What is a theory in biology?

Dear group,Recently, I had an exchange with a member of this forum who, discussing intelligent design, said that there is no such thing as the theory of evolution. If I understand him correctly, he thinks that biologists, as opposed to other scientists (e.g., physcists) lack some essential elements of training in scientific method and, therefore, misunderstand the term "theory."In this regard, may I ask, what really is a theory in biology?Here is my thought on it (please note that I am a researcher-experimenter and, more recently, a university biology teacher but not an expert-professional in the scientific method, philosophy of science etc.). I understand theory in biology as an unusually interesting and daring hypothesis with a broad scope and interest to all biologists, regardless of their narrow field of study. Like any hypothesis, a theory is a human statement (or a set of statements) that is, essentially, a "guess" trying to explain certain natural phenomena. However, UNLIKE most hypotheses, a theory is a statement or a set of statements that provides an explanatory framework to *life* in general (while most hypotheses in biology are guesses trying to explain only certain manifestations of life).If this understanding of a theory is anywhere near truth, then the theory of biological evolution - which, essentially, states that life as we know it is being constantly diversified because of the constant action of factors like mutation, natural selection, genetic drift, gene flow, and other suchlike factors - is, actually, a true theory. So are such theory as the chromosomal theory of heredity or the cellular theory. On the other hand, hypotheses that are concerned with particular manifestations of life are not theories, even if they are extremely interesting and daring; for example, Burnet's hypothesis of clonal selection or Jerne's network hypothesis are not theories, because they do not address phenomena outside of just one manifestation of life (the ability of some life forms to mount immune responses).I will be very grateful for all your insights.Best wishes,Richard

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