I am who I am... That is why I am here... If I am not here, how can I say "I am here?"...
The inductive conclusion is in this way: I am that I am. If I am not who I am, who is the one who is speaking to you now? Actually, that is a very very BIG question similar to ask why 1+1=2. To disclose this question, I should ask the existence of myself, the value of myself in this world and so forth. Note that "我思故我在”. The nature of your question is something to do with philosophy, not anthropology. Thus, you should consider why you are asking this question and how you are planning to solve this mystery first. Instead of doing so, try to study philosophy in order to grasp the whole figure of your answers.
Aware that there are two portions of "self" for all individuals. One is physical part and another non-physical in spirit. With these two compositions, a human is then called a human "being". Lack of any, this individual cannot be considered as "self" with senses stated herein. In the scientific domain, we can indeed test what the phenomena of living lives are about; however, the spiritual portion is the territory that experiments cannot be carried out to verify. That needs "FAITH" in religion to answer it, but still cannot be tested by experiments. That is why your questions cannot be answered in scientific terms as far as I can see. However, there are some studies (see reference 2 for background information) still ongoing in ripening Neuroscience that may provide you some clues, but no answers so far. This is all right for some situations, as humans may not and are supposed not to carry out tasks beyond their capabilities and cannot simply play a role of God to perceive everything in the Universe.
1. 笛卡兒"我思故我在”. 2. David J. Chalmers "The Puzzle of Conscious Experience" in Scientific American, December 1995, pages 80-86. 3. The Holy Bible