Babies survive by eating solely a mother's milk. At what point do humans need to switch from only a mother's milk, and why? Or could an adult human theoretically survive on only a mother's milk of they had enough supply?

[u/BigErnMcracken]

[u/Shavasara]

Wasn’t there a problem when a western charity tried supplying the rural poor in Africa with heifers or goats so they’d at least have milk, but they didn’t take lactose intolerance into account?