when individuals who are biologically vulnerable to depression
Biological Causes. Some individuals are more vulnerable to depression than others due to their own unique biological factors, such as presence of depression-triggering genes. This means that depression is hereditary; hence it tends to run in families, notes the Black Dog Institute.nother biological trigger of depression is abnormal brain structure and chemistry. The report released by the National Institute for Mental health notes that the brain structure of an individual with depression is slightly different from the rest of individuals who do not have the disorder.