Topic 7.1-7.3 Part 1: Natural and Artificial Selection

Natural and Artificial Selection

Learning Objective

  • Introduce Evolution: Adaptations

    • Definition: Traits that help organisms survive and reproduce

    • Examples include:

    • Camouflage

    • Echolocation

    • Snake venom

Adaptations

  • Adaptations are characteristics that develop in response to environmental pressures to meet survival requirements of the environment.

Natural Selection

  • Definition: The process through which adaptations arise as a result of environmental survival pressures.

  • Key Points:

    • Only living organisms can possess adaptations; non-living entities have only physical attributes.

    • Natural selection leads to adaptations in populations over time.

Selective & Artificial Breeding

  • Definitions:

    • Species: A group of organisms that can breed together to produce fertile offspring.

    • Selective Breeding: The practice where animal/plant breeders select organisms with desired traits to reproduce.

    • Breeders maintain a controlled, guarded gene pool to preserve desirable traits.

    • Desired traits can be:

    • Observable traits (phenotype)

    • Behavioral traits

    • Selective breeding is synonymous with artificial selection.

Natural Variation within Populations

  • Natural selection acts upon inherited genetic variation within the same species.

  • Example of Variation: Leaf insects can display variations such as:

    • Long or short bodies

    • Fat or skinny legs

  • Important Distinction:

    • Variation is influenced by the environment, but only genetically determined variations will be passed on to the next generation.

    • For instance, rabbits with genetically long legs will pass this trait on, while a predator-inflicted scar will not endure across generations.

The Nature of Natural Selection

  • Populations exhibit variation, but the critical aspect of natural selection is based on heredity, not environmental influences.

  • Many offspring are produced, but only a fraction survive to reproduce, a concept known as reproductive success.

    • Example: Evolutionary arms race where prey and predators adapt in response to each other.

    • Scenario 1: Increased predators necessitates prey developing camouflage.

    • Scenario 2: Improved camouflage leads to a challenge for predators, requiring better eyesight adaptations.

    • Scenario 3: Enhanced predator eyesight results in the visibility of prey, creating a repetitive cycle.

  • Key Insight: Repeated selection in the same direction across generations is required to solidify an adaptation.

Mutations and Evolution

  • Mutations introduce new variations randomly into a population.

  • It is crucial to note that:

    • Individuals do not evolve; rather, populations evolve over time through natural selection.

Survival of the Fittest

  • Natural selection is often summarized as "survival of the fittest" leading to reproductive success.

    • Example: The fittest individuals survive and hence reproduce, allowing their traits to persist in the population.

  • Environmental changes can shift fitness requirements. A phenotype providing a survival advantage in one setting may become a liability if the environment changes.

Selective Pressure

  • Selective pressure refers to environmental factors that reduce reproductive success.

    • It influences individuals within populations to adapt in order to ensure survival and the passage of their traits.

  • Examples of selective pressure:

    • Predation

    • Climate conditions

    • Disease

Historical Context

  • Co-discoverers of natural selection: Charles Darwin and Alfred Russel Wallace

Differential Survival

  • Definition: Competition for limited resources leads to differences in survival, impacting reproductive success among individuals.