Plant foods containing high quantities of starch were essential for the evolution of humans. ~ English evolutionary biologist Karen Hardy et al
Much has been made about increased meat consumption driving greater brain wattage in early Homo by those ignorant about animal intelligence in general and human nutrition in particular. If anything, a diet of carnivorous scavenging would have rendered hominins no smarter than vultures (no insult to vultures intended). Even now, eating meat creates an unfavorable gut microbiome, degrading health and promoting mortality.
Any flesh early Homo consumed would have been raw meat, as cooking had yet to be discovered. The derived nutritional value would have been less than meat seared by heat, and it would have borne a serious risk of pathogens – a risk that survivors would take note of.
The optimal diet to feed the body and brain is from plant sources, high in carbohydrates with appropriate protein.
Hominins may have upped their protein intake a bit by eating grubs and adult insects. The often-bandied conclusion that a meat-heavy diet provoked Homo evolution, particularly cognitive advance, is absurd.
Instead, hominins probably became better foragers, having learned through experience and culture the nutritional and medicinal values of plants and their products. Mashing tubers and other root vegetables, with their ample carbohydrate content, may have been significant. This better explains the evolution of hominin guts and brains.
Protein-laden muscle mass – meat – digests down to animal fat and amino acids: not an apt energy source. Further, the acidic digestive environment and indigestible waste products from eating meat tax the system terribly.
Autophagy – recycling proteins, amino acids, and other nutrients from spent cells – provides considerable readily available structural material needed by the body. Autophagy plays a critical role in body maintenance and longevity. Even slight adaptations in autophagy could account for hominin gut changes.
The hominin brain has long required a lot of energy. That energy has always been supplied by plant foods: high in carbohydrates and providing a surfeit of balanced protein.
Archeological evidence points to hominin descent on a largely vegetarian diet. For one, foraging is much easier, and more reliable, than hunting.
2.3–1.2 MYA, Paranthropus was a robust savanna forager that had a varied seasonal diet, preferring fruit and nuts when available, but resorting to herbaceous vegetation when not – not dissimilar to lowland gorillas. While Paranthropus had a head, jaw, and teeth comparable to a gorilla, it did not have the gorilla gut.
2 MYA, Au. sediba, the last australopith, was a gracile omnivore with a small gut that harvested from the woodlands: living off fruits, nuts, leaves, and sedges, as well as plants such as papyrus or cypress. Small critters, including insects, were likely on the menu. Au. sediba‘s diet, while perhaps higher quality, was not strikingly different from that of chimpanzees.
Homo ergaster (1.9–1.4 MYA) – a putative ancestor to humans – was another omnivore with a small gut. Archeological finds of axes and hides suggests skinning animals, likely for clothing. How much raw meat H. ergaster ate is not known. A safer, more readily available fare was plant tubers. These tough but highly nutritious vegetables were likely processed with stone tools to require less chewing and render them more digestible. As with humans today, juicy tubers and roots were probably an important part of H. ergaster‘s diet, providing ample carbohydrates and protein in a wholesome balance.
Considering the health risks of a diet high in raw meat, and the relative ease of finding vegetative food, it is most likely that a more learned selection of plant produce played a dominant role in the descent of humans, especially before the advent of cooking.
Neanderthals were more inclined to carnivory than other hominins. That dietary preference may have been instrumental in their demise, as its tax on health limited their life at the same time their competitor – Cro-Magnon – was starting to have a significantly longer life span. Longer life meant greater cultural transmission between generations.
The value of steeped experience cannot be overestimated. Elephant groups are led by an elder matriarch. A group bereft of senior leadership fares poorly by comparison.
Seafood shows up on the menu much more recently than other meat. The Chinese were supplementing their diets with freshwater fish 40 TYA, but contemporaneous Mediterranean settlers ignored any watery bounty.