Steel plough and incandescent light bulb: what they have in common

1. Step 1. Steel plough — evolved from — Plough. A steel share.
2. Step 2. Plough — evolved from — Hoe. The plough mechanized loosening the soil with a hoe.
3. Step 3. Hoe — is made of — Stone. The working part was of stone or antler.
4. Step 4. Stone — is material for — Oil lamp. The first lamps were stone bowls (Lascaux).
5. Step 5. Oil lamp — evolved into — Incandescent light bulb. The electric lamp replaced oil and gas lamps.

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