BackBIO 101 Final Exam Study Guide: Evolution, Speciation, and the History of Life
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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): A 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.
Paleontology and Cuvier: Georges Cuvier founded paleontology, the study of fossils, and recognized extinction as a common event in Earth's history.
James Hutton & Charles Lyell: Proposed that Earth's features developed gradually over long periods, influencing Darwin's thinking about gradual biological change.
Adaptations: Inherited traits that enhance an organism's 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: The process by which humans select for desirable traits in organisms, 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 time, favorable traits accumulate in the population.
Allele Frequency: The proportion of a specific allele among all alleles in a population's gene pool.
Populations Evolve: Evolution occurs at the population level, not in individuals.
Evidence for Evolution
Direct Observations: Examples include the evolution of antibiotic resistance in MRSA bacteria.
Homology: Similarity in structure due to shared ancestry (e.g., mammal forearm bones).
Vestigial Structures: Remnants of features that served important functions in ancestors (e.g., human appendix).
Convergent Evolution: Independent evolution of similar features in different lineages (e.g., wings in bats and birds).
Analogous Traits vs. Homologous Traits: Analogous traits arise independently (not from a common ancestor), while homologous traits are inherited from a common ancestor.
Biogeography: The geographic distribution of species provides evidence for evolution (e.g., unique species on islands).
Chapter 23 – Evolution of Populations
Mechanisms of Evolution and Genetic Variation
This chapter examines how populations evolve through changes in allele frequencies, driven by several mechanisms. It also distinguishes between microevolution and macroevolution.
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 among individuals in a population, often due to mutations and sexual reproduction.
Mutation and New Alleles: Mutations are changes in DNA that create new alleles, providing raw material for evolution.
Types of Mutations: Point mutations, insertions, deletions, and chromosomal rearrangements.
Sexual Reproduction: Increases genetic variation by recombining alleles during meiosis and fertilization.
Hardy-Weinberg Principle
Purpose: Measures allele and genotype frequencies in a non-evolving population.
Equation:
Application: Used to determine if evolution is occurring in a population.
Mechanisms of Evolution in Detail
Genetic Drift: Random changes in allele frequencies, especially in small populations.
Founder Effect: A few individuals start a new population, leading to reduced genetic variation (e.g., colonization of an island).
Bottleneck Effect: A sudden reduction in population size due to a disaster, reducing genetic diversity (e.g., cheetah populations).
Gene Flow: Movement of alleles between populations, which can increase or decrease genetic variation.
Natural Selection and Adaptive Evolution: Favors traits that enhance survival and reproduction (adaptive evolution).
Relative Fitness: The contribution an individual makes to the gene pool relative to others.
Types of Selection:
Directional Selection: Favors one extreme phenotype (e.g., larger beak size in finches during drought).
Stabilizing Selection: Favors intermediate phenotypes (e.g., human birth weight).
Disruptive Selection: Favors both extreme phenotypes over intermediates.
Sexual Selection: Selection for traits that increase mating success (e.g., peacock feathers).
Environmental Impacts: Changing environments can alter selective pressures and evolutionary outcomes.
Chapter 24 – Origin of Species
Speciation and the Biological Species Concept
This chapter focuses on 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: Defines species as groups of interbreeding populations that are reproductively isolated from other groups.
Reproductive Isolation Mechanisms
Prezygotic Barriers: Prevent fertilization from occurring.
Habitat Isolation: Species live in different habitats (e.g., land vs. water).
Temporal Isolation: Species breed at different times (e.g., spring vs. fall).
Behavioral Isolation: Unique mating behaviors prevent interbreeding (e.g., bird songs).
Mechanical Isolation: Structural differences prevent mating (e.g., incompatible genitalia).
Gametic Isolation: Sperm and egg are incompatible (e.g., sea urchin gametes).
Postzygotic Barriers: Occur after fertilization, reducing hybrid viability or fertility.
Reduced Hybrid Viability: Hybrids fail to develop or are frail (e.g., salamander hybrids).
Reduced Hybrid Fertility: Hybrids are sterile (e.g., mule).
Hybrid Breakdown: Offspring of hybrids are weak or sterile.
Limitations of Biological Species Concept: Not applicable to asexual organisms or fossils.
Modes of Speciation
Allopatric Speciation: Occurs when populations are geographically separated.
Sympatric Speciation: Occurs without geographic separation (e.g., cichlid fish in African lakes).
Hybrid Zones: Regions where different species meet and mate, producing hybrids.
Hybrid Zones Over Time: Three possible outcomes:
Reinforcement (hybrids become less common)
Fusion (species merge)
Stability (hybrids continue to be produced)
Punctuated Equilibria: Evolutionary model suggesting species experience long periods of stability interrupted by brief periods of rapid change.
Chapter 25 – History of Life on Earth
Macroevolution and the Fossil Record
This chapter reviews the major events in the history of life, the fossil record, and the processes that have shaped biodiversity over time.
Macroevolution: Broad patterns of evolutionary change above the species level.
Early Earth Conditions: Earth’s early environment was suitable for the origin of life (e.g., presence of water, energy sources).
Types of Fossils: Body fossils (bones, shells), trace fossils (footprints), and chemical fossils.
Fossil Record Shows: Evidence of past life, evolutionary transitions, and extinction events.
Why Fossil Records Are Incomplete: Not all organisms fossilize well; soft-bodied organisms and those in certain environments are less likely to be preserved.
Favored Fossil Records: Organisms with hard parts, living in aquatic environments, and those buried rapidly are more likely to fossilize.
Dating Fossils: Relative dating (stratigraphy) and absolute dating (radiometric methods).
Major Events in the History of Life
Eons and Eras: The geologic time scale divides Earth’s history into eons (Hadean, Archaean, Proterozoic, Phanerozoic) and eras (Paleozoic, Mesozoic, Cenozoic).
First Single-Celled Organisms and Stromatolites: Stromatolites are layered structures formed by cyanobacteria, among the earliest evidence of life (~3.5 billion years ago).
Photosynthesis and the Oxygen Revolution: The evolution of photosynthetic organisms increased atmospheric oxygen, enabling aerobic life.
First Eukaryotes and Endosymbiosis: Eukaryotes originated via endosymbiosis, where one cell engulfed another (e.g., mitochondria and chloroplasts).
Origin of Multicellularity: Multicellular organisms evolved from single-celled ancestors.
Cambrian Explosion: A rapid diversification of animal life about 535-525 million years ago.
Colonization of Land: Plants, arthropods, and tetrapods were among the first to colonize terrestrial environments.
Plate Tectonics and Pangaea: Movement of Earth's plates has shaped the distribution of continents and species.
Mass Extinctions:
Permian Mass Extinction: Largest extinction event (~252 million years ago), eliminated ~96% of marine species.
Cretaceous Mass Extinction: Ended the age of dinosaurs (~66 million years ago), likely caused by an asteroid impact.
Sixth Mass Extinction: Ongoing, driven by human activities.
Adaptive Radiation: Rapid evolution of diverse species from a common ancestor, often following mass extinctions or colonization of new habitats.
