Years before Sarah Silverman decided not to have children, she mentioned her reluctance to have biological children because she may pass on the depression that runs in her family. Depression is highly heritable.
In my darkest moments, I’ve wondered if suicidal impulses are a mechanism to weed out genetic traits that make someone ill-suited for society, much as spontaneous abortions are the body’s mechanism to end a fetus that doesn’t seem viable. (“Seem” being a particularly messy idea, as are most things in nature.)
However, there is a theory that while the majority of humans have “dandelion genes” which allow them to thrive in almost all conditions they may find themselves in, some human’s mental health problems may be caused by “orchid genes” which, in turn, cause them to wither under most conditions but thrive in carefully cultivated hothouse conditions.