Species of early Homo were more flexible in their dietary choices than other species. Their flexible diet was aided by stone tool-assisted foraging that allowed our ancestors to exploit a range of resources. ~ Leslie Aiello
Apes tend to have large guts: a trait associated with an essentially herbivorous diet of low-nutrient vegetation. The same applied to early australopiths.
One of the shifts that started with later australopiths – but came to prominence with Homo – is a change in the digestive system. By 1.8 MYA hominin gut size had shrunk.
Tooth size also shrank. Homo is the only primate where the size of teeth dwindled as brain size grew. That must have reflected a change in diet.
In general, gathering and hunting groups live largely by gathering. Hunting is a difficult and hazardous activity with only intermittent rewards at best. ~ English historian Clive Ponting
Meat & Vegetables
Evolution in the hominin gut owed to a better diet and/or improved digestion. An amalgam of adaptations is likely to have been involved.
Scavenging was always part of hominid foraging. Early Homo retrieved heads left untouched by big cats and devoured the brains. In contrast, hunting required weapons.
Homo erectus was the first hominin that approached modern humans in stature, brain size, and chewing equipment. It appeared 1.5 million years before cooking became a common occurrence.
Stone tools made the difference. To improve mastication, early Homo pounded tubers into paste, chopped greens, and pummeled meat into small pieces.
Raw meat is tough and practically impossible to break down into swallowable pieces just by chewing it. ~ American evolutionary biologist Katherine Zink & American paleoanthropologist Daniel Lieberman
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Children are famously finicky about the greens they eat. It is a behavioral adaptation to a world where lots of plants are toxic. Phytophobia likely has a long lineage in hominids as an evolutionarily instilled precaution.