Alcohol
One of the early transformations from cavemen to modern humans occurred 9000 years ago when alcohol was introduced to human diets. Domestication of plants and animals signaled the end of the stone age, and yeast, which produces alcohol from sugar, was one of the first organisms humans domesticated. Alcohol is clearly not paleolithic for these reasons.
Paleo prescriptions are supported by governmental recommendations. Excessive alcohol intake has been linked to a variety of health problems, including liver damage, cancer, and weight gain. As a result, the FDA recommends limiting alcohol consumption to one alcoholic beverage per day for women and two alcoholic beverages per day for males.