Each point is a colony's breeding value in 3 traits: resistance (x), productivity (y), gentleness (z). Every generation, the top fraction by selection pressure become parents; offspring average their parents' traits plus mutation noise.
select top (1 - pressure) fraction by weighted trait score
offspring_trait = avg(parentA, parentB) + N(0, mutation_rate)
line breeding: parents drawn from a narrow top slice -> diversity shrinks fast
hybridisation: parents drawn more broadly / crossed with an outside line -> diversity preserved
- Breeding method — line breeding concentrates desired traits quickly but narrows the gene pool; hybridisation keeps more diversity by mixing in less-related lines.
- Selection pressure — how strict the cut is each generation; higher pressure moves the population mean faster but shrinks diversity faster too.
- Mutation rate — random trait variation each generation; the raw material selection has to work with.
This is the real trade-off queen breeders manage: push resistance up too aggressively via tight line breeding and you risk inbreeding depression — losing vigor even as the target trait improves.