Final answer:
The notion that species evolve over generations through evolution and natural selection is classified as a theory. This is backed by extensive observations and testing in the scientific field. The term 'theory' in science context signifies a solid explanation, not a guess or hypothesis.
Step-by-step explanation:
The concept that species evolve over a series of generations through evolution and natural selection is considered a theory. In scientific terms, a theory is a well-substantiated explanation of some aspect of the natural world that is acquired through the scientific method, and repeatedly tested and confirmed through observation and experimentation. For example, the Theory of Evolution is supported by a wide range of observations throughout the fields of genetics, anatomy, ecology, animal behavior, paleontology, and others. However, it is important to note that in science, 'theory' does not signify a guess or a hypothesis, but a well-established paradigm that explains a certain phenomenon or a set of observations.
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