5 Principles of Natural Selection

1. There is variation (genetic diversity) among individuals in the population.

2. Some traits are heritable

3. More offspring are produced than can survive

   1. There is some selective pressure causing offspring to die

4. Some trait will increase an individual’s chances to survive and reproduce

5. Traits that are passed down more often and therefore become more common are called adaptations

   1. Change in a species over time is called evolution

   2. A population of a species becoming a new species is called speciation

Adaptation

• Speed of adaptation depends on:

  • Rate of reproduction

  • Strength of the advantage

• Different types of adaptations

  • Structural

    • Physical traits like body shape or parts

  • Physiological

    • Automatic body processes that help with survival and/or reproduction

  • Behavioral

    • Organism’s inherited responses to its environment

    • Instincts- not voluntary

• Speciation

  • Caused by evolution, but not always the result of evolution

  • More likely when the population is isolated

  • Genetic drift

    • Happens when a population of a species can no longer reproduce and produce viable/fertile offspring

• “Survival of the fittest”

  • It’s about reproduction, not survival

  • Good enough is all you need- “fitter” as opposed to “fittest”

Other Outcomes

1. Extinction

   1. When every member of a species (or population- local extinction) has died.

   2. More likely when:

      1. Species has low or no diversity

      2. Species has a small population

      3. Species is very specialized

      4. Change is rapid and extreme

2. Migration

   1. When a species moves to a new area because of changing conditions

   2. Not seasonal

   3. More likely when:

      1. Change is slow and gradual

      2. Suitable habitats are connected or very close together

      3. Species is very mobile

Artificial Selection

• Also called selective breeding

• Humans act as selective pressure

  • Identify individuals with desirable traits

  • Only allow those individuals to reproduce

  • Over time, desirable traits become more common in the population

• Works much faster than natural selection

• Has a goal in mind

• Effects of artificial selection

  • Positive

    • Faster change in the population

    • Useful (to humans) traits develop

  • Negative

    • Loss of diversity in the population

    • Genetic weaknesses can become common

• Examples

  • Dog breeds

  • Agriculture

  • High yield grains

  • Pest-resistant strains

  • Milk cows