> The lifetime risk of suicide among patients with untreated depressive disorder is nearly 20%. (Gotilb I, Hammen C. (2002). Handbook of Depression.)
https://www.dbsalliance.org/education/depression/statistics/
I'd call that significant, particularly considering the pace of evolution and how recently mankind started treating depression.
That being said, a (self-perceived) burden can free the tribe from their own weight without suicide: social withdrawal and isolation are fairly common in depression.
But as I said, that's just something I've occasionally pondered about. I might be wrong about it, as other users have already pointed out.