Trevor,
It appears to be a post hoc excuse for an assumption (that something called "life" exists) that was made at the start, and then never sufficiently proven. For an entire science, I would call nothing short of a logical necessity sufficient ground for theory: building a science from appearances is lazy. (Natural selection, by the way, is logically necessary; plant cells are not.)
All science is build from appearances though, that is all we have to work with. For instance: there appears to be groups of organisms interacting in our environment, and they appear to have some common properties with each other, so we group these organisms into classification scheme called life, as that is how things appear to us.
2) What a biologist calls "life" does not appear to be identical with what common people and creationists call life (let alone Zen monks), so the argument between creationists and evolutionists about the origins of life is meaningless. Rarely do the two sides argue about the same thing.
How creationists typically conceive of life usually doesn’t match up with how things appear to us, usually they bring the supernatural into reality, which isn’t how things appear, so I would say a biologists definition of life is more sane and rational.
Creationists typically argue about fantastic supernatural ideas to make their egos feel secure, immortal, and all the rest of it. Biologists are simply trying to figure out how a section of reality appears to be functioning.
3) The process of natural selection has many uses outside of biology, yet is considered a biological theory. It is being held hostage. Natural selection should be categorized with other, similar, processes; from least to most efficient this list would contain physical collisions, natural selection, trial-and-error, artificial selection, and engineering.
I think the theory is only being held hostage by ignorant scientists who are strongly attached to their specialization and are afraid to lose what they identify with, any sane scientist would be able to see the truth of what you are saying here. I assume it is common knowledge for an elite of intellectuals that natural selection can be applied to many other areas of study besides biology. I have seen models of it used on the discovery channel for things like technological change, computer engineering and so on.
4) Life does not appear to be a consistent category; defining it by one appearance (for instance, the cell) is a step in the wrong direction. It should be defined by a logical necessity, as Newton did prior to applying his theoretical models to the world with a measurement.
It seems to me that Newton defined things first by how they appeared to him, this is how he came up with his theoretical models, and then the mathematical proofs came afterwards.
For instance: when the apple fell from the tree, Newton had an insight into gravity, as he was able to imagine that the earth had exerted more gravitational force on the apple than the apple did on the earth. And then he was able to imagine the earth spinning around the sun in an orbit due to the sun’s greater mass. So his first insights were based on imagining how things actually appeared based on smaller related observations, and then he used this knowledge to work out his mathematical proofs.
The truth is that when we define things, all we have to work with is the appearances that are available to our scope of perception at the time. And technology increases our scope of perception. For instance: In Plato’s day, he would have defined life based on the outward characteristics alone, as he didn’t have the technology to be aware of the cellular structure.
For instance: He would have said life consists of animals and plants, and what distinguishes them from other things is their ability to reproduce, their ability to take nourishment from the environment, their ability to grow into maturity from a more infantile state, and so on. He would have had no idea that they have a common cellular structure.
So to me the word ‘life’ is just a way of classifying common things. It is the same as mechanics classifying motor vehicles into groups such as cars, trucks, and motorcycles.