_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.