Mechanisms of Population Change

Mechanisms of Population Change

• Overview: The content covers key mechanisms of population change, including mutations, adaptations, natural selection, evolution, evidence for evolution, and modern evolutionary theories.

Variation and Adaptation

• Variation: Refers to visible differences among organisms. It can occur:

  • Interspecific Variation: Differences between different species (e.g., various species of fish, insects).

  • Intraspecific Variation: Differences within the same species (e.g., differences in hair color, eye color, height).

• Diversity vs. Variation:

  • Variation: Observable traits that differ among individuals.

  • Diversity: The number of different species present in a specific area.

Importance of Variation

• Variation helps with survival:

  • Caused by sexual reproduction leading to unique DNA combinations (50% from each parent).

  • Populations with genetic variation are more resilient to diseases.

Artificial Selection

• Definition: A process driven by humans selecting for desirable traits in organisms (e.g., breeding horses for strength, cows for milk production).

• Examples:

  • Selecting dogs for certain traits.

  • Genetically modified organisms (GMOs).

Natural Selection

• Definition: The process where traits become more common in a population due to environmental changes.

  • Traits that enhance survival are passed on, often summarized as "survival of the fittest."

• Example: An antelope with four legs is likely to survive better than one with three legs.

Adaptation

• Definition: Variations that improve an organism's chances of survival and are passed to offspring.

• Examples of Adaptations:

  • Physical Adaptations:

  • E.g., a giraffe's long neck for reaching high leaves, camouflage, webbed toes in aquatic animals.

  • Behavioral Adaptations:

  • Actions animals take to survive, such as migration and hibernation.

Summary of Adaptations

• Physical features help organisms survive.

• Camouflage helps animals blend into their environment, while mimicry confuses predators.

• Chemical defenses, such as venom or bad-smelling substances, protect against predation.

Mutations

• Definition: Changes in DNA that can lead to variation.

• Frequency: Mutations occur frequently and lead to genetic diversity.

• Types of Mutations:

  • Can be beneficial (leading to favorable adaptations) or harmful.

• Examples of Mutations:

  • Color blindness (often not harmful but still a mutation)

  • Sickle cell anemia: affects red blood cells but provides resistance to malaria.

Key Takeaways

• Natural selection and adaptations are interconnected; adaptations arise from variation and are enhanced through natural selection.

• Variation, adaptation, artificial selection, and natural selection are crucial for understanding how populations change over time.