Play it as a 3-minute lesson → short cards, one idea at a time
Choosing parents only works if their differences are heritable. Clones don't respond, and tight selection spends diversity.
Artificial selection is natural selection with a human choosing the parents. It can reshape a species fast, but only when the chosen differences are heritable, and it spends genetic diversity to do it.
Darwin used breeders' results to argue that selection could reshape a lineage. Broccoli, cabbage, kale, and Brussels sprouts all came from one wild mustard species, each selected for a different part of the plant. On the exam, artificial selection runs on the same logic as natural selection: no heritable variation, no response. Expect data where the chosen trait climbs while diversity or survival falls.
| Trap | Actually |
|---|---|
| Keep breeding the biggest plants and the next generation will be bigger. | Only if the size differences are heritable. Among clones, differences come from light and water, so the average won't move. |
| Breeds that look very different must be different species. | Broccoli, cabbage, and kale are one species and still cross. A new species needs reproductive isolation, not a new look. |
| Culling every affected animal will wipe out a harmful recessive allele. | Once the allele is rare, most copies sit in healthy carriers. Culling removes it slower and slower. Carrier testing works better. |
| Inserting a gene or raising the mutation rate counts as artificial selection. | Artificial selection only chooses who breeds. Genetic engineering and mutagenesis change DNA directly; they're different tools. |
Researchers start three lines of fruit flies from one lab population, all kept on the same food in the same room. Each generation, line Up breeds only the most active 10% of flies, line Down breeds only the least active 10%, and line Control breeds flies chosen at random. At generation 0, all three lines average 50 on an activity test. At generation 15, Up averages 78, Down 27, and Control 51. What do these results show, and why does the Control line matter?
Activity level has a heritable component, and choosing parents shifted it in both directions. The Control line shows the change came from selection, not from the lab conditions.
Selection moves a trait's average only when parents pass on their differences. Two lines splitting apart under identical conditions is strong evidence they did. The near miss is 'the flies adapted to the lab.' If that were true, the Control line would have changed too, and it stayed near 50.
Ten questions on Artificial Selection, each with a ten-second explanation. Free, no account.
Keeping only the heaviest chickens as parents each generation is which type of selection?
B — Favoring one extreme of a trait shifts the population's average toward that extreme over generations, which is directional selection. Stabilizing selection would favor chickens near the average weight, trimming both extremes instead of pushing the mean upward.
In artificial selection, what determines which individuals get to reproduce?
A — In artificial selection, people decide which organisms breed, based on traits they value, such as larger fruit or a calmer temperament. Predators and climate removing individuals describes natural selection, where the environment rather than a person does the choosing.
Breeding a line from only a few top parents for many generations usually does what to its genetic diversity?
B — When only a few individuals become parents, alleles carried by the rest are left out, and over generations many are lost, so the line becomes more genetically uniform. Mixing genes during reproduction reshuffles alleles already present but adds none, so it cannot restore what was lost.