After ralph has been diagnosed with major depressive disorder, his doctor explains that depression often runs in families. which of the following factors is ralph’s doctor exemplifying?

Biological

Explanation:

Major depressive disorder  may be defined as a type of mood disorder in which the individual suffers from the long and intense feeling of sadness. This is also known as clinical depression.

The major depressive disorder can be run in the family as well. The biological factor plays an important role in these disorder. The factors like age, sex and other genetic factors are might responsible for the development of the condition of major depressive disorder.

Thus, the answer is biological.