To what extent is human behaviour genetically determined?
Human behaviour isn’t only determined by genetics. The greatest factors that influence human’s
personalities are genetic inheritance and environmental factors. In some conditions, genes play a major
role in human behaviour, in other conditions, the environment plays a crucial role in human behaviour.
The nature versus nurture debate is one of the oldest issues in psychology. Nature refers to all of the genes
and hereditary factors that influence who we are, from our physical appearance to our personality
characteristics.(2) Nurture refers to all the environmental variables that impact who we are, including our
early childhood experiences, how we were raised, our social relationships, and our surrounding culture.(2)
The debate centers on the relative contributions of genetic inheritance and environmental factors to
human development.(2)
One way to do this is to study relatives who share the same genes (nature) but a different environment
(nurture).(1) Adoption acts as a natural experiment which allows researchers to do this. Environmental
parents and their adopted children do not share heredity and thus their resemblance can be attributed to
family environment. Empirical studies have consistently shown that adoptive children show greater
resemblance to their biological parents, rather than their adoptive, or environmental parents (Plomin &
DeFries, 1983; 1985).(1) Like adoption studies, twin studies support the first rule of behavior genetics;
that psychological traits are extremely heritable, about 50% on average.(1)
Behavioral genetics has demonstrated that multiple genes – often thousands, collectively contribute to
specific behaviors. For example, depression is thought to be influenced by around 1000 genes (Plomin,
2018).(1) Genetic influence has been found for most behavioural disorders (Plomin et al., 2001).(3)
Genetic influences are not limited to disorders, they also contribute to normal variation in personality
