In practice it depends a lot on the environment you live in. As a general rule, the colder/drier the climate, the harder to live from plants alone. In some pla

In practice it depends a lot on the environment you live in. As a general rule, the colder/drier the climate, the harder to live from plants alone. In some places the only vegetation is mostly useless for humans, consisting almost only of cellulose, but this can sustain ruminants that can then be hunted or domesticated by humans. On the other hand, hunting in a tropical jungle is pretty difficult, but then you have an abundance of fruits and roots and so, your diet will have far less meat and a lot more plants.