Factors essential for us to live.
Air, water, and food.
Clean air.
Exhaust fumes, factory smoke, indoor smoke, and cigarette smoke.
It is needed for life and health.
Water.
Rivers, inland reservoirs, ponds, and springs.
It is harmful to health.
Nutrition for energy, growth, and disease protection.
A clean, healthy, and balanced diet.
Chemicals.
Caves or tree burrows.
Stones and animal bones.
To hunt animals for food.
Leaves and animal skins.
Generating fire.
Eat cooked meat instead of raw meat.
Preserving meat and better clothing.
Nomad Age, Agricultural Age, Industrial Age.
It diversified with social progress.