BiologyExam code: 4BI1
Selective Breeding
Use of Biological Resources
Selective breeding and natural selection both work by the same underlying mechanism (differences in reproduction between individuals with different traits), but they differ in important ways:
| Feature | Natural selection | Selective breeding (artificial selection) |
|---|---|---|
| What decides which individuals reproduce? | The environment (predators, competition, disease, weather) | Humans decide which individuals to breed |
| What traits get favoured? | Traits that help the organism survive and reproduce in its environment | Traits that humans find useful (more food, better appearance, etc.) |
| Are favoured traits always good for the organism? | Yes, in the current environment | No. Many selectively-bred traits would harm the organism if it had to survive in the wild. A modern broiler chicken cannot fly; modern dairy cows cannot produce enough milk to feed their own calves; bulldogs struggle to breathe due to their flat faces |
| Speed | Slow (thousands or millions of years for big changes) | Fast (decades or centuries for big changes, because every generation is intensely selected) |
| Source of new alleles | Random mutations | Random mutations (plus crossing different existing breeds) |
| Does it produce new species? | Yes, over enough time | Not usually. The breeder usually wants offspring to still be the same species and able to interbreed with the rest of the population |
The key idea: in natural selection, the environment chooses. In artificial selection, humans choose. Otherwise the genetic mechanism is the same.