God says to Adam, "I have some good news and some bad news. What do you want to hear first?"
Adam says, "Tell me the good news first."
God says, "I'm going to give you a penis and a brain. You'll derive from these great pleasure and great intellect."
Adam replies, "Wonderful! But what's the bad news?"
God says, "I'm only going to give you enough blood supply to work one at a time."