How did those observations lead to his theory about common descent with modification?

Discuss what Darwin observed during his voyage on the Beagle. How did those observations lead to his theory about common descent with modification?

Use the scientific method in your discussion.
Step 1: What did he observe?
Step 2: What was his hypothesis?
Step 3: What prediction was made based on his hypothesis?
Step 4: How can the prediction be tested using similar observations?
Step 5: What was the conclusion?
Your response must be at least 200 words in length.