Appearance of teeth in the embryos of birds is an example of `:`

Options

A. vestigeal organs
B. ontogeny repeats phylogeny
C. atavism
D. speciation

Answer

To solve the question regarding the appearance of teeth in the embryos of birds, we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks what the appearance of teeth in bird embryos exemplifies. This requires knowledge of developmental biology and evolutionary concepts.

2. **Identifying Key Concepts**:
- **Ontogeny**: This refers to the development of an organism from the embryo to its adult form.
- **Phylogeny**: This refers to the evolutionary history and relationships among species.

3. **Recapitulation Theory**: The hypothesis proposed by Ernst Haeckel states that "ontogeny recapitulates phylogeny," meaning that the development of an individual organism (ontogeny) mirrors the evolutionary history of that organism's species (phylogeny).

4. **Applying the Theory**: In the case of birds, the presence of teeth in their embryos is an example of this theory. It suggests that during the embryonic development, birds exhibit features that are reminiscent of their ancestral lineage, which included teeth.

5. **Conclusion**: Therefore, the appearance of teeth in the embryos of birds is an example of the principle that "ontogeny recapitulates phylogeny," also known as the biogenetic law.

### Final Answer:
The appearance of teeth in the embryos of birds is an example of **ontogeny recapitulating phylogeny**.

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