Lamarckism
Lamarck said organs grow with use and shrink with disuse, and such acquired characters are inherited. The giraffe's long neck is his famous example.
Lamarck's four main ideas
- Internal vital force: living things and their parts tend to grow bigger.
- Effect of environment and new needs: a change in surroundings creates new needs. The body develops new organs or changes old ones to meet them.
- Use and disuse of organs: an organ used often grows bigger and stronger. An organ not used becomes weak and may disappear.
- Inheritance of acquired characters: changes gained during life pass to the young. Over many generations, a new species forms.
Lamarck's examples
| Example | Lamarck's explanation |
|---|---|
| Long neck of the giraffe | Its short-necked ancestors stretched their necks to reach leaves on tall trees. The longer neck passed to the young, generation after generation. |
| Snakes without legs | Their ancestors crawled through narrow burrows and stopped using their legs (disuse). The legs slowly disappeared. |
| Webbed feet of ducks | Their ancestors stretched their toes while swimming (use). Skin between the toes grew into webs. |
| Small wings of flightless birds (ostrich, kiwi) | They stopped flying (disuse), so their wings became small. |
What is an acquired character?
An acquired character is a change an organism gains during its own life. It comes from use, disuse or the surroundings. Examples are a wrestler's strong muscles, a scar and a pierced ear. Such changes affect only body cells. They do not change the sex cells (eggs and sperms). So they are not passed on to the children.
Why Lamarckism was rejected
- August Weismann cut off the tails of mice for many generations. Every new baby mouse was still born with a tail.
- Ears and noses have been pierced in India for generations, yet babies are born without holes.
- A blacksmith's strong arm muscles are not seen in his newborn child.
- Weismann's germplasm theory: only changes in the sex cells (germplasm) are inherited, not changes in body cells.
A kabaddi player builds strong legs by training, but the player's baby is not born with strong legs. Gains from use stay within one lifetime.
2 marks: “What are acquired characters? Are they inherited?” Changes gained in one's lifetime through use, disuse or the surroundings, such as strong muscles or a scar. They affect only body cells, so they are not inherited.
4 marks: “Explain Lamarck's theory with the example of the giraffe.” Four points: vital force, new needs, use and disuse, inheritance of acquired characters. Giraffe ancestors stretched their necks for tall leaves and passed on longer necks. Weismann's tail-cutting experiment disproved it.
Lamarck = U-D-I: Use, Disuse, Inherit what you acquire.