6  The Gut Microbiome
SIDEBAR 1.1  Fire and Dietary Starch Led to Increased Hominin Brain
Size
The body is able to digest starch with the help of the enzyme amylase. Chim-
panzees, our oldest living relatives, have fewer copies of the amylase gene
compared to humans, which indicates that the number of amylase genes
increased during human evolution. Scientists previously hypothesized that the
emergence of agriculture led to higher starch consumption and thus increased
the need for amylase production. However, recent advances in biotechnology,
which allow scientists to analyze the DNA of early European hunter-gatherers,
show extra copies of the amylase gene in humans well before the beginning
of agriculture.
Some evolutionary geneticists argue that the advent of cooking fueled the
need for more amylase. Early foragers depended on starchy plants such as
tubers, and as they began cooking, the digestibility of these carbohydrate-rich
foods increased. Since amylase is more effective at breaking down cooked
rather than raw starch, heating starchy foods quickly gave this enzyme a more
significant role, and human DNA evolved to produce extra copies of the amy-
lase gene. These findings are raising many questions about the composition
of the hunter-gatherer diet and the importance of carbohydrates in human
evolution.
The food processing techniques of the Hadza are far more rudimentary
than those common in Western cultures. In addition to flash-fire cooking,
another processing technique used by the Hadza is the grinding of baobab
to make a coarse flour. When Hadza are out of camp, baobab is usually con-
sumed raw and unprocessed, but once it is brought back to camp, the pulp
and seeds can be pounded into a flour using a hammerstone. Whereas mod-
ern milling removes much of the fiber content to produce refined flours, the
Hadza method of grinding baobab flour retains much of the dietary fiber. The
combination of minimally processed foods and high intake of diverse whole
plant foods provides a variety of dietary fibers for the Hadza. This in turn has
implications for the gut microbiota, as many of these fibers are the primary
food source for bacteria. In this way, the Hadza diet directly promotes micro-
bial diversity within the gut.
The Hadza division of labor specifies particular roles for men and women.
These gender roles affect overall diet and are reflected in the slight differences
in gut microbiota composition between Hadza men and women. Although
both genders share any foraged food with the whole group, daily food intake
varies by gender. Men are more mobile foragers and travel farther away from
camp, searching for fruit, wild game, and honey, depending on seasonal
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