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Artificial selection (1 of 5) Fish example

Image caption:
This population of fish exhibits variation in body size. Some have genes for large size and some have genes for small size. This represents genetic variation in the population.

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Artificial selection in the lab (1 of 2)
Guppy spots are largely genetically controlled. Spots that help the guppy blend in with its surroundings protect it from predation — but spots that make it stand out help it attract mates. In this experiment, guppies were raised in ponds that varied in the coarseness of gravel on the bottom. All ponds had predators. After fewer than 15 generations of selection, the markings of guppies in different ponds had substantially diverged as a result of natural selection. In the presence of predators, guppies evolved to blend in with their background.

Artificial selection in the lab (2 of 2)
The same experiment was performed in the same pond set-up, but without predators. After fewer than 15 generations of selection, the markings of guppies in different ponds had substantially diverged as a result of natural selection. In the presence of predators, guppies evolved to blend in with their background.

Artificial selection of corn
Plants and animals are domesticated through artificial selection, which works like natural selection does, but with humans instead of nature doing the selecting. Here, humans plant only the plump teosinte kernels — the plants that grow from those seeds carry more genes for plumpness, but they still vary in many ways. Over many generations of selection, the frequency of desirable gene variants increases in the population — and so does the quality of the crop.

Artificial selection (2 of 5) Fish example
When the population is fished, many of the largest fish are removed, so more of the small-bodied fish (and their small-bodied genes) remain.

Artificial selection (3 of 5) Fish example
The population reproduces. Each individual passes their genes on to their offspring — however, since there are more small-bodied parents, there are also more small-bodied offspring.

Artificial selection (4 of 5) Fish example
In the next generation, the population has evolved: average body size in the population is smaller than it used to be and small-bodied genes are more common than they used to be.

Artificial selection (5 of 5) Fish example
This downward trend in body size will continue so long as the largest fish are harvested and there is genetic variation in the population.