"The adoption of agriculture was necessitated by three factors: a  
rising human population, the extinction of large animals and the  
human physiologic protein ceiling.

The human physiologic protein ceiling is, in short, the upper limit  
of dietary protein that humans can digest. Small animals have less  
fat and more protein for their size than large animals do. The total  
protein content of a rabbit may be as high as 75%, with 25% fat,  
while a large animal may be only 35% protein and 65% fat. The maximum  
amount of protein humans can process at one time is about 35% to 40%.  
Therefore, using rabbits as a food source will rapidly exceed our  
protein ceiling, causing a syndrome referred to by early arctic  
explorers and frontiersmen as "rabbit starvation." Despite eating  
huge amounts of lean meat, men afflicted with rabbit starvation  
quickly became lethargic and developed diarrhea; death eventually  
followed."

http://www.vitaminb17.org/paleo_diet.htm

Jim Swayze