AP® Biology · Unit 7 · Topic 7.3
Artificial Selection
Artificial selection is humans choosing which organisms reproduce based on traits they want, shifting a population's trait distribution over generations the same way natural selection does, just with a human picking the winners instead of the environment.
A chihuahua and a great dane look nothing alike, but they're the same species because both descend from wolves through thousands of years of humans choosing which dogs bred with which. That's artificial selection: pick the individuals with the trait you want, breed them together, repeat every generation. The trait doesn't have to exist in extreme form at the start. Breeders just need some heritable variation to work with, then they exaggerate it generation after generation. Wild mustard plant is the classic case: breeders who kept selecting plants with the largest leaves eventually got kale. Breeders who selected for the biggest flower buds got broccoli. Breeders who selected for compact terminal buds got cabbage. Same ancestral species, three different body parts pushed to extremes, three different crops.
Run this process for decades on a crop and the population's genetic diversity drops. Every generation, only the individuals with the desired trait get to reproduce, so alleles linked to unwanted traits get weeded out along with the ones actually being selected against. The result is a crop that's highly uniform and often more vulnerable to disease or environmental change, because the genetic backup that diversity provides has been bred away.
The reason this all connects back to natural selection is that the underlying mechanism never changes: individuals with certain heritable traits reproduce more than others, so the population's trait distribution shifts over time. Natural selection and artificial selection are the same process wearing different hats. In the wild, survival and environmental pressures decide who reproduces. On a farm, a breeder's clipboard decides. Either way, differential reproduction of heritable traits is doing the work.
Key terms
- Artificial selection
- Humans choosing which individuals reproduce based on desired heritable traits, shifting a population's traits over generations.
- Differential reproduction
- The pattern where individuals with certain traits produce more offspring than individuals without them.
- Heritable variation
- Differences between individuals that can be passed to offspring, the raw material selection acts on.
- Cultivar
- A plant variety produced through selective breeding rather than through natural processes alone.
- Genetic diversity
- The variety of alleles present in a population, often reduced by generations of selecting for one trait.
Watch it explained
- How it worksHow did broccoli, kale, and cabbage all get bred out of one wild mustard plant?
- How it worksWalk me through breeders picking parents each generation and the trait mean shifting.
- Going furtherWhat happens to genetic diversity in a crop after decades of selective breeding?
- Common mistakeWhy isn't artificial selection a fundamentally different process from natural selection?
Check yourself
End of topic.