You conflate geometry and topology * . The topology of the human hand is right in front of you to examine. A lettuce leaf is like a disk plus a wavy boundary and noise. Broccoli is a tree. A bicycle is topologically complex object with high genus. A bad drawing of a hand can still has the right connectivity, it could be smoothly deformed into a realistic hand. Not true for most of these bicycle drawings.

* using "topology" to refer to the graph structure of the skeleton of the solid, not the typical mathematical meaning.