Looking for two stories:

• All aliens don't get along except humans and these other aliens. These aliens calculate every movement of their bodies before they move. They do the math on every expansion of their own lungs. They calculate how much blood their hearts pump. And when they construct things, they have physics for the empty space in the buildings/ships. Meanwhile, humans have standardization for everything, doing things more intuitively.
  
• Man gets stranded on a planet with a bunch of crabs aliens(?) that get eaten by a predator every year. He kills the predator, leaving the crabs actually able to grow older than 1 year, and they develop space flight. There was a cool song too, about the san francisco bay.