The Descent of Diet
Tell me what you eat, I’ll tell you who you are. ~ French politician Anthelme Brillat-Savarin
All primates are primarily frugivores: fruit eaters. A few species are also folivorous: leaf eaters. The human digestive tract is adapted to fruit and vegetable consumption, as are teeth and jaw muscles.
Humans evolved by their diet. The trend in early hominid species was toward larger teeth and thicker enamel, but that later reversed.
Homo habilis had teeth somewhat like australopiths: a bit smaller but lacking the heavy wear from the diet of tough, coarse foods that sustained australopiths. H. habilis was eating better: fruit, vegetables (including tubers), and nuts; very little, if any, meat.
H. erectus, a tool-making hunter and gatherer, had even smaller teeth; partly a product of cooking food, and so tenderizing it somewhat. Gathering brought fruit, nuts, and vegetables, which varied seasonally and by locale. Meat became a larger part of the diet with more successful hunting.
The hunting that brought down red meat, though perhaps satisfying, was never the best nutrition. Humans, while omnivorous, thrive on a variety of the ready energy sources found in plant-based carbohydrates. For optimal nutrition, meat has always had, at most, a limited place on the hominin menu.
The menus of little early humans were partly supplied from shifting shorelines. The earliest settlements were near bodies of water. Ancient lakes, rivers, and the oceans yielded a rich supply of nutrients more readily than a diet reliant upon cultivation of crops. Aquatic foods offered a varied, nutritious diet. This included grasses, papyrus shoots, algae, seaweed, fish, snails, mollusks, and shrimp.
Shellfish, loaded with omega-3 fatty acids crucial for healthy brains, may have fueled smarter Homo. Human mental powers were enhanced at the water’s edge.
The agricultural revolution that started some 6,000 years ago resulted in some tooth reduction, spurred by the frequent practice of cooking, which turned tough food soft and more easily chewed. Besides the ease of intake, cooking vegetables releases nutrients otherwise locked in cellulose.
Cooking also renders as ready fuel tubers that are otherwise difficult to chew and digest (unless mashed using stone tools: a hominid practice for millions of years). Some foods, such as sorghum, cassava, manioc, and linseed, become edible only by cooking, as they contain cyanogenic glycosides.
Cereal grains retain abrasive particles even when cooked, so tooth wear increased with the onset of agriculture. That has been reversed in recent times, to deleterious effect, by common consumption of highly processed foods.
Cooking promoted brain development in hominins by improving nutrient intake, as fruit is seasonal and varies widely by locale. Improved nutrition also allowed gastrointestinal organs to shrink – effectively trading brains for guts.