Student Success Guide on Biodiversity and Evolution

Student Success Guide: Chapter 12 - The Origin and Diversification of Life on Earth

Learning Objectives

• Define life.
• Outline the conditions and evidence that support how life on Earth was formed.
• Explain how to identify and distinguish between species.
• Describe the process for naming a species.
• Explain why some species are not easily defined.
• Compare and contrast the biological species concept and the morphological species concept.
• Describe the various processes of speciation.
• State the purpose of a phylogenetic tree and what it can demonstrate.
• Differentiate between analogous traits and homologous features.
• Compare and contrast microevolution and macroevolution.
• Explain how adaptive radiation and extinction impact evolution.
• Describe the current biodiversity found in the three domains.

I. Life on Earth Most Likely Originated from Non-Living Materials

A. Cells and Self-Replicating Systems

• Different theories suggest life originated in phases:
  • Phase 1: Early Earth's atmosphere was very different, lacking oxygen, crucial for today's organisms.
  • Chemical Reactions: Small carbon- and hydrogen-based molecules likely formed vital building blocks for life through laboratory experiments, revealing complex molecule creation.
• Phase 2: Life requires replication. Early life forms developed self-replicating molecules, though they lacked certain characteristics of modern life.
• Phase 3: Formation of membranes was essential for survival and function. Microspheres are simple membrane bound structures that mimic some cellular behavior.

II. Species Are the Basic Units of Biodiversity

A. Definition and Characteristics of Species

• A species is a group of organisms that can reproduce together.
• Biological species concept relies on reproductive isolation rather than appearance.
  • Reproductive isolation: Organisms' inability to interbreed under natural conditions reflects separate species.
• Barriers to Reproduction:
  1. Prezygotic barriers: Occur before fertilization (e.g., temporal isolation).
  2. Postzygotic barriers: Occur after fertilization (e.g., hybrid sterility).
• Limitations of the biological species concept may apply to certain organisms like bacteria and asexual species.

B. Species Not Always Easily Defined

• Instances where the biological species concept fails:
  1. Hybrid species.
  2. Vague morphological distinctions.
  3. Cryptic species (different species that appear identical).
  4. Morphological species concept compares physical traits, different from biological concepts.

III. Evolutionary Trees and Biodiversity

A. Phylogenetic Trees

• Phylogenetic tree displays evolutionary relationships; reflects shared ancestry.
• Nodes indicate speciation events. Trees cannot assess how advanced a group is, nor can they show closeness based solely on traits.
• DNA sequencing enhances phylogenetic tree constructions by revealing genetic relationships beyond physical features.

IV. Macroevolution and Biodiversity

A. Overview of Evolution

• Macroevolution: Evolution occurring above the species level, incorporating larger time scales.
• Microevolution: Small-scale changes within a population.
• Examples:
  • Gradual change: Slow evolution observable over generations.
  • Punctuated equilibrium: Rapid evolution following long periods of stability.

B. Adaptive Radiations and Extinctions

• Adaptive radiation: Rapid diversification in response to environmental changes or mass extinctions, such as the demise of dinosaurs prompting mammalian diversification.
• Extinction: Loss of species which can be categorized:
  • Background extinction: Normal rate of extinction due to environmental changes.
  • Mass extinction: Significant loss of species due to catastrophic events, such as the Great Dying.

V. Classification of Life: Three Domains

A. Overview of Domains

• Living organisms are divided into three domains, which emerged from the complexity of life:
  • Bacteria: Unicellular prokaryotes, diverse environments.
  • Archaea: Unicellular prokaryotes, often extremophiles.
  • Eukarya: Multicellular or unicellular eukaryotes (includes plants, animals, fungi, and protists).
• Horizontal gene transfer complicates the classification of organisms, especially in bacteria.
• Characteristics of Viruses: Debate over their living status due to lack of cellular structure and reliance on host organisms.

VI. Characteristics of the Domains

• Compare and contrast organisms across domains:
  • Bacteria: Prokaryotic; includes essential roles in ecosystems.
  • Archaea: Unique ribosomal RNA; adapted to extreme conditions.
  • Eukarya: Complex cells with organelles; significant ecological and functional diversity.

Testing & Application

1. Explore implications of a semi-permeable membrane on the definition of life.
2. Discuss whether different bowerbird types represent separate species under the biological concept.
3. Analyze speciation type following geographical separation of fish populations.
4. Evaluate adaptive radiation through the lens of punctuated equilibrium.
5. Differentiate homologous vs. analogous structures with examples from the animal kingdom.