Artificial Selection
Humans mimic natural selection by intentionally choosing which organisms reproduce, revealing how selection can rapidly shape populations.
Selection with a human agent
In natural selection, the environment (predators, climate, competitors, disease) determines which individuals survive and reproduce. In artificial selection, humans play that role directly: breeders choose which individuals mate based on desired traits - larger fruit, more milk, a docile temperament, a particular coat color. The underlying genetic mechanism is identical to natural selection: heritable variation is filtered by differential reproduction across generations.
Because humans can impose very strong, consistent selection pressure - far stronger and more directed than most natural pressures - artificial selection can produce dramatic phenotypic change surprisingly quickly, often within just a few dozen generations.
Classic examples
- All modern dog breeds, from Chihuahuas to Great Danes, descend from gray wolves through thousands of years of selection for behavior, size, and appearance.
- Brassica oleracea, a single wild mustard species, has been selectively bred into broccoli, cauliflower, cabbage, kale, and Brussels sprouts by selecting for different plant parts (flower buds, leaves, stems, lateral buds).
- Modern corn (maize) looks nothing like its ancestor teosinte, a grass with small, hard kernels - thousands of years of selection for kernel size and softness transformed it.
Why artificial selection matters as evidence for evolution
Darwin himself used the well-known success of pigeon breeders and farmers in reshaping domesticated species as a key argument for the plausibility of natural selection: if humans, working over mere decades, could reshape a species this dramatically, comparable change guided by nature over millions of years is entirely reasonable.
Artificial selection also reveals a tradeoff: selecting intensely for one trait (e.g., rapid growth in broiler chickens) can reduce genetic diversity and inadvertently produce weaknesses in other traits (e.g., skeletal or cardiovascular problems), illustrating that selection optimizes for the criteria being selected, not overall fitness in a natural environment.
Key terms
4
- Artificial selection
- Selective breeding by humans to encourage desired traits in domesticated organisms.
- Selective breeding
- Choosing parents with a desired trait to produce offspring more likely to have that trait.
- Standing genetic variation
- The heritable variation already present in a population, available for selection to act on.
- Domestication
- The process of adapting wild plants and animals for human use through selective breeding over generations.
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