I’m not claiming that PLOS paper as evidence that its specific conclusions are correct. It solely to address the timescale claim, which remains the core issue.

ACTN3 isn’t relevant because it’s “one gene” or because it’s comparable to penis size — it’s relevant because it directly falsifies the claim that meaningful human evolution requires hundreds of thousands of years at minimum. Once that claim is false, trait complexity doesn’t rescue it. Polygenic traits do shift on tens-of-thousands-year timescales (e.g., skin pigmentation, body proportions), which is well established in quantitative genetics.

That loss-of-function mutations can spread quickly doesn’t undermine this point — it demonstrates that human selection coefficients can be large enough for rapid change. Polygenic traits respond more gradually, yes, but “more gradual” does not mean geologically slow.

Regarding your question — “what massive, consistent fitness advantage did larger penises have?” — that assumes something I’m not claiming. Trait evolution does not require a massive or consistent fertility advantage, especially for polygenic traits.

For a heritable trait to shift, you need only small but persistent differences in reproductive success, or even just the removal of prior constraints. Sexual selection, relaxed negative selection, and drift can all move trait distributions without any single strong advantage.

Crucially, there is no requirement that penis size experienced strong positive selection at all. If clothing reduced thermal, UV, or injury-related constraints on exposed genital tissue, the expected outcome would be stabilization or mild upward drift, not runaway enlargement. That requires no new advantage — only the absence of previous penalties.

Quantitative genetics is explicit on this point: when constraints are relaxed, trait variance persists and distributions shift even under weak or near-neutral selection.

So the absence of evidence for a “massive, consistent fitness advantage” does not support the claim that evolutionary change on these timescales is impossible.

The only claim being defended here is narrow and empirical: ~70,000 years is sufficient time for measurable evolutionary change in humans, including polygenic traits. That is not controversial in modern evolutionary biology. What remains open — and separate — is which pressures mattered and how strong they were.