Cordain doesn't ask dieters to go completely caveman by consuming raw meat though. As long as our ancestors invented fire, we might as well use it to cook with. Still, some Paleo lifestyle worshipers choose to ignore the existence of fire, and they take their meat raw. Hunter-gatherers did just that - hunted and gathered. But the 21st-century carnivore goes down to their local grocery store and buys meat that's been processed through who-knows-what and who-knows-where. Our ancestors never dealt with a middle man.
Carbs from fruits and vegetables should provide plenty of nutrients, whereas grains fall into the "sugar" category, especially because of their starch content. Cutting out heavier carbs is said to change the way one's body metabolizes and utilizes fat.
As with any fad diet, there are the obvious critics. Environmentalists don't encourage meat consumption because of the harm done to the Earth when animals are hunted and processed through factories. Some archaeologists believe evolution has toyed with the human digestive process and metabolism, so the Paleo diet does not answer the needs of the 21st-century human.
Who knows how our ancestors would feel about this. But according to this Japanese commercial, maybe cavemen knew more about processed foods than we like to assume.