I'm surprised that 40% was the number given. I bet it is more like 80%.
As far as the planet being overpopulated, I would definitely say no. I have done some travelling around and their are huge expanses of empty land out there just ripe for settlement. I believe that the Earth could support about 200 billion people comfortably. Maybe the area you live in is overpopulated but I wouldn't say the Earth as a whole is.