Why has God punished every human for one person's sin? God expelled Adam and Eve from the garden of Eden because Eve ate the fruit that God told her not to. And this let evil into the world. If God loves everyone, so much so that he let his son die for us, then why has every subsequent human and animal had to live and deal with the result of evil?

How does the Bible explain this, given that it says God is just?
There is an assumption in this question that is actually the very problem that the question addresses. 

This question assumes that in the exact same situation you would act differently than Adam and Eve would. However, why would you? Would a loving God not have placed the people in the garden that gave humanity the best chance at continuing at sinless existence? Adam and Eve were representatives of all of humanity. Do you think that if a better representative existed God would not have chosen them?

Yes Adam and Eve sinned, but the basic reason is that any human being placed in that situation would have done exactly the same thing. The temptation was very strong and they fell. 

This was God's plan. He intended for Adam and Eve to sin so that he could work out his plan and glorify himself all the more. The story of Adam and Eve points to Christ. 

Romans 5:17


  17 For if, by the trespass of the one man, death reigned through that one man, how much more will those who receive God’s abundant provision of grace and of the gift of righteousness reign in life through the one man, Jesus Christ! 


If sin entered through one man so salvation has also entered by way of one man. If we cannot acknowledge sin came through Adam then we cannot acknowledge the the sacrifice of Christ was sufficient.