Q.Observe the picture given below. Name the naturalist and write the explanation given by him that evolution of life forms had occurred on the basis of this example. [Picture shows short-necked ancestral animals and progressively longer-necked giraffes feeding on trees.]

Concept: Lamarckian theory of evolution (use and disuse of organs, inheritance of acquired characters)

The naturalist is Jean-Baptiste Lamarck. The picture depicts his explanation for giraffe neck evolution through two core principles:

1. Use and disuse: Ancestral giraffes with short necks constantly stretched to reach higher leaves on trees. This continuous use caused their necks to elongate slightly during their lifetime.

2. Inheritance of acquired characters: The elongated necks developed through stretching were passed on to offspring. Over successive generations, this cumulative inheritance led to progressively longer necks. …

The Concept: Lamarckism and Use-and-Disuse

The picture illustrates one of the earliest systematic attempts to explain evolution. Before Darwin, the French naturalist Jean-Baptiste Lamarck (1744–1829) put forward a theory in his work Philosophie Zoologique (1809) that organisms change over time in response to their environment. His explanation rested on two central ideas:

1. Use and disuse of organs: Organs that are used extensively become stronger and more developed; those not used gradually weaken and may disappear.
2. Inheritance of acquired characteristics: Changes acquired during an organism's lifetime can be passed on to its offspring.

The giraffe's neck became Lamarck's most famous example. He reasoned that if generation after generation of giraffes stretched their necks to reach leaves on tall trees, each individual would develop a slightly longer neck, and this elongation would be inherited by the next generation. Over many generations, short-necked ancestors would give rise to the long-necked giraffes we see today.

Lamarck's Explanation of Giraffe Evolution

1. Ancestral giraffes had short necks and fed on lower vegetation. As competition for food increased or lower leaves became scarce, they were forced to stretch upward to reach leaves on taller branches.

2. Continuous stretching during an individual's lifetime caused the neck and forelegs to elongate slightly. Lamarck believed this physical change—acquired through effort and use—would be incorporated into the organism's body.

3. The acquired longer neck was inherited by offspring. Each generation started with a slightly longer neck than the previous one, and continued stretching further increased the length.

4. Over many generations, this cumulative process resulted in the modern giraffe with its characteristically long neck and legs. …