alone. They are influenced by a complex interaction between both nature and nurture. Genetics (nature) is linked to mental health, personality, behaviour, mood and relationships in ways that interact with the growing-up environment (nurture). In order to understand this complexity, it is important first to grasp some basics about genetics.

The study of the gene is called genetics, which is derived from the Greek word genesis. This can be loosely translated as ‘origin’. Genetics is about the inheritance of traits. These traits are not limited to characteristics such as eye colour and predisposition to certain physical illnesses. They extend to human behaviour and mental conditions as well. Epigenetics refers to the way in which the intracellular or extracellular environment may switch gene transcription on or off. Life circumstances – including home and school life, relationships with caregivers and others, as well as anything important that happens in a child's world – can cause genes to become either silenced or expressed over time. Epidemiological studies suggest that genetics, or heritability, accounts for 40–50% of depressive disorders and 30–40% of anxiety disorders.

Psychologists are sometimes critical of the role genetics is said to play in mental health. There are important reasons for this scepticism. An attitude of ‘it's all in the genes’ can be reductionistic, disregarding the value and complexity of psychological theory and practice. Yet, although people and animals are quite different in many ways, it's important to note that some animals are bred precisely for purposes related to specific behaviour and temperament. The vital role of genetics accounts for why certain dogs are bred for human guidance and other kinds of dogs are bred to fight. Understanding genetics in relation to mental health is not a replacement for psychological theory and psychotherapy. It does, however, enhance and enrich the understanding of human behaviour, psychopathology and personality.