Artificial selection is the process by which humans intentionally modify a species over successive generations by controlling which individuals reproduce. This intervention has been practiced for thousands of years, shaping the biological world to suit human needs. It is a powerful form of evolution fundamental to the development of agriculture and the domestication of animals, resulting in the wide variety of crops and livestock that form the foundation of global food systems today.
Selective Breeding
The most common and accurate alternative term for artificial selection is selective breeding. These two terms are essentially synonymous, referring to the purposeful choice of organisms with desirable characteristics to serve as parents for the next generation. Charles Darwin used the concept of artificial selection, particularly in pigeons, as an analogy to explain his theory of natural selection in his 1859 book, On the Origin of Species.
Other terms include “human-directed evolution” and “artificial breeding.” The core concept unifying all these names is the driving force behind the change: human preference and utility.
The Mechanism of Artificial Selection
The process of artificial selection begins with identifying a desirable, heritable trait within a population of plants or animals. Examples include increased milk production in cows, disease resistance in crops, or a more docile temperament.
Individuals exhibiting the trait most strongly are isolated and chosen as breeding stock. Controlled mating is facilitated between these selected individuals to combine their genetic material. This step is repeated over many generations, with breeders continually selecting only the offspring that display the trait to an even greater degree.
This method accelerates evolutionary change by concentrating the frequency of desired alleles within the gene pool. Simultaneously, unfavorable traits are actively removed from the breeding line. This focused pressure can transform a species, resulting in characteristics that would likely never arise naturally.
Comparing Artificial and Natural Selection
Both artificial and natural selection are mechanisms of evolution relying on heritable variation. The fundamental difference lies in the selective agent. In artificial selection, the human breeder serves as the agent; in natural selection, the environment (including predators, climate, and competition) determines which traits are advantageous.
The goal of selection also differs. Artificial selection is directed toward human utility or preference, such as higher yield or a specific aesthetic quality. Natural selection’s goal is reproductive fitness, ensuring individuals best suited for survival pass on their genes.
Artificial selection is generally much faster and more directed. Humans exert intense, focused pressure on a single trait, rapidly shifting characteristics in a few generations. Natural selection is a non-intentional process that unfolds over vast geological timescales, with pressures constantly changing.
Real-World Manifestations
The results of artificial selection are visible in nearly every domesticated species. The vast array of dog breeds, from the tiny Chihuahua to the massive Great Dane, all originated from the gray wolf through selective breeding for specific behaviors and physical traits. Breeds were developed to excel at specialized tasks like herding, hunting, or companionship.
In agriculture, the impact is equally profound. A classic example is the wild mustard plant, Brassica oleracea, which has been selectively bred to create a diversity of vegetables. By selecting for different parts of the plant, farmers developed modern cultivars.
Examples of Brassica oleracea Cultivars
Cabbage (by selecting for terminal leaf buds)
Broccoli (by selecting for flowers and stems)
Kale (by selecting for large leaves)
Kohlrabi (by selecting for the stem)
Brussels sprouts (by selecting for lateral leaf buds)