Summary: The Doctor is there to watch humanity leave earth.
The Doctor had a fondness for humans above almost any other race in the universe. They had such passion and determination; when they made up their minds to do something they never gave up. So when the day came for the human race to take their first faltering steps out into the universe, leaving the world of their birth behind, he was there, watching.
He’d nurtured the people of earth, watched them grow and develop, knowing what they would become in time. He’d done all he could to keep them on the right track. He felt so proud of them.