Any creature that can foresee its own death must learn to laugh or go mad.

In other words, it is a mistake to think that humor is the opposite of seriousness. Humor is the way humans deal with the essential grimness of our lives and their inevitable ends. A serious work that is lacking humor is in some sense missing this essential component of how humans react in serious situation to keep themselves sane.

The opposite of serious is light. You can be light without being humorous. Lightness is essentially the simple avoidance of the grimness of life. It is a way of dealing with the sadness of things by simply refusing to look at them. It is, in many ways, easier to be light if you avoid humor, because humor is always about the absurd, and human absurdity is in some way always about how we pretend we are not all going to grow old, get sick, and die.

It is also possible to be light in dealing with death. This is what the cosy mystery, the Murder She Wrote kind of show does. They present death merely as a puzzle to be solved, separate from its awfulness, it's heartbreak, and its waste.

Humor can be grim. Much of the best humor is very grim. The key is that when you use humor in a serious story, it be serious humor.

Writing seriously is hard -- mentally and emotionally hard as well as artistically difficult. It is possible that you are catching yourself writing something light because that easier and less traumatizing. In which case, cutting the jokes is not going to make it serious. You will need to rethink the whole piece in a more serious vein.

It is also possible that you are throwing in light jokes in a serious piece, in which case the fix would be to make the jokes serious rather than light (meaning the the joke accepts and acknowledges the grimness and absurdity of human life rather than avoiding it).

Any creature that can foresee its own death must learn to laugh or go mad.

In other words, it is a mistake to think that humor is the opposite of seriousness. Humor is the way humans deal with the essential grimness of our lives and their inevitable ends. A serious work that is lacking humor is in some sense missing this essential component of how humans react in serious situations to keep themselves sane.

The opposite of serious is light. You can be light without being humorous. Lightness is essentially the simple avoidance of the grimness of life. It is a way of dealing with the sadness of things by simply refusing to look at them. It is, in many ways, easier to be light if you avoid humor, because humor is always about the absurd, and human absurdity is in some way always about how we pretend we are not all going to grow old, get sick, and die.

It is also possible to be light in dealing with death. This is what the cosy mystery, the Murder She Wrote kind of show does. They present death merely as a puzzle to be solved, separate from its awfulness, it's heartbreak, and its waste.

Humor can be grim. Much of the best humor is very grim. The key is that when you use humor in a serious story, it be serious humor.

Writing seriously is hard -- mentally and emotionally hard as well as artistically difficult. It is possible that you are catching yourself writing something light because that is easier and less traumatizing. In which case, cutting the jokes is not going to make it serious. You will need to rethink the whole piece in a more serious vein.

It is also possible that you are throwing in light jokes in a serious piece, in which case the fix would be to make the jokes serious rather than light (meaning the the joke accepts and acknowledges the grimness and absurdity of human life rather than avoiding it).