Perfect Life Selection Lab: Artificial Selection & Pleiotropy

Selection Index

Breeding Focus Balanced

Selection Intensity (survivors kept) 40%

Mutation Rate 1.0%

Auto-evolve (1 gen / 1.1s)

Population State

Generation 0

Mean Body Size

50%

Mean Speed

50%

Heterozygosity

100%

Inbreeding F

Size Speed Inbreeding F

How it works

Each organism carries 22 diploid loci that jointly influence two quantitative traits, Body Size and Speed, through additive polygenic effects — the same model quantitative geneticists use for real breeding programs:

Breeding value:  BV = Σ [(allele1 + allele2)/2] · effect_locus
Response to selection (breeder's equation):
  R = h² · S
  h² = heritability, S = selection differential
Genetic correlation (pleiotropy):
  effect_speed(i) = ρ·effect_size(i) + √(1-ρ²)·noise(i),  ρ ≈ -0.55

Because ρ is negative, the same loci that push Body Size up tend to push Speed down — a real antagonistic-pleiotropy trade-off, not a scripted penalty. Every generation the top fraction ranked by your selection index breed (Mendelian segregation: each parent contributes one randomly chosen allele per locus), loci mutate at your chosen rate, and the population's heterozygosity — 2p(1-p) averaged over loci — is tracked. As you push selection intensity harder, genetic variance and heterozygosity fall and the inbreeding coefficient F rises, showing the real biological cost of over-optimizing a "perfect" population: reduced genetic diversity and diminishing response to further selection.

Breeding Focus — the weight of Speed vs. Size in the selection index used to rank organisms each generation.
Selection Intensity — what fraction of the population is allowed to breed; lower = harsher culling, faster trait change, faster diversity loss.
Mutation Rate — per-allele chance of flipping each generation; the only source of new genetic variance once heterozygosity has been depleted.

Generation advanced

Larger = bigger Body Size Bluer = faster Speed

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