_Unit_7_Natural_Selection___Chp_22

Unit Overview

  • Unit 7: Natural Selection in AP Biology (Chapters 22/23)

Table of Contents

  • 7.1 - Natural Selection

  • 7.2 - Variations in Populations

  • 7.3 - Artificial Selection

  • 7.4 - Population Genetics

  • 7.5 - Hardy-Weinberg Equilibrium

  • 7.6 - Evidence of Evolution

  • 7.7 - Common Ancestry

  • 7.8 - Continuing Evolution

  • 7.9 - Phylogeny

  • 7.10 - Speciation

  • 7.11 - Extinction

  • 7.12 - Origin of Life on Earth

Quotes on Natural Selection

  • "Man selects only for his own good; Nature only for that of the being which she tends." - Charles Darwin.

7.1 Introduction to Natural Selection

  • Concept that organisms evolve through a mechanism known as natural selection, where traits enhancing survival are passed on.

Pre-Darwinian Views on Evolution

Historical Perspectives

  • Greeks and Fixed Species

    • Aristotle and Plato: Organisms viewed as perfectly adapted and unchanging.

  • Catastrophism (Cuvier)

    • Belief that fossils were remnants of catastrophic events; species could go extinct, but new species could not arise.

  • Gradualism (Hutton)

    • Changes in the Earth happen slowly, thus suggesting an ancient Earth exceeding the fixed species concept of only 6000 years.

  • Uniformitarianism (Lyell)

    • Earth’s processes observed today also were in operation in the past.

Early Theories of Evolution

  • Lamarck (1809)

    • Proposed mechanisms of evolution:

    1. Use and Disuse - Traits developed through use become enhanced.

    2. Acquired Characteristics - Modifications passed to offspring.

The Principles of Natural Selection

  • Natural Selection is the observable phenomenon that leads to evolution and defines how advantageous traits are selected.

    • Organisms with favorable traits are more likely to survive and reproduce.

  • Darwin's Contribution

    • Known as the father of modern evolutionary theory; introduced the concept of descent with modification in his book "The Origin of Species" (1859).

Key Factors in Natural Selection

  • Overproduction - More offspring than the environment can support.

  • Variation - Offspring show natural genetic differences.

  • Adaptation - Traits that improve survival and reproduction chances.

  • Competition - Competition for limited resources influences survival.

  • Differential Reproductive Success - Adaptive traits enhance survival rates, so over generations, these traits are more common.

Evolutionary Fitness

  • Defined by reproductive success; only those passing genes to the next generation are fit.

  • Populations evolve, not individuals, with gene pools representing the genetic diversity.

Biotic and Abiotic Influences

  • Environmental factors vary and can change adaptive values of phenotypes.

    • Biotic Factors: Living factors like predation and competition.

    • Abiotic Factors: Nonliving factors like sunlight and nutrient availability.

7.2 Types of Natural Selection

Selection Pressures

  • Environmental forces that affect reproductive success and can lead to evolutionary changes.

Three Ways of Natural Selection

  1. Directional Selection: Favors one end of the phenotypic spectrum, shifting frequencies toward that phenotype.

  2. Stabilizing Selection: Favors the average phenotype and reduces variability, selecting against extremes.

  3. Disruptive Selection: Favors both extreme phenotypes over the average.

Case Study: Sickle Cell Anemia

  • Caused by two alleles at a single locus; highlights heterozygote advantage by providing resistance to malaria in individuals with one mutated allele.

7.3 Artificial Selection

  • Process where humans select for desired traits in species to reproduce.

7.4 Evidence of Evolution

Lines of Evidence Supporting Evolution

  1. Fossil Record: Shows changes over time and evidence of extinct species.

  2. Homology: Similar structures indicating common ancestry.

  3. Analogy: Similar features in distantly related species due to convergent evolution.

  4. Transitional Species: Exhibiting features of multiple taxonomic groups, illustrating evolutionary transitions.

Dating Fossils

  • Fossils may be dated using sedimentary rock strata or radiometric methods, like Carbon-14 dating to determine absolute age.

Evolutionary Viewpoint of Taxonomy

  • Classification of life can show how species are related, with a hierarchy reflecting ancestry.

Molecular Biology in Evolution

  • Studying DNA and protein levels to understand molecular similarities and differences that inform evolutionary relationships.

Practice Free Response Questions

7.1 FRQ

  • Discuss changes in the finch population in response to environmental factors.

7.2 FRQ

  • Address genetic variation and its role in evolutionary processes.

7.3 FRQ

  • Consider biological risks of genetically modified crops and mitigation strategies.

7.6 FRQ

  • Justify claims regarding glycolysis as a pathway common to all life.