What does this equation mean?

which approaches a fixed value of 1 + a/b as t grows without bound, and $w_{\text{open}}(t) = 1 + a\,t^{\beta}$. for an exponent $\beta$ between 0 and 1, which keeps rising — more and more slowly, but without any asymptote — for every value of t . Wiser and colleagues derived the second form theoretically from a model combining clonal interference with diminishing-returns epistasis among beneficial mutations, and reported that across 50,000 generations of real data, “mean fitness appears to increase without bound, consistent with a power law” [ 2 ] . The decelerating rate that Lenski’s 1991 paper had already observed over the first 2,000 generations turns out to be compatible with no ceiling at all: a population’s fitness gains can keep shrinking, generation after generation, without the sum of those gains ever stopping. That is a specific, falsifiable claim about the shape of adaptation, not a synonym for “still improving.”