More outside than inside . . .
We also needed to be in the Habitable Zone and have a number of collectors like Jupiter and the other Gas Giants to run a bit of interference for us. Also a very large Moon, as the final blocker and as a stirrer to keep the Earth's mantle soft and the magnetosphere functioning at full power.
Growing up on Earth is a very complicated business.
Microbial, yes. Advanced take time and a lot of luck.