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BLG144_Week 1_Jan 13

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BLG144_Week 1_Jan 13

Chapter Overview

  • Subject: Biology II: Evolution by Natural Selection

  • Instructor: Dr. Tarushika Vasanthan

  • Department: Chemistry & Biology

The Pattern of Evolution

  • Darwin's Definition of Evolution:

    • Descent with modification: Change over time leads to modern species from ancestral species.

    • Predictions of Natural Selection:

      1. Species change over time.

      2. Species are related through common ancestry.

Evidence for Change Through Time

  • Fossils: Traces of organisms from the past constitute the fossil record.

The Vastness of Geologic Time

  • Fossil Organization:

    • Fossils organized by relative age in sedimentary rocks.

    • Younger layers sit atop older layers.

  • Geologic Time Scale: Divided into eons, eras, periods, and epochs, indicating the Earth is over 6000 years old.

  • Absolute Dating: Employs radioactive decay to assign precise ages.

Extinction and Species Dynamics

  • Extinction Evidence:

    • Fossils provide evidence for extinct species; species are dynamic and change over time.

    • Over 99% of all species are extinct.

    • Extinctions have occurred continuously throughout Earth's history.

Transitional Features

  • Law of Succession: Similarity between fossil and living species supports species change over time.

  • Transitional Features:

    • Traits in fossils that are intermediate between ancestral and derived species, strong evidence of evolutionary change.

    • Example: Gradual transition from aquatic fins to terrestrial limbs.

Vestigial Traits

  • Definition: Reduced or incompletely developed structures that have no or reduced function.

  • Significance: Inconsistent with special creation; evidence species have changed over time.

Contemporary Examples of Evolution

  • Documented changes:

    • Bacteria evolving drug resistance.

    • Insects developing pesticide resistance.

    • Plant adaptation to herbicides and climate-related changes.

  • Evolution continues in real-time.

Descent from a Common Ancestor

  • Evidence Against Immutability: Fossil records and current species indicate relatedness.

Geographic Similarities and Evolution

  • Island Species: Striking similarities among species in the same geographic area.

  • Mockingbirds' Example: Darwin's hypothesis of common ancestry supported by DNA analyses.

  • Phylogenetic Tree: Illustrates ancestor-descendant relationships.

Homology as Evidence

  • Homology Defined: Similarity in species descended from a common ancestor, studied at three levels:

    1. Genetic

    2. Developmental

    3. Structural

Genetic Homology

  • Similarity in DNA or protein sequences (e.g., eyeless gene in fruit flies vs. Aniridia gene in humans).

Developmental Homology

  • Similar embryos across species (e.g., tails and gill pouches in various vertebrates).

Structural Homology

  • Similar adult structures (e.g., common limb bone arrangement in vertebrates).

Experimental Evidence for Homology

  • Hypotheses can be tested, such as gene transfer experiments leading to functional changes in different organisms.

Evolution Predictions

  • Non-static Nature of Species:

    • Fossil records indicate species change over time; transitional and vestigial traits are common.

    • Species Relatedness: Geographic similarities and homologous traits exist at genetic, developmental, and structural levels.

Internal Consistency in Evolution

  • Consistency of data from independent sources supports evolutionary theory (e.g., cetacean evolution).

Evidence from Multiple Sources

  • Relative and absolute dating consistently supports evolutionary trends.

  • DNA analysis strengthens the close relationship between hippos and cetaceans.

Understanding Evolution's Constraints

  • **Misconceptions about Natural Selection: **

    • Individuals do not change; populations evolve.

    • Natural selection is not goal-directed and does not result in "higher" organisms.

Constraints in Evolution

  • Fitness Trade-Offs: Adaptations come at a cost; traits may be compromised for efficiency.

  • Genetic Constraining and Historical Constraints: Traits evolve from pre-existing structures; adaptive evolution is influenced by historical factors.

Key Learning Objectives

  • Define evolution, fitness, and adaptation biologically.

  • Assess Darwin's postulates and apply examples in real scenarios.