Answer:
Behavior genetics
Explanation:
Behavior genetics is the most important field of science that studies the environmental and genetics influence on behavior. Many of the psychologist study about the influence of genetics on behavior. They studied not that what is genetics but they studied about what the effect of genetics on behavior. They explained how the genes and environment are affected by each other. There is a specific type of genes are responsible for specific behavior.
Thus here Dr. Cardin-ale was interested in the effect of heredity and environment on intelligence. He was studying behavior influenced by heredity by using behavior genetics.