Artificial Selection

Summary

Humans breed organisms with desired traits, creating crops and dog breeds from wild ancestors.

In depth

Humans choose which individuals breed. Over thousands of years, wild mustard became cabbage, broccoli, kale and cauliflower; wolves became dog breeds. Darwin used it as an analogy for natural selection.

It can reduce diversity and cause health problems, such as breathing difficulties in bulldogs.

Darwin opened the Origin with domestic pigeons, with breeds as different as pouters and tumblers all descended from the rock dove. Experiments such as Illinois long-term corn selection, which raised oil content over 100 generations, show that selection keeps finding variation. The Russian fox farm experiment selected for tameness and produced floppy ears and coat patches within decades, as a by-product, demonstrating the domestication syndrome.

Artificial selection can reduce diversity and lead to health problems: pugs have breathing issues, and dairy cattle fertility declined. Modern breeding uses genomic selection to predict breeding value from DNA markers.

Example: teosinte, a grass with few hard kernels, became maize through selection by Mexican farmers over about 9000 years, involving changes in a few genes such as tb1.