BIO 101 Final Exam Study Guide: Evolution, Speciation, and the History of Life

Chapter 22 – Natural Selection

Introduction to Evolution and Natural Selection

This chapter explores the foundational concepts of evolution, focusing on Charles Darwin's theory of natural selection and the evidence supporting evolutionary change. Understanding these principles is essential for grasping the unity and diversity of life.

• Charles Darwin: Developed the theory of evolution by natural selection, explaining how species change over time.

• Natural Selection (Definition): The process by which individuals with advantageous traits survive and reproduce more successfully, leading to the accumulation of those traits in the population.

• Evolution (Definition): Descent with modification; the change in the genetic composition of a population over generations.

• Unity and Diversity of Life: All organisms share common characteristics (unity) but also exhibit vast differences (diversity) due to evolutionary processes.

Historical Context and Key Figures

• Paleontology and Cuvier: Georges Cuvier founded paleontology and recognized extinction in the fossil record.

• James Hutton & Charles Lyell: Proposed that Earth's features developed gradually over long periods (uniformitarianism), influencing Darwin's thinking.

Key Concepts in Evolution

• Adaptations: Inherited traits that enhance survival and reproduction in a specific environment.

• Descent with Modification: The passing of traits from parent to offspring, with changes accumulating over generations.

• Artificial Selection: Humans selectively breed organisms for desired traits, demonstrating the power of selection.

Darwin’s Observations and Inferences

• Observation 1: Members of a population vary in their inherited traits.

• Observation 2: All species can produce more offspring than the environment can support.

• Inference 1: Individuals with advantageous traits leave more offspring.

• Inference 2: Over generations, favorable traits accumulate in the population.

Evidence for Evolution

• Allele Frequency: The proportion of a specific allele among all alleles in a population.

• Populations Evolve: Evolution occurs at the population level, not in individuals.

• Types of Data Supporting Evolution:

  • Direct Observations: Example: MRSA (antibiotic-resistant bacteria).

  • Homology: Similar structures due to shared ancestry (e.g., mammal forearm bones).

  • Vestigial Structures: Remnants of features that served a function in ancestors.

  • Convergent Evolution: Independent evolution of similar traits in unrelated lineages (e.g., wings in bats and insects).

  • Analogous Traits vs. Homologous Traits: Analogous traits arise from convergent evolution; homologous traits from common ancestry.

  • Biogeography: Geographic distribution of species provides evidence for evolution.

Chapter 23 – Evolution of Populations

Mechanisms of Evolution

This chapter examines how populations evolve through changes in allele frequencies, focusing on the mechanisms that drive evolutionary change.

• Four Mechanisms of Evolution:

  • Natural Selection

  • Genetic Drift

  • Gene Flow

  • Mutation

• Microevolution vs. Macroevolution: Microevolution refers to changes within populations; macroevolution involves larger-scale changes, such as the formation of new species.

• Genetic Variation: Differences in DNA among individuals; essential for evolution.

• Mutation and New Alleles: Mutations are the source of new genetic variation.

• Types of Mutations: Point mutations, insertions, deletions, duplications, etc.

• Sexual Reproduction: Increases genetic variation through recombination.

Hardy-Weinberg Principle

• Purpose: Measures whether a population is evolving by comparing observed and expected genotype frequencies.

• Equation:

  • $p^2 + 2pq + q^2 = 1$

  • $p + q = 1$

Genetic Drift and Gene Flow

• Genetic Drift: Random changes in allele frequencies, especially in small populations.

• Founder Effect: A few individuals start a new population; allele frequencies differ from the original population. Example: Colonization of an island.

• Bottleneck Effect: A sudden reduction in population size changes allele frequencies. Example: Northern elephant seals after hunting.

• Gene Flow: Movement of alleles between populations, reducing differences among populations.

Natural Selection and Types of Selection

• Relative Fitness: The contribution an individual makes to the gene pool relative to others.

• Directional Selection: Favors one extreme phenotype. Example: Larger beak size in finches during drought.

• Stabilizing Selection: Favors intermediate phenotypes. Example: Human birth weight.

• Disruptive Selection: Favors both extremes over intermediates.

• Adaptations: Traits that increase fitness in a given environment.

• Sexual Selection: Selection for traits that enhance mating success.

• Environmental Impacts: Changing environments can alter selective pressures.

Chapter 24 – Origin of Species

Speciation and the Biological Species Concept

This chapter discusses how new species arise and the mechanisms that maintain species boundaries.

• Speciation: The process by which one species splits into two or more species.

• Biological Species Concept: Species are groups of interbreeding natural populations that are reproductively isolated from other such groups.

Reproductive Isolation

• Prezygotic Barriers: Prevent mating or fertilization between species.

  • Habitat Isolation: Species live in different habitats. Example: Garter snakes in water vs. land.

  • Temporal Isolation: Species breed at different times. Example: Skunks breeding in different seasons.

  • Behavioral Isolation: Unique courtship behaviors. Example: Bird songs.

  • Mechanical Isolation: Morphological differences prevent mating. Example: Incompatible insect genitalia.

  • Gametic Isolation: Sperm and egg are incompatible. Example: Sea urchin gametes.

• Postzygotic Barriers: Prevent hybrid offspring from developing into viable, fertile adults.

  • Reduced Hybrid Viability: Hybrids do not develop properly. Example: Salamander hybrids.

  • Reduced Hybrid Fertility: Hybrids are sterile. Example: Mule (horse × donkey).

  • Hybrid Breakdown: Hybrids are fertile but their offspring are weak or sterile.

• Limitations of Biological Species Concept: Not applicable to asexual organisms or fossils.

Modes of Speciation

• Allopatric Speciation: Populations are geographically separated.

• Sympatric Speciation: Speciation occurs without geographic separation. Example: Cichlid fish in African lakes.

Hybrid Zones and Speciation Outcomes

• Hybrid Zones: Regions where different species meet and mate, producing hybrids.

• Hybrid Zones Over Time – Three Outcomes:

  • Reinforcement (strengthening reproductive barriers)

  • Fusion (weakening barriers, species merge)

  • Stability (continued production of hybrids)

• Punctuated Equilibria: Long periods of stability interrupted by brief periods of rapid change.

Chapter 25 – History of Life on Earth

Macroevolution and Early Earth

This chapter covers the broad patterns of evolution above the species level and the major events in the history of life.

• Macroevolution: Evolutionary change above the species level, including the origin of new groups and mass extinctions.

• Early Conditions on Earth: Earth’s early environment was suitable for the origin of life (e.g., presence of water, simple molecules).

Fossil Record and Dating

• Types of Fossils: Body fossils, trace fossils, and chemical fossils.

• What Does the Fossil Record Show? Reveals the existence, diversity, extinction, and change of organisms over time.

• Why Are Fossil Records Incomplete? Not all organisms fossilize; soft-bodied organisms are less likely to be preserved.

• What Types of Fossil Records Are Favored? Hard parts, widespread, abundant, and lived in sedimentary environments.

• How Are Fossils Dated? Relative dating (stratigraphy) and absolute dating (radiometric methods).

Geological Time Scale

• Eons and Eras: Major divisions of geological time (e.g., Hadean, Archaean, Proterozoic, Phanerozoic eons).

Key Events in the History of Life

• First Single-Celled Organisms and Stromatolites: Earliest evidence of life (~3.5 billion years ago).

• Photosynthesis and the Oxygen Revolution: Cyanobacteria produced oxygen, transforming Earth’s atmosphere.

• First Eukaryotes and Endosymbiosis: Eukaryotes arose via endosymbiosis (e.g., mitochondria and chloroplasts).

• Origin of Multicellularity: Multicellular organisms evolved from single-celled ancestors.

• Cambrian Explosion: Rapid diversification of animal life (~535 million years ago).

• Colonization of Land: Plants, fungi, arthropods, and tetrapods moved onto land.

• Plate Tectonics and Pangaea: Movement of continents influenced evolution and distribution of species.

Mass Extinctions and Adaptive Radiation

• Mass Extinctions: Large-scale extinctions that drastically reduce biodiversity.

  • Permian Mass Extinction: Largest extinction event (~252 million years ago).

  • Cretaceous Mass Extinction: Ended the age of dinosaurs (~66 million years ago).

  • Sixth Mass Extinction: Ongoing, largely due to human activity.

• Adaptive Radiation: Rapid evolution of diversely adapted species from a common ancestor, often following mass extinctions or colonization of new areas.