Which one the following is not correct?

Options

A. The work done on the evening primrose by Hugo deVries laid the foundation of the mutation theory.
B. Single-step large mutations are known as saltation and were considered to be the main factor in causing speciation.
C. Darwin advocated that variations are always large but heritable changes.
D. Branching descent and natural selection are the two key concepts of the Darwinian Theory of Evolution.

Answer

To solve the question "Which one of the following is not correct?", we will analyze each of the provided statements one by one to identify the incorrect one.

### Step-by-Step Solution:

1. **Evaluate the First Statement**:
- The statement mentions that the work done on the evening primrose by Hugo de Vries laid the foundation of mutation theory.
- This statement is **correct**. Hugo de Vries is indeed known for his work on mutations and how they contribute to evolution.

**Hint**: Check the historical contributions of scientists to understand if the statement aligns with their recognized work.

2. **Evaluate the Second Statement**:
- This statement claims that single-step large mutations are known as saltation and are considered the main factor in causing speciation.
- This statement is also **correct**. Saltation refers to significant changes that can lead to the formation of new species.

**Hint**: Recall definitions of key terms in genetics and evolution, such as "saltation" and "speciation."

3. **Evaluate the Third Statement**:
- The statement asserts that Darwin advocated that variations are always large but heritable changes.
- This statement is **incorrect**. Darwin emphasized that variations can be small and that they accumulate over generations, leading to evolution, which he referred to as "Descent with Modification."

**Hint**: Consider Darwin's theory and how it describes variations in populations over time.

4. **Evaluate the Fourth Statement**:
- The last statement indicates that branching descent and natural selection are two key concepts of Darwin's Theory of Evolution.
- This statement is **correct**. Both concepts are fundamental to Darwin's theory.

**Hint**: Familiarize yourself with the core principles of Darwin's theory to assess the validity of statements regarding them.

### Conclusion:
After evaluating all the statements, the incorrect statement is the **third one**: "Darwin advocated that variations are always large but heritable changes."

### Final Answer:
The answer is **Option 3**.

---