Artificial Selection (HL) (HL IB Biology)

• Artificial selection is the process by which humans choose organisms with desirable traits and selectively breed them together to enhance the expression of these desirable traits over time and over many generations
  • This practice is also known as selective breeding
• Humans have been selectively breeding organisms for thousands of years, long before scientists understood the genetics behind it
• Knowledge of the alleles that contribute to the expression of the desired traits are not required as individuals are selected by their phenotypes, and not their genotypes
• As the genetics is not always understood, breeders can accidentally enhance other traits that are genetically linked to the desirable trait
  • These other traits can sometimes negatively affect the organism's health

The process of artificial selection 

1. The population shows phenotypic variation - there are individuals with different phenotypes (i.e. different characteristics)
2. A breeder (the person carrying out the artificial selection) selects an individual with the desired phenotype
3. Another individual with the desired phenotype is selected. The two selected individuals should not be closely related to each other
4. The two selected individuals are bred together
5. The offspring produced reach maturity and are then tested for the desirable trait. Those that display the desired phenotype to the greatest degree are selected for further breeding
6. The process continues for many generations: the best individuals from the offspring are chosen for breeding until all offspring display the desirable trait

Selective breeding in animals

• Animals are selectively bred for various characteristics, including:
  • Cows, goats and sheep that produce a higher yield of milk or meat
  • Chickens that lay large eggs
  • Domestic dogs that have a gentle nature
  • Sheep with good quality wool
  • Horses with fine features and a very fast pace
• An example of an animal that has been selectively bred by humans in many ways to produce breeds with many different characteristics is the domestic dog, all breeds of which are descended from wolves

Selective breeding in dogs diagram

Selective breeding has produced many different breeds of domestic dog

Selective breeding in plants

• Selective breeding of plants takes place in the same way as selective breeding of animals
• Plants are selectively bred by humans for development of many characteristics, including:
  • Disease resistance in food crops
  • Increased crop yield
  • Hardiness to weather conditions (eg. drought tolerance)
  • Better tasting fruits
  • Large or unusual flowers
• An example of a plant that has been selectively bred in multiple ways is wild brassica, which has given rise to cauliflower, cabbage, broccoli, brussel sprouts, kale and kohlrabi

Selective breeding in plants diagram

An example of selective breeding in plants

What is the difference between natural and artificial selection?

• Artificial selection involves a deliberate choice of traits by humans whereas natural selection does not
• For example, the evolution of resistant bacteria from the overuse of antibiotics in humans is due to natural selection
  • Humans did not deliberately use antibiotics in order to produce resistant bacteria; it was an unintended consequence
• Natural selection results in an animal better adapted to their environment
• Artificial selection can result in animals poorly suited to their environment