"We may all be netted together" - Darwin. This picture is a great way to illustrate and explain the relations/interactions within all animals. Does not necessarily relate to sexual selection, but a good representation of all Darwin theorized of.
Darwin’s first sketch of the tree of life from one origin. Note the cross-bars for extinction — and that change is not conceived with some direction-as-progress. And notice Darwin’s simple words introducing the sketch, “I think…”