A person comes out, they live for a thousand years doing whatever they do, and then, when it's time to go back for a billion years — or a million, I forget, the numbers don't matter — but there really aren't very many people on Earth at a time.
Sale una persona, vive mil años haciendo lo que sea, y entonces, cuando hay que retroceder un millardo de años -o un millón, lo olvido, las cifras no importan- en realidad no hay mucha gente en la tierra a la vez.