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Difficulty: HardLamarck's Theory of Evolution

A botanist repeatedly prunes a species of shrub over its lifetime, causing it to develop a compact, stunted growth form. When seeds harvested from this pruned shrub are grown under normal, unpruned conditions, all offspring develop into full-sized plants of standard height. Which of the following conclusions best refutes Lamarck's theory of evolution based on this result?

  1. Acquired somatic modifications resulting from environmental manipulation are not transferred to gametes or inherited by offspring.Answer
  2. B
    Environmental stress directly induces genetic mutations that suppress growth only when pruning is actively maintained.
  3. C
    Disuse of growth hormones during pruning causes permanent organ atrophy that is counteracted by natural selection in the offspring.
  4. D
    Natural selection favors full-sized phenotypes only when soil nutrients exceed the threshold required for stunted growth.

Answer

Acquired somatic modifications resulting from environmental manipulation are not transferred to gametes or inherited by offspring.
Lamarck's theory of evolution proposed that organisms pass on physical features acquired during their lifetime to their offspring (inheritance of acquired characteristics). The experiment demonstrates that pruning—an environmentally induced somatic change—does not alter the genetic code in the plant's reproductive cells (germline). Consequently, the offspring inherit the unedited genetic instructions for normal growth, refuting Lamarck's proposed mechanism.

Step-by-Step Solution

1
Identify the key postulate of Lamarck's Theory of Evolution being tested.
Lamarck's theory relies on the inheritance of acquired characteristics (somatic changes developed during an organism's life are passed to offspring).
Understanding Lamarck's mechanism is essential to evaluating why empirical evidence refutes it.
2
Analyze the experimental observations.
The parent plant acquired a stunted phenotype due to artificial pruning (environmental intervention), but its offspring produced from seed grew to normal height.
This shows that bodily changes (somatic cells) caused by environmental factors do not alter reproductive cells (germ cells).
3
Deduce the biological principle that invalidates the Lamarckian claim.
Phenotypic changes in somatic tissues are not encoded in DNA within germline cells, thereby proving acquired characteristics cannot be inherited.
Modern genetics and Weismann's germplasm concept confirm that only germline mutations/variations are transmitted across generations.

Key Concept

Inheritance of Acquired Characteristics vs. Somatic and Germline Differentiation
Estimated Time:1m 30s
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Topics

Lamarck's Theory of Evolution

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