Artificial Selection (College Board AP® Biology): Study Guide

Artificial selection

• Humans can influence the variation present in other species as follows:

  • individuals with desirable traits are chosen

  • these individuals are bred together

  • offspring from the cross with the desirable traits are chosen and bred together

  • this is repeated over many generations until the frequency of the desired characteristic increases

• This practice is also known as selective breeding

• Examples of artificial selection include:

  • increased milk yield from cattle

  • faster racehorses

  • disease-resistant crops

Convergent evolution

• Convergent evolution occurs when similar environmental selection pressures result in the evolution of similar phenotypic characteristics across unrelated species

  • These traits arise independently but serve the same functional purposes

• E.g. dolphins and sharks have similar adaptations due to convergent evolution

  • These are both groups of aquatic animals that share a similar body shape, but that belong to different classes

    • Dolphins are mammals and sharks are fish

  • Their streamlined body shapes evolved separately due to similar selective pressures acting in their aquatic environments

Artificial selection and convergent evolution

• Artificial selection occurs when humans actively select for specific traits in organisms; humans create the selective pressure

  • E.g. in food production farmers often apply selective pressures to increase agricultural efficiency and profit

• Over time these similar selective pressures can drive convergent evolution, causing similar phenotypic traits to arise in unrelated species or populations, e.g.:

  • maize (corn) and sorghum:

    • Artificial selection in different regions has resulted in similar traits, such as high yield and resistance to drought

  • tomatoes and peppers:

    • Selection for larger fruit sizes and vibrant colors has resulted in similar traits in these different species

  • cows, sheep, and goats:

    • Artificial selection for increased milk production in different species has independently resulted in similar physiological traits like larger udders and higher metabolic efficiency