No really. What IS life? Not your life and my life, but life in general. What is the determining factor between life and non-life? And I'm not talking in a pro-choice / anti-abortion argument. I mean what constitutes something living. Near as I can see, life as I define it seems to be the point when someone or something realizes that it's alive. Think about it. There was a point where you weren't alive. Focus on memories you have from long ago. Think back as far as you can to your earliest memories. And try to push back just one more day into your past. Just one more memory further. Are you really alive before you remember?
Take for instance a video recording of you as a baby. Coo coo... yes very cute. But is that you? Think about you and everything that makes you... you. Focus on you, the you that's inside your body. Your mind, your heart, your soul. What ever you call it. Focus on that point. Take it in. Everything that is "you". Focus on it.
And watch that video. Watch that baby. Is it you? Can you find yourself in them? They become you, but you're nothing like them. And everything that they are has changed. Granted they become you, and you are identical genetically, but nothing that makes you ALIVE is the same. The voice in your head that's always with you. That's all that life is to you.
People are only able to comprehend based on their own experiences. Everyone knows the voice in their head. That is their life. Everyone else has one, but we can't begin to imagine how different they are from ourselves or how similar. I believe that you are alive from the furthest time in the past that you can currently remember and you will be until that voice stops speaking.
This leads perhaps to a lot of ethical life questions, but none of them are relevant. It also seems very self-centered, and it is, but it's not a bad thing. Self-centered is not selfish. Selfish is favoring yourself over others. Self-centered is a starting point for recognizing sentience.
Who are you? You're the voice in your head that's been there from the beginning and will be there until the end. The rest is irrelevant.
I think, therefore I am.