Life is like chances of throwing a cent, where the chances go by line:
1 2 1; 1 3 3 1; 1 4 6 4 1 and so on.
So like there are infinite number of these sets, so there are infinite number of possible life's.
If You want to make a new life, then you have to interact with another life for the new life to born. The other life's are always watching you, because they cannot live without you.
You may ask: what was "who knows" years ago ? The answer is: everything was similar, because we love life and we do not bother thinking too much about it, because it is all alright for us.
That is my understanding of life.