According to the theory of evolution, it seems that there is one big cell that slowly evolved in order to produce all of the life that we see in this world right now. A lot of people who believe in this theory alone may be atheists or agnostics. There are some studies that show however that the theory of creation can also be connected to the theory of evolution.
This is because God may have prompted the large organism to slowly evolve in order to create and bring life to the various things that we see in the world right now. This is known to be theistic evolution. Over the past years, more and more people have started to believe in this.