Picture our galaxy as a petri dish.
The first 'germ' to learn how to spread itself, even slightly, eventually occupies the entire petri dish.
If the dish is seeded with one life form, and it never develops the ability to spread, the dish remains empty. Then what if there are 2 different germs? 10? 10,000?
See, if there is only one or a very few, it's an empty dish for a very long time. Give life 10,000 bites at the apple, the first one to develop the spreading ability wins the prize. And the time it takes to fill the dish (galaxy) is almost insignificant to the amount of time it has been around.
The first 'germ' to learn how to spread itself, even slightly, eventually occupies the entire petri dish.
If the dish is seeded with one life form, and it never develops the ability to spread, the dish remains empty. Then what if there are 2 different germs? 10? 10,000?
See, if there is only one or a very few, it's an empty dish for a very long time. Give life 10,000 bites at the apple, the first one to develop the spreading ability wins the prize. And the time it takes to fill the dish (galaxy) is almost insignificant to the amount of time it has been around.
