Selective Breeding
Selective Breeding
Selective breeding, also known as artificial selection, is a process used by humans to develop new organisms with desirable characteristics. This practice involves choosing two parents with beneficial phenotypic traits to reproduce, yielding offspring with those desired traits. Selective breeding has been a cornerstone of agriculture and animal husbandry for thousands of years, significantly impacting the development of plants and animals.
History of Selective Breeding
Humans have been modifying the traits of plant and animal species through selective breeding for millennia. More than 9,000 years ago in Mesoamerica, humans began selectively breeding teosinte plants that had greater numbers of kernels, eventually giving rise to corn (maize), one of the world's most widely distributed food crops. Similarly, cows were domesticated through selective breeding more than 10,000 years ago.
The term "artificial selection" was coined by Charles Darwin, who discussed how selective breeding had been successful in producing change over time in his 1859 book, On the Origin of Species. Darwin used artificial selection as an analogy to propose and explain the theory of natural selection, distinguishing the latter as a non-directed process driven by environmental factors.
Genetic Principles of Selective Breeding
Selective breeding results from the inheritance of gene-associated traits and changes in the frequencies with which desired traits occur in populations. This process alters gene frequencies in the population, making selective breeding a driver of evolution. The key to success in selective breeding is to identify the feature you want, only breed from the individuals that have that feature, and do not allow individuals with undesirable features to breed.
Applications of Selective Breeding
Selective breeding has a wide range of applications, including:
- Agriculture: Producing tastier fruits and vegetables, crops with greater resistance to pests, and higher yields.
- Animal Husbandry: Breeding larger animals for meat, dairy cows with higher milk production, and dogs with specific physical and behavioral traits.
- Horticulture: Developing ornamental plants with particular colors or shapes.
Examples in Agriculture
Humans created the vast majority of crop species by using traditional breeding practices on naturally occurring, wild plants. For example, high-yield varieties of wheat and rice were produced through selective breeding. Traditional breeding practices, although low-tech and simple to perform, have the practical outcome of modifying an organism's genetic information, thus producing new traits.
Examples in Animal Husbandry
Dog breeding is a prime example of artificial selection. Although all dogs are descendants of the wolf, the use of artificial selection has allowed humans to drastically alter the appearance of dogs. For centuries, dogs have been bred for various desired characteristics, leading to the creation of a wide range of breeds, from the tiny Chihuahua to the massive Great Dane.
Challenges and Ethical Considerations
While selective breeding can increase the prevalence of desirable traits, it can also lead to unintended consequences. For example, the highly specific traits that are selectively bred into dogs can come at a huge disadvantage to their health. The lack of genetic diversity within the gene pool can lead to hereditary health problems. For instance, bulldogs and other flat-faced breeds can suffer from breathing problems, while large dogs commonly suffer from bone tumors due to their excess body weight.