But the Lord was very adamant - that was all man could have. Then the Lord called the monkey and gave him 20 years. 

"But I don't need 20 years", he protested, "ten is plenty for me." 

Man spoke up eagerly "Can I have the other ten?" the monkey graciously agreed. 

Then the Lord called the lion and gave him 20 years; and the lion, like the monkey, wanted only ten. 

Again man spoke up "Can I have the other ten?" the lion said of course he could. 

Then came the donkey and he was given 20 years - but, like the others, ten was sufficient. 

And again man pleaded; "Can I have the other ten?" 

All of which explains why man has 20 years of normal sex life - ten years of monkeying around - ten years of lion about it - and ten years of making an ass of himself.