Interestingly on a related note I just watched a documentary called "The Workers Cup" about laborers building the venues for the Qatar world cup and there were many shots of the laborers manually shoveling rocks and gravel in places where you would typically see a machine doing it here in North America. Apparently, for them, it's cheaper to use cheap labor to hand dig rocks and dirt than to use a machine to do it.
Yes, if you can treat workers like machines (i.e. no “human rights”) they are actually more efficient per calorie/dollar than a rotary engine for many tasks.
This is why slavery didn’t just die upon invention of the engine.
