From Wiki, “a tautology is a statement containing more than one sub-statement, that is true regardless of the truth values of its parts—for example, the statement "Either all crows are black, or not all of them are," is a tautology, because it is true no matter what color crows are.

Also noted in Wiki, “A circular definition is one that assumes a prior understanding of the term being defined—for instance, we can define "oak" as a tree which has catkins and grows from an acorn, and then define "acorn" as the nut produced by an oak tree . . the definition is fairly useless.”

Natural selection is essentilly “survival of the fittest,” so long as “fitness” means the reproductive success of a genotype (and I suppose also with the implicit understanding that parlaying “survival of the fittest” into a “survival of the fittest” social Darwinism is obviously taboo).

Over the years I’ve read many, many comprehensive explanations of natural selection (and all the related terminology) by many “experts,” and the circularity and/or tautological aspects are unavoidable—which is fine, but let’s have a little intellectual rigor and honesty, and/or let’s call an acorn an acorn.

As I’ve noted elsewhere, Russell & Whitehead, at the beginning of the 20th century, attempted to establish that “math is tautology” in, among other things, their Principia Mathematica (ca. 1910), but their wet dream got a wakeup call from, among other things, Godel's Incompleteness Theorem (ca. 1930).

So the objective truth of mathematics is neither circular nor a tautology, and neither is real science—e.g., Newton’s laws of motion & gravity and/or Einstein’s general relativity equations are not tautologies, but rather provide us with equations and utilize objective mathematical truths to give us a noncircular view of how things actually work—and b/c they aren’t circular/tautological, they actually are falsifiable, and that is why it later could be shown that in fact Newton’s law of gravity was incomplete and that Einstein’s general relativity provided us with a more complete/realistic understanding and picture of how the universe actually works.

All that being said, I’d nevertheless agree that as surely as acorn trees come from acorn nuts, natural selection happens . . . although, frankly, if anyone thinks that tells us much, well, I’d say they’re nuts.