Natural selection with no fitness function: mutation on versus off
There is no fitness function anywhere in this simulation. To check that selection was nonetheless doing real work, the same world was run twice per seed with only mutation toggled. Eight seeds out of eight moved the predicted gene in the predicted direction.
The question
Does natural selection, and not merely mutation, measurably shift the population mean of a gene in the direction its mechanism predicts, under an unmodified ecology with no fitness function anywhere in the code?
The hypothesis, written first
Pre-registered before interpretation: metabolic efficiency lowers basal energy cost with no other genome-level side effect at the time of the test. Under mutation on, organisms whose genome drifts toward higher efficiency should on average out-survive and out-reproduce those that drift lower, so the population mean should trend upward from the founder value of 0.5. Under mutation off the mean cannot move at all, because no variation exists to select among. That second condition is a mechanical control, not a finding.
Setup
- Ruleset
- Phase 2, superseded. The selection mechanism, which is the subject of the test, is unchanged.
- Seeds
- Seeds 1 to 8, both conditions per seed, 16 runs total.
- Duration
- 25,000 ticks per run.
What was measured
- Population mean of the metabolic efficiency gene at the end of each run.
- A contrast trait, body size, chosen because it had no predicted direction.
Result
Selection measurably moved the gene in the mechanically predicted direction, unanimously across 8 independent seeds, while an otherwise identical mutation-off condition could not move at all in any seed.
Limitations
- 8 seeds, not the 20 or more the project's own criterion suggested. A disclosed wall-clock trade-off, not a silent shortfall.
- Run on a small validation world, chosen for faster turnover. The result is about direction, not effect size at full scale.
- A sign test on 8 seeds is a coarse non-parametric check. The direction and the unanimity are the claim.
- The body size numbers reflect a mapping defect later fixed, and were not re-measured at this harness's scale afterwards.
Sources
Every number on this page comes from one of the following, all of which live in this project's own repository and are append-only records rather than summaries written after the fact.
- The project experiment log: EXP-0003, with EXP-0004 and EXP-0005 as the full-scale follow-ups
- The project decision record, section 39
Everything needed to check this claim is on this page already: the ruleset, the seeds, the duration, what was measured, the result, every limitation and the sources. Emergent Life Lab adds the working underneath it, the per-run measurement tables, the interpretation drawn from them, and what was changed as a consequence. See what Lab includes →