Since the human genome developed primarily in adaptation to an African equatorial ecological niche over the course of more than 2 million years, and other hunter-gatherer diets developed subsequent to the diaspora out of Africa some 50K years ago, I think that contemporary African or equatorial hunter-gatherer diets more likely represent the human evolutionary diet than, say, the Inuit diet.
Put otherwise, if the human lineage developed for 2 million years in Africa, then (for sake of argument) began living in the arctic 50 thousand years ago, the genome spent 98% of its developmental time in Africa, and only 2% in other ecological niches. Since the primate lineage leading to humans really extends back more than 6 million years in Africa, the time “out of Africa” amounts to far less than 2% of the time during which the human genome has evolved.
When we look at contemporary African or other equatorial hunter-gatherer diets, we find a significant intake of plant foods. For examples take a look at the following table:
|Tribe||Latitude||% Animal Food||% Plant Food|
|San (!Kung)||20° S||68||32|
|San (!Kung)||20° S||33||67|
Note that this table has two different reports for the San (!Kung) because two different researchers—Yellen (1977) and Lee (1968)—have reported different values, possibly reflecting seasonal or geographical variations. The variation of these two reports on San diet emphasize that equatorial hunter-gatherers generally had variable intakes of plant and animal foods. If you average the two reports for the San, you get a diet that hovers around 50% animal and 50% vegetal.
On average, these equatorial tribes obtained 46% of energy from animal food and 54% from plant foods. A hunter-gatherer diet providing 46% of energy as animal food and 54% as plant food will have a net alkaline residue due to the large amount of K-bicarbonate provided by plant foods.
To illustrate, I created the following example of a 2000 kcal diet which derives 44% of energy from animal foods and 56% from plant foods, using the San (!Kung) diet as a model (they get about one-third of their energy from mongongo nuts; I substituted walnuts).
This slide shows the plant:animal subsistence ratio of this diet by caloric contribution:
This slide shows the plant:animal ratio by weight of the foods:
This slide shows the macronutrient distribution of this diet:
Note that although more than three-quarters of the weight of this diet consists of plant foods (1212 g), it provides only 122 g of carbohydrate which supplies only 23% of energy. Although animal foods form only about one-quarter of the weight, they supply nearly half of the energy. Fat provided 52% and protein 25% of energy; 77% of energy comes from protein and fat. A diet can have three times as much plant food as animal food by weight, yet supply more than three-quarters of its energy as protein and fat and have a relatively low carbohydrate content. (For reference, on average, U.S. citizens consume about 50% of calories as carbohydrate, double the value of this H-G diet analogue.)
Finally, this slide shows the acid:base ratio of the diet:
If we take this perspective, then we would expect to find evidence of maladaptation among hunter-gatherers eating diets that diverge significantly from the African standard. Inuit diverge more than any other tribe, with a diet providing 90% of energy from animal foods. Compared to the African hunter-gatherer, the Inuit diet contains much less of some nutrients (e.g. vitamin C and potassium) and has a net acid, rather than the African alkaline, residue. The question then arises, did Eskimos suffer any negative health consequences that might support the idea that the human genome adapted to a diet more like the equatorial hunter-gatherers?
I’ll deal with that in my next post.