Interest in the biological underpinnings of temperament has always been strong.
Genetic influence on temperament has been presumed either explicitly or implicitly in most conceptual frameworks. If temperament is not just environmental, then it must have an internal component which is likely at least partially genetic.
One theory, that of Buss and Plomin even included heritability in their definition of the construct. According to these theorists a temperament trait had to be early appearing, relatively stable and heritable to be included in their list of temperamental characteristics.
Their model included activity level, emotionality and sociability as the main components of temperament. Using twin studies they demonstrated that these elements of temperament were strongly influenced by genetics, accounting for perhaps half (50%) of the individual variation in each trait. Studies of other models of temperament using twins and behavioral genetic analysis have supported this view.
Additional studies have focused on the relationships between genetic and environmental variation within families and their effects on expressed temperament traits. One interesting finding is that siblings within a family become as different from each other as possible, because of their 'nonshared' environmental experience.
With the increased focus on genetic markers made possible by the mapping of the human genome it will be possible in future research to identify specific biological markers for temperament characteristics.