Chapter 7 Darwinian Evolution

Natural Selection and Evolution

• Natural selection and evolution provide a framework for understanding life on Earth

• Emphasizes changes over time without addressing purpose or concepts beyond the physical

Historical Context

• Charles Darwin (1859)

  • Published On the Origin of Species by Means of Natural Selection

  • Introduced critical concepts:

    • Evolution

    • Natural selection

• Key ideas:

  • Individuals with advantageous variations are more likely to survive and reproduce

• Darwin's Background

  • Youthful interest in nature; disliked formal schooling

  • Extensive travels and observations (1831-1836)

  • Spent decades reading, analyzing specimens, and discussing ideas with peers

Early Concepts of Change

• Radical Shift

  • Pre-Darwin: belief in a young Earth with unrelated, unchanging species

• Fossil Discoveries (1700s)

  • Indicated an ancient Earth with changing species over time

• Jean-Baptiste Lamarck

  • Early idea of species adapting over time

  • Incorrect: believed traits acquired during an organism's life could be inherited

• Charles Lyell

  • Proposed the Earth changed gradually through slow processes (e.g., Grand Canyon formation)

Key Points from Darwin's Work

• Common Ancestry

  • Modern species descend from common ancestors

• Natural Selection as a Mechanism

  • Overproduction:

    • More individuals born than resources can support

  • Limited Resources:

    • Resources (food, water, shelter) remain constant

  • Conclusion: Competition

    • Not all individuals survive and reproduce due to limited resources

  • Variation:

    • No two individuals are identical

Core Concepts of Natural Selection and Evolution

• Natural Selection:

  • Best-suited individuals survive and reproduce

• Evolution:

  • Traits passed across generations lead to population changes over time

  • Populations evolve, not individuals

• Important Insights:

  • Natural selection affects heritable traits only

  • No predetermined goals in evolution; it is reactive to present environmental conditions

• Adaptation:

  • Accumulation of favorable traits over time

  • Artificial Selection:

    • Humans have influenced reproductive success (e.g., breeding)

Evidence Supporting Evolution

• Fossil Record:

  • Forms through organisms dying and becoming sedimentary rock

  • Shows an ordered life development from prokaryotes onward

• Transitional Forms:

  • Evidence of lineage changes

• Biogeography:

  • Study of species distribution

  • Geographic isolation influences species (e.g., marsupials in Australia)

• Genetic Evidence:

  • All life utilizes DNA as a genetic code

  • Bioinformatics:

    • Uses computational tools for genetic data analysis

    • Closely related species share similar DNA and proteins

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Population and Gene Pool

• Populations:

  • Units of evolution; capable of interbreeding

  • Example: Differences between island populations

• Gene Pool:

  • Total genetic makeup of a population

• Genetic Variation:

  • Arises from mutations and sexual reproduction

• Microevolution:

  • Gradual changes in gene pools across generations