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.