of fuel...

[T]he Ice ages which dominated the last two million years of human evolution brought a low- carbohydrate, high- protein diet. Certain metabolic adaptations were therefore necessary to accommodate the low glucose intake. Studies in both humans and experimental animals indicate the adaptive (phenotypic) response to low- carbohydrate intake is insulin resistance... We propose that the low- carbohydrate carnivorous diet would have disadvantaged reproduction in insulin- sensitive individuals and positively selected for individuals with insulin resistance. Natural selection would therefore result in a high proportion of people with genetically- determined insulin resistance.