Part of the problem with conclusively 'proving' his thesis (vs. (say) a similar hypothesis dealing with fruit flies or bacteria) is the lack of extensive generational data for such a slowly reproducing species as ours is. Given the time it takes humans to currently reproduce (over 20 years on average) it is difficult to measure real selection taking place over the long term. Additionally, what may be true for humans in one part of the world, may not be true everywhere (or anywhere) else. Wills uses this last point to claim that we evolve not just by moving as a species in a particular direction (i.e. bigger feet, smaller chins, etc.) but we also 'evolve' by mixing our sometimes diverse DNA which has, in some cases, been kept separate for thousands of years.

The prose is never dull. Wills sheds new light on several older topics (like sickle cell anemia and the Neandertals) and he brings up some of the most cutting edge topics in various scientific fields like genetics. I've found that authors tend to reference books and articles that are on average five to ten years old. Not so with Wills. Nearly every study and article used or described in the text is from the mid-1990s with numerous selections from 1998 (the same year Children of Prometheus was published).

The Bell Curve is critiqued throughout the book. Although the critique is warranted, and Wills' arguments appear valid or at least plausible, it forced Wills to not delve into some of the data as extensively as a book on this subject probably should. Since humans now stand at the top of the food chain and face natural selection mostly from genetic defects and microorganism-related factors (instead of the usually thought of predator-prey selection), a more thorough analysis of the major causes of the choice to reproduce for a conscious species is needed. For instance, careful examination of the cultures, religions, and income levels that produce offspring in (much) higher than average numbers will tell us much more about current human evolution than a genetic mutation which affects only a minuscule percentage of the population and will take hundreds or thousands of generations to have a substantial impact will. Even if this isn't key to what we usually think of as 'natural selection', birth control is certainly key to the way Wills is describing evolution. Wills states (p. 252) that "there is no reason to suppose that selection for increased intellectual capacity in our species has slackened". However, if increased intellectual capacity in our current and future cultures really means that the recipients of such produce fewer children (due to the intellectual awareness of things like the problems excessive human population create) then the selection isn't heading in the direction Wills implies.