Mouse study finds human fitness loss <0.4% per generation
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- Michael Lynch wrote in 2010 that a substantial reduction in human fitness can be expected over the next few centuries in industrialized societies.
- IQ decline studies reported falling scores in the UK, Australia, Denmark, Sweden and Norway.
- Peter Keightley bred 55 mouse lines for 21 generations under relaxed selection, finding a fitness loss equivalent to less than 0.4% per generation in humans.
- Joanna Masel notes that natural selection still operates, with at least a third of conceptions ending in miscarriage.
- Joanna Masel argues that rare beneficial mutations can offset many slight harms, and simulations show higher mutation rates can speed beneficial mutations faster than harmful ones.
- Human mutation rate is relatively high, especially due to paternal sperm mutations accumulating over a man's reproductive lifespan.
- Climate change is highlighted as a settled science issue that deserves far more concern than potential genetic degeneration.
Why it matters: The negligible fitness loss means societies need not allocate resources to counter a supposed genetic decline, while ongoing natural selection still shapes human evolution through health interventions. Meanwhile, climate change remains a far‑greater, quantifiable threat requiring immediate action.
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