For half a billion years, all life on earth was microorganisms living under water. The reproductive cycle of these organisms mingled much with their digestive one, simply stated, eating and sex were one and the same thing. Not that those activities were defined as such, all was a bit more vague and less outspoken. A significant event occurred when one primitive prokaryote organism tried to eat another but failed to digest it successfully. The eaten one nested inside the gut of the other and together they fused to become the first eukaryote organism. Later on plants, animals and humans all came to be made from eukaryotic cells. In a way, all complex life stems from stomach problems.