No one knows. The point is when does life begin, not spiritual life. The soul is not physical and cannot be seen with our physical eyes. We can see and detect a heartbeat that proves a living human being at 5 to 6 weeks. That is a fact. You can ask religious people about the soul and you will probably get as many different answers as the number of people you ask. Not so about the heartbeat. That is something we know for a fact medically.