Digging is an instinctive behavior ingrained in human DNA.
The entrance to the deep cave is narrow and easy to defend but difficult to attack.
In winter, it provides warmth, in summer, protection from rain, and it can also shield against cold winds and scorching sun.
Primitive people lit fires in caves to survive the cold, long Ice Ages.
They hunted mammoths, fought fiercely with beasts like the blade-toothed tiger, giant ground sloth, and cave bear, and used fur and grease to keep warm, sheltering their wounded tribesmen, young children, and women and elderly people.
In that wild era, the continuation of the human race was once in jeopardy.
At the mountain-top cave relics, burned animal bones and broken ape-man skeletons were not far apart.
For reproduction, for survival, the ancestors of humans repeatedly contested caves with ferocious cave lions and cave bears.
Eventually, our ancestors defeated them with fire, wisdom, and unity.
