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D4.1.15 (HL)—Artificial selection

Artificial selection occurs when humans choose which individuals breed, increasing desired heritable traits over generations in evolving populations in evolving populations.

Syllabus
First assessment 2025
Objective
D4.1.15
Level
HL

Artificial Selection Repeats Human Choice of Heritable Parents

HL only
  1. Choose a target phenotype that has heritable variation.
  2. Select parents showing the desired value.
  3. Breed them and measure offspring.
  4. Retain offspring with the strongest desired phenotype.
  5. Repeat across generations so associated alleles become more frequent.

Rapid improvement can reduce genetic diversity and bring linked harmful alleles or correlated traits along with the selected phenotype.

A maize sequence compares a small wild-type cob with progressively larger cobs produced by repeated selection across generations.

Artificial and Natural Selection Differ in Selector, Not in Inheritance

HL only
Feature Artificial selection Natural selection
source of reproductive advantage human breeder chooses parents environmental survival and mating pressures
variation required heritable variation heritable variation
population result chosen alleles change frequency alleles linked to higher fitness change frequency
guaranteed organismal benefit no; target serves human goal no universal benefit; adaptation is environment-specific

Antibiotic resistance is usually natural selection caused by a human-created pressure, not artificial selection: humans do not deliberately choose resistant bacteria as breeding parents.

Both processes reveal the same inheritance principle—repeated unequal reproduction changes a population over generations.

Population Genetics Measures How Selection and Other Forces Change Gene Pools

HL only

count allele copies in the gene pool → establish p and q → use Hardy–Weinberg as a no-change expectation → compare observed genotype or allele frequencies across generations → use phenotype, fitness and population evidence to identify selection or another evolutionary force

Pattern or action First model to examine
mean shifts toward one extreme directional selection
variance narrows around intermediate values stabilizing selection
both extremes rise and intermediates fall disruptive selection
observed genotypes differ from p²:2pq:q² one or more equilibrium assumptions may be violated
humans repeatedly choose parents artificial selection

Keep description, calculation and cause separate. A changed distribution describes an outcome; allele counts quantify evolution; causal claims require evidence about inheritance, survival, mating, migration, drift or deliberate breeding.

Concept essentials

  • Artificial selection is human-directed selective breeding.
  • Only heritable traits can respond reliably to artificial selection.
  • Repeated selection can increase desired traits but may reduce genetic diversity.