The theory " ontogeny recapitulates phylogeny" was proposed by

Options

A. Mendel
B. Haeckel
C. Erasmus
D. Weismann

Answer

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the scientist who proposed the theory "ontogeny recapitulates phylogeny." This theory suggests that the development of an organism (ontogeny) mirrors the evolutionary history of that organism's ancestors (phylogeny).

2. **Analyzing the Options**:
- **Option A: Mendel** - Gregor Mendel is known for his work on the laws of inheritance and genetics. He is not associated with the theory in question.
- **Option B: Haeckel** - Ernst Haeckel is known for proposing the theory of recapitulation, also known as the biogenetic law, which states that ontogeny (development) recapitulates phylogeny (evolutionary history).
- **Option C: Erasmus** - Erasmus Darwin, the grandfather of Charles Darwin, contributed to early ideas of evolution but did not propose this specific theory.
- **Option D: Weissmann** - August Weismann is known for his germ plasm theory but is not related to the theory of recapitulation.

3. **Identifying the Correct Answer**: Based on the analysis, the correct answer is **Option B: Haeckel**. Ernst Haeckel proposed the theory "ontogeny recapitulates phylogeny" in 1866.

4. **Conclusion**: The theory "ontogeny recapitulates phylogeny" was proposed by Ernst Haeckel.