The heirarchical organization of biologic diversity For evidence of common descent, look at the heirarchical distribution of various biological traits. DNA sequence data is extremely good for this sort of thing, but all the above examples also fit. The grouping of biological traits only makes sense when you assume all organisms share a common ancestor, and subgroups of organisms share common ancestors and so on. It is due to common ancestry of groups and groups within groups and groups within groups within groups and etc. I should point out that a heirarchical pattern to biological traits does not neccessarily mean the mechanisms of evolution need to be heirarchical to produce them.
Evolution is a successful predictive theory.
The hierarchy explained above is not only an observation, but a prediction. Any new traits surveyed should fall with previously established hierarchies. Recent advances in molecular biology have shown what a solid, predictive theory evolution is. Phylogenies used to be based primarily on morphological data. Phylogenies drawn from DNA sequences match morphological trees in almost all cases.