Control of fire by early humans
Changes to diet

Before the advent of fire, the hominid diet was limited to mostly plant parts composed of simple sugars and carbohydrates such as seeds, flowers, and fleshy fruits. Parts of the plant such as stems, mature leaves, enlarged roots, and tubers would have been inaccessible as a food source due to the indigestibility of raw cellulose and starch. Cooking, however, made starchy and fibrous foods edible and greatly increased the diversity of other foods available to early humans. Toxin-containing foods including seeds and similar carbohydrate sources, such as cyanogenic glycosides found in linseed and cassava, were incorporated into their diets as cooking rendered them nontoxic.

Cooking could also kill parasites, reduce the amount of energy required for chewing and digestion, and release more nutrients from plants and meat. Due to the difficulty of chewing raw meat and digesting tough proteins (e.g. collagen) and carbohydrates, the development of cooking served as an effective mechanism to efficiently process meat and allow for its consumption in larger quantities. With its high caloric density and content of important nutrients, meat thus became a staple in the diet of early humans. By increasing digestibility, cooking allowed hominids to maximize the energy gained from consuming foods. Studies show that caloric intake from cooking starches improves 12-35% and 45-78% for protein. As a result of the increases in net energy gain from food consumption, survival and reproductive rates in hominids increased. Through lowering food toxicity and increasing nutritive yield, cooking allowed for an earlier weaning age, permitting females to have more children. In this way, too, it facilitated population growth.

It has been proposed that the use of fire for cooking caused environmental toxins to accumulate in the placenta, which led to a species-wide taboo on human placentophagy around the time of the mastery of fire. Placentophagy is common in other primates.
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