(3) Unit 7 Topics 1 2 and 3 Packet

Overview of Unit Seven

• Focus on Topics One, Two, and Three: Natural Selection and Artificial Selection.

• Students generally grasp concepts easily except for phrasing related to natural selection, which is critical for AP exam success.

Natural Selection

• Definition: A process where organisms with advantageous traits survive and reproduce at higher rates than those without.

• Charles Darwin's Quote: "Natural selection is scrutinizing variations, preserving the good and rejecting the bad over time."

  • Evolution occurs slowly and is visible over long geological periods.

Key Concepts

• Biotic and Abiotic Factors: Influence trait selection for survival and reproduction.

• Evolution's Rate: Changes occur over long periods, not day-to-day.

• Support and Criticism of Darwin: While many of Darwin's ideas are well-supported, not all are accepted universally.

Background of Charles Darwin

• An English naturalist known for his research in the Galapagos Islands.

• Biogeography: Study of species' geographic distribution.

• Observed finches to understand species diversification from a single ancestor inhabiting the South American mainland.

Features of Darwin's Finches

• Variations in beak shape suited for different food sources.

• Inquiry into how traits (like beak shape) evolved in isolated environments.

True/False Game on Natural Selection

• Statements Analyzed:

  1. "Natural selection gives organisms what they need to survive."

     • False: Natural selection does not provide needs; it preserves advantageous traits based on genetic variations.

  2. "Natural selection acts for the good of a species."

     • False: Natural selection acts on traits that may or may not be beneficial to the long-term survival of the species. (Example: Predatory traits leading to extinction).

  3. "Natural selection is a process involving organisms trying to adapt to their surroundings."

     • False: Adaptations occur via genetic variations, not through conscious attempts by organisms.

  4. "Survival of the fittest refers to the strongest, healthiest, fastest organisms."

     • False: "Fittest" refers to those that can survive and reproduce, not necessarily the strongest.

Evolution vs. Natural Selection

• Evolution: Defined as change in the genetic makeup of a population over time (descent with modification).

• Natural Selection: Mechanism by which evolution occurs based on heritable traits leading to differential survival and reproduction.

• Fitness: Describes an organism's ability to survive and reproduce successfully.

• Selection pressures may change due to environmental changes, impacting which traits are advantageous.

• Populations Evolve, Not Individuals: Evolution occurs over generations, while individuals undergo mutation.

Artificial Selection

• Definition: The selective breeding of domesticated plants and animals to encourage desirable traits.

• Example: Mendel's breeding of pea plants for specific traits.

• Differences from Natural Selection:

  • Natural Selection: Nature selects advantageous traits for survival.

  • Artificial Selection: Humans select traits based on personal preferences, often neglecting natural survival instincts.

Summary of Darwin's Theories

• Descent with Modification: Heritable traits can change from generation to generation, leading to evolution.

• Observation Summary:

  1. Traits are heritable; adaptations can be passed on.

  2. More offspring are produced than can survive, leading to competition for limited resources.

• Example: Arctic fox and camel, showcasing adaptations enhancing survival.

Common Misunderstandings and Clarifications

• Misunderstanding the implications of weight loss as evolution or adaptation.

• Emphasizing that weight change due to environmental conditions does not constitute genetic evolution.

Practice Scenario: Pacas Population

• Scenario analysis indicates that weight loss due to food shortages does not reflect descent with modification since no genetic changes occurred, only temporary environmental effects.