How did Darwin explain the existence of different varieties of finches on Galapagos Islands?

Explanation

### Step-by-Step Solution:

1. **Observation of Finches**: Charles Darwin visited the Galapagos Islands and observed various small black birds, which later became known as Darwin's finches. He noticed that there were multiple varieties of these birds on the same island.

**Hint**: Think about the initial observations that led to Darwin's conclusions.

2. **Common Ancestral Stock**: Darwin concluded that all these finches evolved from a common ancestral stock that was primarily a seed-eating bird. This common ancestor diversified into different varieties based on their feeding habits.

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