What does "working scientists" mean? Scientists who work?

But usually it it needless to say that a scientist always works...

Context:

Clearly, however, evolution has been the source of great discomfort in the religious community over the past 150 years,
and that resistance shows no signs of lessening. Yet believers would be well advised to look carefully at the overwhelming
weight of scientific data supporting this view of the relatedness of all living things, including ourselves. Given the strength of
the evidence, it is perplexing that so little progress in public ac-ceptance has occurred in the United States. Perhaps part of the problem relates to a simple misunderstanding of the word "the-ory." Critics are fond of pointing out that evolution is "only a theory," a statement that puzzles working scientists who are used to a different meaning of that word. My Funk & Wagnalls dictionary provides the following two alternative definitions for the word "theory": "(1) a speculative or conjectural view of something; (2) fundamental principles underlying a science, art, etc.: music theory, theory of equations."