Homo sapiens history is millions of years. Then why we do not have contagious disease from millions of years ago. All the harshest contagious disease happened in couple decades. And they likely to stay in our specie's gene pool. such as HIV. How come it did not exist from millions of years ago? If it’s transmitted from monkey. We ate more monkey millions years ago. It is very mysterious. Since some disease like HIV will be likely to stay in our specie in the future but non-have stayed since millions years ago. And we did not even have medication for cure millions years ago. Isn’t it interesting? Can be new disease still happen to humans all the sudden? And why does it happen? If HIV existed in millions of years ago wouldn't we all be extinct? Or actually medication to prolong life is bad effect to the society as whole? Because its cause more people to be contaminated and not die naturally. Anybody know the answer?