Human Intelligence: 50,000 Years Is Plenty — A Breeder’s-Equation Reality Check

TL;DR

• Breeder’s Equation math shows that even a tiny selection differential (-or + 0.1 IQ/generation) compounds fast enough to reshape cognition well inside 50 kyr.
• Empirical data say selection on IQ is ~ ± 0.6–0.8 points / generation today, falsifying the “S ≈ 0” premise directly.
• Ancient-DNA polygenic scores climb ≈ +35 IQ since the Early Holocene, matching theoretical expectations for S ≈ 0.2.
• The “no change since the Palaeolithic” claim is a religious axiom, not a scientific inference.

1 Quotes & the Blank-Slate Catechism#

“There’s been no biological change in humans in 40,000 or 50,000 years. Everything we call culture and civilization we’ve built with the same body and brain.” — Stephen Jay Gould  [^oai1]

“Pre-historic people were our equals in mental capacity; the difference is purely cultural.” — David Deutsch, Within Reason podcast, 2025  ¹

Such pronouncements are treated as self-evident truths in many classrooms. Below I treat them as falsifiable hypotheses and run the numbers.

2 The Breeder’s Equation on a Beer-Coaster#

[ \Delta Z ;=; h^{2},S ]

• ΔZ – change per generation in the trait mean.
• h² – heritability (≈ 0.5 for IQ²).
• S – selection differential (mean of breeders – population).

2.1 Height sanity-check#

If tall fathers average 1 inch above the mean (S = 1″), ΔZ ≈ 0.8″/generation. Ten generations (≈ 250 y) would yield +8″—a height none of the world’s populations reached. So for height, Σ S over 50 kyr must hover near zero.

2.2 IQ thought-experiment#

Set S = +1 IQ (below test-retest error). With h² = 0.5, ΔZ = 0.5. After 10 generations: +5 IQ. After 400 generations (~10 ky): +200 IQ—clearly absurd. Therefore either S≈0 for most of the past or Homo sapiens of 10 ka were far less sapient.

3 Selection Now: Two Independent Lines#

Magnitude ≈ 1 in the relaxed selection regime of the late 20th C. Claiming S < 0.1 for every prehistoric generation is special pleading.

4 Selection Then: Ancient-DNA Signals#

Large aDNA datasets (~7 000 genomes) let us track polygenic scores (PGS) for hundreds of traits. Findings most relevant here:

• Cognitive PGS rose ~0.5 SD since 10 ka—≈ +35 IQ if linear scaling holds. ⁵
• Half of the twelve strongest Holocene sweeps involve cognition-linked traits (educational attainment, intracranial volume, etc.).
• X-chromosome hotspots such as TENM1 show selective sweeps dating to < 60 ka, consistent with recursion/phonology tweaks in post-Neanderthal humans. ⁶

Plugging S ≈ 0.2 into the Breeder’s Equation reproduces the +35 IQ trajectory neatly.

5 Objections—& Why They Fail#

6 Implications#

• Sapient Paradox resolved. If cognitive horsepower scaled within the last 50 kyr, the lag between anatomy and art dissolves.
• Self-domestication timeframe. Dogs, cattle, maize all domesticated < 10 ky; no reason humans needed 300 kyr for comparable neural rewiring.
• Ideological fallout. Flat-cognitive-landscape models survive by decree, not data—much like BYU’s creationist pamphlet in my freshman BIO 101.

7 Conclusion#

Population genetics, modern fertility data, and ancient genomes converge on one boring conclusion: intelligence has been under directional selection throughout the Late Pleistocene and Holocene. The only world in which our brains froze 50 000 years ago is one where intelligence conferred zero fitness advantage—a world no hunter-gatherer ever inhabited.

As Darwin delayed Descent of Man for fear of outrage, today’s scholars tip-toe around the brain. But the genome doesn’t care. The numbers are in; the blank slate is out.

FAQ#

Q1. If human intelligence evolved significantly in the last 50,000 years, why does the archaeological record show early symbolic behavior?
A. Early artifacts like ochre engraving (75,000 BCE) or shell beads show isolated instances of symbolic thinking, but widespread, complex symbolic culture (formal art, religion, permanent settlements) explodes only after the Ice Age. The breeder’s equation suggests cognitive capacity increased gradually through selection, with symbolic expression crossing a threshold when neural prerequisites reached critical mass – explaining the “Sapient Paradox” of delayed cultural complexity despite early anatomical modernity.

Q2. How can we be confident that IQ polygenic scores from ancient DNA reflect actual intelligence changes?
A. Polygenic scores aggregate hundreds of genetic variants associated with educational attainment and cognitive performance in modern populations. Their steady increase (~0.5 SD, or +35 IQ points) since the Early Holocene matches theoretical expectations from selection pressures. While PGS aren’t perfect proxies for intelligence, the magnitude and consistency across multiple cognitive traits strongly suggests directional selection for enhanced information processing capacity during the transition to complex societies.

Q3. If intelligence selection was so strong in recent millennia, why don’t we see obvious cognitive differences between ancient and modern humans?
A. If we had a time machine and could adopt a Paleolithic infant and raise them today, they would probably have cognitive deficits (less domesticated/intelligent).

Footnotes

Sources#

1. S.J. Gould quote in Has Human Evolution Stopped? [^oai1]
2. D. Deutsch & A. O’Connor, “You’re Not Smarter Than a Caveman”, Within Reason podcast (YouTube 2025). ¹
3. Hugh-Jones D. et al., 2024 selection scan – see footnote 3. ⁸
4. Skov L. et al., “Extraordinary selection on the human X chromosome…”, Cell 2023. ⁶
5. Piffer D. “Evolutionary Trends of Polygenic Scores in European Populations…”, Twin Res. 2023. ⁵