lec 9 flashcards

Introduction

• Theory of Evolution: Central theme in biology; based on genetic variation and environmental adaptation.

• Importance of evidence from various scientific fields.

Main Observations of the Theory of Evolution

• Variation in Traits

  • Individuals in a population exhibit variation in traits.

  • Essential for evolution as it provides diversity within a population.

• Heritability

  • Variation among individuals is heritable, meaning traits can be passed from parents to offspring.

  • Ensures continuation of advantageous traits.

• Survival and Reproduction

  • Not all progeny survive to reproduce.

  • Survival of the fittest: only those best suited to their environment reproduce successfully.

• Adaptation

  • Species appear to be best suited to their environment due to gradual adaptation.

  • Over time, adaptations result from natural selection.

• Geographical Variation

  • As geographical distance increases, variations in traits between populations also tend to increase.

Natural Selection

• Descent with modification explains how species evolve.

• Processes involved include:

  • Heritable variation among progeny.

  • Survival of the fittest: selected traits increase chances of survival and reproduction.

Common Ancestry

• Proposed by Darwin in "On the Tendency of Varieties to Depart Indefinitely from the Original Type" (1858).

• All life forms share a common ancestor, resulting in:

  • Diversity: Variation within populations through descent with modification.

  • Unity: Similarities among diverse life forms.

Evidence Supporting Evolution

• Speciation: Process where one species diverges into multiple new species due to existing variation and adaptation to new environments.

• Fossil Records: Support evolutionary history by showing transition forms and continuity of morphological changes.

• Molecular Homology:

  • Similar gene sequences across different species indicating common ancestry.

  • Example: Eye genes in various organisms show significant genetic and protein similarity to mouse genes.

• Functional and Structural Homology:

  • Functional homology: Similar functions in different organisms (e.g., cilia in Paramecium and human lungs).

  • Structural homology: Similar organization and structure (e.g., electron microscope views of various organisms).

• Developmental Homology: Similar embryonic structures across species (e.g., gill slits in vertebrates).

• Vestigial Organs:

  • Organs that have lost their original function (e.g., nictitating membrane in humans).

Conclusion

• The Theory of Evolution explains diverse life forms' unity through common ancestry and descent with modification.

• Multiple scientific evidence lines, including fossil records, genomic analyses, and anatomical vestiges, converge to support evolution.