Biological Factors Play a Role in Mental Illness

Biological factors play a role in mental illness. Which of the following is NOT a piece of evidence provided in your textbook to support this idea?

A) Medications developed for conditions other than mental illness have provided clues linking neurotransmitters to certain mental illnesses.
B) Fraternal twins are eight times more likely to have the same mental illness as are unrelated strangers.
C) Exposure to environmental toxins in childhood and adolescence may lead to mental illness.
D) PET scans demonstrate that some brain regions function differently in people with mental illness.