This video by Festo shows some amazing autonomous penguins – some swim and some fly. I was struck by one quote, noting that the swimming robot penguin does something living penguins cannot – back up. Sure enough, I’ve never seen a swimming penguin move backwards except when tossed by a wave. Thinking about the musculature of the penguin wing, the muscles and tendons are designed perfectly for transferring thrust from the wing back to the body, but only in one direction. Adding a “reverse gear” seems like it would be possible, but it would involve extra mass near the front of the penguin, which would be costly. Penguins seem to have foregone this solution, as they can just turn around in a rapid spin when they need to head in the other direction.