Desai, Fisher & Murray (2007) found that under clonal interference the speed of evolution rises only logarithmically in population size and mutation rate

"The speed of evolution and maintenance of variation in asexual populations" (Michael M. Desai, Daniel S. Fisher & Andrew W. Murray, Current Biology 17:5, 2007) analyzes what happens when a large asexual population generates beneficial mutations faster than any one of them can fix. Multiple favorable lineages then compete simultaneously — clonal interference — and most are lost even though they are advantageous, because a fitter competitor sweeps first. The consequence is a hard limit on how fast adaptation can proceed: "the speed of evolution increases only as the logarithm of the population size and the logarithm of the mutation rate."

Logarithmic dependence is a severe diminishing return. Multiplying the population by a factor of ten does not multiply the adaptation rate by ten; it adds a roughly constant increment. The extra individuals overwhelmingly supply mutations that interfere with, rather than accelerate, the fixation of the best variant. The result extends the Gerrish & Lenski (1998) clonal-interference lineage into an analytic scaling law.

This is the biology instance of the same brake economics found in claim-bloom-2020-ideas-are-getting-harder-to-find. It closes the loop on the population-as-engine story: the acceleration mechanism of claim-kremer-1993-technology-growth-proportional-to-population and claim-hawks-2007-human-adaptive-evolution-accelerated-recently — more agents, more variation, faster improvement — is not free in either domain. Beyond a point, scaling the generating population yields sub-linear returns, and the friction is not an economics artifact but a general property of populations generating variation. The cross-domain pattern is drawn together in observation-population-scaled-improvement-hits-a-sublinear-brake-across-domains.