One day God came to Adam to pass on some news. "I've got some good news and some bad news", God said.
Adam looked at God and said, "Well, give me the good news first."
Smiling, God explained, "I've got two new organs for you. One is called a brain. It will allow you to be very intelligent, create new things, and have intelligent conversations with Eve.
"The other organ I have for you is called a penis. It will allow you to reproduce your now intelligent life form and populate this planet. Eve will be very happy that you now have this organ to give her children."
Adam, very excited, exclaimed, "These are great gifts you have given to me. What could possibly be bad news after such great tidings?"
God looked upon Adam and said with great sorrow, "The bad news is that when I created you, I only gave you enough blood to operate one of these organs at a time."