Is there a definitive answer to this question? I do not think so. I have found no way to study life. But, I will admit this is the question that drove me to the study of biology. Sadly, biology can only study life systems, not life.
Personally, I "believe" the answer is God, and more specifically God's Spirit.
An equally interesting question is this: Why are some of us driven to invent or follow after religions?
The only thing I find easy to answer is: Why are some driven to reject religions? And that is, simply, because they resent what they see as systematic, human controls. I "believe" there is a rebel in all of us.