Mild depression or sadness can be evolutionarily functional by broadening one's field of vision, motivating problem-solving, and opening access to new perspectives.

“mild depression could be evolutionarily functional that you know obviously clinical depression — is debilitating in a lot of ways but you know low-grade sadness — Lincoln's Melancholy — we know one of one of the things it can do is broaden your field of vision — and you know for for many people sadness is a signal that something is not working and it can motivate problem solving — it can in some cases — open access to New Perspectives”