Lamarckism

• According to him the characters developed by the organisms in their life time are  transfer to the next generation 

• It is described under 4 postulates 

1. Tendency to grow

2. Formation of new organs

3. Use & disuse of organs 

4. Inheritance of Acquired characters

1. Tendency to grow

• Every organism has a tendency to grow ta o certain limit due to internal force.

• The limit is determined by the organism itself. 

2. Environmental effect & Formation of new organs 

• Change in environment develops new needs to the organism 

• To fulfill the new needs certain modifications develop 

• These new modifications lead to the formation of new organs.

3. Use and disuse of organs

• Continuous use of an organ for longer period makes it well developed, strong & functional 

• Disuse of organs for longer period leads to reduction in size & becomes vestigial or  disappear

4. Inheritance of acquired characters 

• Any characters developed by the organisms due to structural changes caused by the use and disuse of organs known as acquired characters. According to Lamarck, such characters are transferred to the next  generation and new characters develop in each generation

• After many generations the collection of characters lead to the formation of new species.  

Examples 

1. Long-necked giraffe 

• According to Lamarck, the ancestor of long-necked giraffes was short-necked and short-limbed. It was the size of deer and graze on grasslands.

• As the grasses became scarce due to the change in climate, the giraffe started to stretch its neck and forelimbs to reach the leaves of trees.

• Therefore the size of limbs and neck slightly increased which is  transferred to the next generation  

• This process continue for long period and lead to the evolution of long  necked giraffe.

2. Aquatic birds like duck 

• Ducks have evolved from terrestrial ancestors which did not have webbed toes. 

• When the competition was increased on land some birds migrate to water in search of food.

• As they enter into the water new desires develop in birds to adjust to new habitats. 

• Therefore some new characters like web development in between digits help to swim in the water. 

Criticisms of Lamarckism or Drawbacks 

• Organisms evolve towards complexity but highly developed flowering  plants are smaller 

• Eyes are used continuously & constantly become defective instead of  improving 

• The powerful muscles of athletes & wrestlers are not transferred to their offspring.