If Adam and Eve were the first humans and they had Cain and Able, where did the next generation come from?

one explanation is that they reproduced with their siblings. the article below explains this quite well...

They had more than two kids , Adam lived to be 930 years old. When God made man perfect but , sin made his body slowly deteriorate . Cain and his brother and sisters married each other . Inter family marriage was allowed till Leviticus 18:6. The human body ( genes ) deteriorated enough that God said no more marriage between inter families . ( birth defects etc..)

and, let me guess....you haven't read your "bible" either...it never ceases to amaze me of how many who will ask, and never do any research...just ask "blind questions" that they thought up "all by themselves!" lets see...here we have Adam, and eve...a man and a woman...and we now assume they didn't have sex? no more babies were born to them? and they didn't grow up and have more? without reading a bible, i can arrive at this....pure logic..."Peace!" :)

pick up the bible and read it....if your truly interested you'll take the time to read and understand