system
A chat on subreddit /r/NoStupidQuestions
human
This entirely depends what denomination you follow and what you think about literalism.

It says somewhere in Genesis that Adam and Eve went on to have more "sons and daughters". 

So what I was taught is that their sons got together with their daughters. But that was ok because they were a fresh new species and didn't have time to develop mutations in the DNA so inbreeding wasn't a problem.
gpt
That doesn't make since because the whole family would keep reproducing with each other with no out side DNA coming in. The human race would not have survived.