Behavioural genetics
Behavioural genetics is the field of biology that studies the role of genetics in animal (including human) behaviour.  The field is an overlap of genetics, ethology and psychology. Classically, behavioural geneticists have studied the heritability of behavioural traits.

# History
In 1869, Francis Galton published the first empirical work in human behavioural genetics, Hereditary Genius.  Here, Galton intended to demonstrate that "a man's natural abilities are derived by inheritance, under exactly the same limitations as are the form and physical features of the whole organic world."  Like most seminal work, he overstated his conclusions.  His was a family study on the inheritance of giftedness and talent. Galton was aware that resemblance among familial relatives can be a function of both shared genes and shared environments.  Contemporary behavioural genetics studies special populationsin human research, twins and adoptees and in animal research, specially bred strains and linesto separate genetic from environmental effects.
The initial impetus behind behavioural genetic research was to demonstrate that there were indeed genetic influences on behaviour.  In psychology, this phase lasted for the first half of the 20th century largely because of the overwhelming influence of behaviourism in the field.  Later behavioural genetic research focused on quantitative methods, and today there is a large emphasis on applying techniques from molecular genetics to isolate individual genes that influence behaviour.

# Contemporary behavioural genetics
Currently, the largest branch of behavioural genetics is psychiatric genetics which studies phenotypes such as schizophrenia, bipolar disorder, and alcoholism.
Recent trends in behaviour genetics has indicated an additional focus toward researching the heritability of human characteristics typically studied in developmental psychology.  For instance, a major focus in developmental psychology has been to characterize the influence of parenting styles of children.  However, in most studies, genes are a confounding variable. Because children share 50% of their genes with each parent, any observed effects of parenting styles could be effects of having many of the same genes as a parent (e.g. harsh aggressive parenting styles have been found to correlate with similar aggressive child characteristics- is it the parenting or the genes?).  Thus, behaviour genetics research is currently undertaking to distinguish the effects of the family environment from the effects of genes.  This branch of behaviour genetics research is becoming more closely associated with mainstream developmental psychology and the sub-field of developmental psychopathology as it shifts its focus to the heritability of such factors as emotional self-control, attachment, social functioning, aggressiveness etc..
Several academic bodies exist to support behavior genetic research, including the International Behavioural and Neural Genetics Society, Behavior Genetics Association and the International Society for Twin Studies.Behavior genetic work features prominently in several more general societies, for instance the International Society for Psychiatric Genetics and the International Behavioral Neuroscience Society.

# Methods of behavioural genetics
Behavioural geneticists use several designs to answer questions about the nature and mechanisms of genetic influences on behavior. All of these designs are unified by being based around human relationships which disentangle genetic and environmental relatedness.
So, for instance, some researchers study adopted twins: the adoption study. In this case the adoption disentangles the genetic relatedness of the twins (either 50% or 100%)  from their family environments. Likewise the classic twin study contrasts the differences between identical twins and fraternal twins within a family compared to differences observed between families. This core design can be extended: the so-called "extended twin study" which adds additional family members, increasing power and allowing new genetic and environmental relationships to be studied. Excellent examples of this model are the Virginia 20,000, and the QIMR twin studies.
Also possible are the "children of twins" design (holding maternal genetic contribution equal across children with paternal genetics and  family environments; and the "virtual twins" design - unrelated children adopted into a family who are very close or identical in age to biological children or other adopted children in the family. The classical twin study has been severely criticized and is used less and less frequently nowadays.