In adopting the position that human personality may be explained by one factor, researchers tend to call that factor the

Association studies of depression focus on genes that regulate the ______ system

a. sympathetic b. serotonergic c. parasympathetic d. limbic

Today, scientists tend to see emotions as ________ to survival and a ________ source of personal enrichment

a. unnecessary; major b. essential; major c. unnecessary; minor d. essential; minor