You guys are getting too philosophical or scientific and losing focus on what constitutes a living organism. You have to think not only about humans and animals but plants, bacteria, viruses and even non carbon based lifeforms. What is it we all have in common? The answer is that we are all forms of self sustained awareness. Humans have five senses that define our awareness. Some organisms share these senses while others have different ones, but it is all the same principle. And when we die our senses stop working because the foundation on which they exist breaks down. Thus, I don't believe in awareness after death, not unless there is a sixth or more sense beyond our current scientific understanding.
Now, if you want to figure out why we became aware that too is simple. Everything in the universe reacts to other things based on the laws of physics, whether it be gravity, electromagnetic fields or what not. And there is much more beyond our understanding. But our senses behave in the same way. They react to the physical conditions that register in our brains and use that info to sustain our mode of awareness. We are governed by the universal laws even if our set of senses are only temporary. its really simple. Thus our purpose of existence is to react with the forces at be just like everything else out there. We are just an expression of awareness. But when you add it all up I think we are part of a greater awareness, the great spirit if you will. It works on all levels.
Lets put it this way. In our body there are trillions of living organisms. White blood cells for example. They have their own life cycles and act independent of our consciouss will. And up until a hundred years ago we did not even know they existed. But they serve a purpose that is crucial to our own life cycle, our ability to sense and our capacity for self awareness, and they do so without even knowing we exist. Why cant it be the same for us? Why cant we be a minute part of a greater system? Everything works in the universe because there is system, the governing law of the cosmos if you will. We will never be able to grasp the full extent of it, but somehow I feel we are a part of everything by merely abiding by the same rules as everything else.