What does the dreaded "E" word mean, anyway

More complex factors may determine variation in some stages of the life cycle, but the basic directionality (evolution, to astronomers) does not alter, and predictability from natural law remains precise and complete:

   The great spread in luminosities and colors of giant, supergiant, and
   subgiant stars is also understood to result from evolutionary events. When
   a star leaves the main sequence, its future evolution is precisely
   determined by its mass, rate of rotation (or angular momentum), chemical
   composition, and whether or not it is a member of a close binary system.

In the most revealing verbal clue of all, the discourse of this particular scientific culture seems to shun the word "evolution" when historical sequences become too meandering, too nondirectional, or too complex to explain as simple consequences of controlling laws--even though the end result may be markedly different from the beginning state, thus illustrating significant change through time. For example, the same Britannica article on stellar evolution notes that one can often reach conclusions about the origin of a star or a planet from the relative abundance of chemical elements in its present composition.

Earth, however, has become so modified during its geological history that we cannot use this inferential method to reconstruct the initial state of our own planet. Because the current configuration of Earth's surface developed through complex contingencies and could not have been predicted from simple laws, this style of change apparently does not rank as evolution--but only, in astronomical parlance, as being "affected":

   The relative abundances of the chemical elements provide significant clues
   regarding their origin. The Earth's crust has been affected severely by
   erosion, fractionation, and other geologic events, so that its present
   varied composition offers few clues as to its early stages.

I don't mention these differences to lament, to complain, or to criticize astronomers in any way. After all, their use of "evolution" remains more faithful to etymology and the original English definition, whereas our Darwinian reconstruction has virtually reversed the original meaning. In this case, since neither side will or should give up its understanding of "evolution" (astronomers because they have retained an original and etymologically correct meaning, and evolutionists because their redefinition expresses the very heart of their central and revolutionary concept of life's history), our best solution lies simply in exposing the legitimate differences and explaining the good reasons behind the disparity in usage.

In this way, at least, we may avoid confusion and also the special frustration generated when prolonged wrangles arise from misunderstandings of words rather than from genuine disputes about things and causes in nature. We evolutionary biologists must remain especially sensitive to this issue, because we still face considerable opposition, based on conventional hopes and fears, to our insistence that life evolves in unpredictable directions, with no inherent goal. Since astronomical evolution upholds both contrary positions--predictability and directionality--evolutionary biologists need to emphasize their own distinctive meaning, especially since the general public feels much more comfortable with the astronomical sense and will therefore impose this more congenial definition upon the history of life if we do not clearly explain the logic, the evidence, and the sheer fascination of our challenging conclusion.