ideas-science-bio-theCharacterOfBiology

What makes biology different from other sciences? Well, it studies living things, which are a certain subset of all objects/phenomena which exist in the physical world.

But which things happen to exist in the physical world is an "accident". By defining "life", we can define the theory of biology as theory which is related to our definition of life, and then the distinction between the theory of biology and other sorts of theory is fundamental.

We here propose that the definition of life should be something like "homeostatic systems which evolve", where evolution is taken to be not just standard evolution (in which the genetic essence of an organism is fixed at birth), but some generalization roughly equivalent to, "A living organism is a member of a "natural" class of objects which exhibit homeostasis and which usually can reproduce, and which has associated genetic information which is passed on to children. The essential attributes defining the class are consequences of the genetic information in the organism, combined with the common features of the environments in which the organisms can maintain homeostatis and reproduce.".

This definition is inadequate in that the ill-defined notion of a "natural class" is used. The notions of "reproduction" and "homeostasis" are also ill-defined, but not as badly. Note that this definition does not accord with conventional usage in the respect that, under this definition, individual ants are not organisms, and ant colonies are.

This definition may exclude viruses from being alive, due to lack of homeostasis. However, one may regard the object commonly called a "virus" as merely a nonliving carrier of a virus's genetic information, and regard the thing commonly regarded as a "cell subverted by a virus" as the virus itself. A more radical (but in my view, better) way is to dismiss the implicit assumption that a single object can't be a component of two distinct organisms at once, and to regard the cell as both the body of the virus and part of the body of the host. This leaves room for interpreting vertically-propagating "viral" "junk DNA" as its own lifeform which co-inhabits a body along with the conventionally-recognized organism.

Thanks to Doug Rubino for this idea (although I don't want to put words into his mouth, I may have rephrased it in a way that he doesn't agree with).