Living things change directions based on their needs.
Non-living things don't have needs.
Are you forgetting about plants, which typically don't move?
Living things can choose the direction in which it moves. Rocks can't choose direction. If a rock is impacted by another rock it will either move in the opposite direction of the impact force or it will break apart and no longer exist.
My assertion is simply that people are also guided by physical forces, just like rocks. If something jumps at you, you react to it. Action and reaction.
Living organsims maintain their identity over time even though the materials that it is made of come and go.
It's not that simple, I'm afraid. By some ways of measuring, most of our body is non-human. If an alien was observing us and classified us as "walking water-bags which transport a mixture of bacteria", and then they observed us later and saw that some of the cultures of bacteria were different due to a change in diet, would they still think we were the same organism?
You also can't speak about a brain in a bottle. That is pure fiction - not even science fiction. Brains need to be viewed as having a body connected to it. That body has needs and the brain, along with muscle, sense organs, and guts each serve their part in a functioning organism.
Sure, and the nerves that propagate information to the brain are the input to the equation. The brain reacts according to the way it's built to react to each kind of sensory stimulation, and then we produce output accordingly, like moving our legs to get away from a danger that we saw.
If you simplify the idea of an animal down to the single-celled level, the single cell is reacting to light it senses with its eyespot, and then waving its tail to go towards it. How is this different than a natural self-sustaining chemical reaction? The stimulus of light on one side of its body will cause it to react predictably, just like we can predict the results of mixing two chemicals.
Historically people have believed that we are special, that we choose how to react to things. I'm suggesting that this is a form of magical thinking, and that a human is just as predictable as a rock rolling downhill (assuming one is aware of all the factors that their brain is influenced by). This reduces consciousness to a form of input/output taking place on a chemical level.
