Animal behaviour arises from a complex interplay between genetic predispositions and environmental influences. This paper examines how heredity and external factors jointly determine behavioural patterns in animals, drawing upon evolutionary theory, quantitative genetics, and empirical research. We review evidence showing that a substantial proportion of behavioural variation is heritable while environmental conditions modulate the expression of genetic potential. Behavioral genetics has become an increasingly important field as modern technology has allowed researchers to locate specific genes and alleles responsible for some behaviors. The field has also stirred controversy: people are hesitant to attribute behavior to genetics in the age- old nature versus nurture debate. But nature versus nurture is a false dichotomy. The truth is that both can play a key role in determining a behavior. The genotype determines the potential for a behavior to exist, while nature determines what phenotypic behavior actually results. The domestication process has frequently reduced the sensitivity of animals to changes in their environment, perhaps the single-most important change accompanying domestication. It has also resulted in modified rates of behavioral and physical development. Interest in breeding animals in captivity for release in nature has flourished in recent decades. The capacity of domestic animals to survive and reproduce in nature may depend on the extent to which the gene pool of the population has been altered during the domestication process and flexibility in behavioral development. Natural gene pools should be protected when breeding wild animals in captivity for the purpose of reestablishing free-living natural populations.