"I think I was Dutch in a past life"

A harmless enough phrase in a conversation. I was, however, compelled to be a smart-ass. I wanted to say something like "Even if you go back 5000 years, you were bugs the whole way down."

Then I started wondering -- is that true? The biomass of bugs on Earth is gigantic but their lifespan is short. If I'm likely to be reborn as a bug, the life would end quickly and I'd have another shot at human. How much time would really need to pass between being human in different lives?

So this project was born. To try and math-out an answer to that question.