Artificial selection occurs when humans choose which individuals breed, increasing desired heritable traits over generations in evolving populations in evolving populations.
Artificial selection occurs when humans deliberately choose crop plants or domesticated animals with desirable inherited traits to breed.
Choose a heritable target phenotype → select parents showing it → breed them → measure offspring → repeat selection over generations, increasing associated alleles.
| Case | Selection type and reason |
|---|---|
| Repeatedly breeding wheat plants with high grain yield | Artificial: humans deliberately choose breeders |
| Repeatedly breeding dairy cattle with high milk yield | Artificial: humans deliberately choose breeders |
| Antibiotic-resistant bacteria becoming common during antibiotic use | Natural: the antibiotic is a pressure, but humans do not choose individual bacteria to reproduce |
Strong repeated choices can change a population quickly but may narrow genetic diversity or bring correlated undesirable traits.
Artificial selection changes who reproduces; it is not direct DNA editing. An unintended evolutionary consequence of a human action is not automatically artificial selection.
HL D4.1 turns selection into measurable population genetics. A gene pool changes when allele frequencies shift. Hardy-Weinberg gives a no-evolution baseline; selection graphs, isolated populations, artificial selection, and resistance show how forces move populations away from that baseline.
HL population-genetics questions ask students to quantify or model evolution. The answer starts with the gene pool and allele frequencies, then uses the model or selection graph to decide whether the population is at equilibrium or being shifted by selection, mutation, migration, drift, artificial selection, or isolation.