BackBIO 101 Final Exam Study Guide: Evolution, Speciation, and the History of Life
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Chapter 22 – Natural Selection
Introduction to Natural Selection and Evolution
Natural selection is a central mechanism of evolution, first described by Charles Darwin. This chapter explores the evidence for evolution, the process of natural selection, and 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 living organisms share common characteristics (unity) but also display a wide variety of forms and functions (diversity).
Historical Context and Evidence
Paleontology and Cuvier: Georges Cuvier founded paleontology, the study of fossils, and recognized extinction as a common event in Earth's history.
James Hutton and Charles Lyell: Proposed that geological processes occur gradually over long periods, influencing Darwin's thinking about gradual biological change.
Key Concepts in Evolution
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, such as crops or domesticated animals.
Darwin’s Observations and Inferences
Observation 1: Members of a population often vary in their inherited traits.
Observation 2: All species can produce more offspring than the environment can support, and many offspring fail to survive and reproduce.
Inference 1: Individuals whose inherited traits give them a higher probability of surviving and reproducing tend to leave more offspring.
Inference 2: This unequal ability to survive and reproduce leads to the accumulation of favorable traits over generations.
Population Genetics and 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) evolving resistance.
Homology: Similarity in structure due to shared ancestry (e.g., mammal forearm bones).
Vestigial Structures: Remnants of features that served a function 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, homologous traits are inherited from a common ancestor.
Biogeography: The geographic distribution of species provides evidence for evolution.
Chapter 23 – Evolution of Populations
Mechanisms of Evolution and Genetic Variation
This chapter focuses on how populations evolve through changes in allele frequencies, the sources of genetic variation, and the mechanisms driving evolutionary change.
Four Mechanisms of Evolution:
Natural Selection
Genetic Drift
Gene Flow
Mutation
Microevolution vs. Macroevolution: Microevolution refers to changes in allele frequencies within a population; macroevolution involves larger-scale changes that can result in new species.
Genetic Variation: Differences among individuals in the composition of their genes or DNA sequences.
Mutation and New Alleles: Mutations are changes in DNA that create new alleles and are the ultimate source of genetic variation.
Types of Mutations: Point mutations, insertions, deletions, duplications, etc.
Sexual Reproduction: Increases genetic variation by recombining alleles in new ways.
Hardy-Weinberg Principle
Purpose: Provides a mathematical model to study genetic variation in populations under ideal conditions (no evolution).
Equation:
where p and q are the frequencies of two alleles.
What It Measures: The expected genotype frequencies in a non-evolving population.
Mechanisms of Evolution in Detail
Genetic Drift: Random changes in allele frequencies, especially in small populations.
Founder Effect: When a few individuals start a new population, leading to reduced genetic variation. Example: High frequency of certain inherited disorders in isolated human populations.
Bottleneck Effect: A sudden reduction in population size due to a disaster, reducing genetic diversity. Example: Northern elephant seals after hunting reduced their numbers.
Gene Flow: Movement of alleles between populations, which can increase or decrease genetic variation.
Natural Selection and Adaptive Evolution: Differential survival and reproduction lead to adaptation.
Relative Fitness: The contribution an individual makes to the gene pool of the next generation relative to others.
Types of Selection
Directional Selection: Favors individuals at one end of the phenotypic range. Example: Larger beak size in finches during droughts.
Stabilizing Selection: Favors intermediate variants. Example: Human birth weight.
Disruptive Selection: Favors individuals at both extremes of the phenotypic range.
Sexual Selection: Selection for traits that improve mating success.
Environmental Impacts: Changing environments can alter selective pressures and evolutionary outcomes.
Chapter 24 – Origin of Species
Speciation and Reproductive Isolation
This chapter examines how new species arise, the biological species concept, and the mechanisms that prevent gene flow between species.
Speciation: The process by which one species splits into two or more species.
Biological Species Concept: Defines a species as a group of populations whose members can interbreed and produce viable, fertile offspring.
Reproductive Isolation Mechanisms
Prezygotic Barriers: Prevent fertilization from occurring.
Habitat Isolation: Populations live in different habitats. Example: Two species of garter snakes, one terrestrial and one aquatic.
Temporal Isolation: Species breed at different times. Example: Eastern and Western spotted skunks breed in different seasons.
Behavioral Isolation: Unique courtship rituals. Example: Different bird songs.
Mechanical Isolation: Morphological differences prevent mating. Example: Incompatible insect genitalia.
Gametic Isolation: Sperm and egg are incompatible. Example: Sea urchin species with different binding proteins.
Postzygotic Barriers: Prevent hybrid offspring from developing into viable, fertile adults.
Reduced Hybrid Viability: Hybrids fail to develop or are frail. Example: Salamander hybrids.
Reduced Hybrid Fertility: Hybrids are sterile. Example: Mule (horse × donkey).
Hybrid Breakdown: First-generation hybrids are viable and fertile, but offspring are weak or sterile.
Limitations of Biological Species Concept: Does not apply to asexual organisms or fossils; gene flow can occur between distinct species.
Modes of Speciation
Allopatric Speciation: Populations are geographically separated, leading to divergence.
Sympatric Speciation: Speciation occurs in populations that live in the same geographic area. Example: Cichlid fish in African lakes.
Hybrid Zones and Speciation Over Time
Hybrid Zones: Regions where different species meet and mate, producing hybrids.
Outcomes of Hybrid Zones Over Time:
Reinforcement: Hybrids are less fit, strengthening reproductive barriers.
Fusion: Barriers weaken, and 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 explores the broad patterns of evolution above the species level, the history of life on Earth, and the evidence provided by the fossil record.
Macroevolution: Evolutionary change above the species level, including the origin of new groups and mass extinctions.
Early Earth Conditions: Earth’s early environment was suitable for the origin of life, with water, energy sources, and simple molecules.
Fossils and the Fossil Record
Types of Fossils: Body fossils (bones, shells), trace fossils (footprints, burrows), and chemical fossils (molecular evidence).
What the Fossil Record Shows: Provides evidence of the history of life, showing changes in species over time.
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 that were abundant and widespread.
How Fossils Are Dated: Relative dating (stratigraphy) and absolute dating (radiometric methods).
Geological Time Scale
Eons and Eras: Major divisions of geological time, such as the Precambrian, Paleozoic, Mesozoic, and Cenozoic eras.
Key Events in the History of Life
First Single-Celled Organisms: Prokaryotes, including stromatolites, appeared over 3.5 billion years ago.
Photosynthesis and the Oxygen Revolution: Cyanobacteria produced oxygen, transforming Earth’s atmosphere.
First Eukaryotes and Endosymbiosis: Eukaryotic cells originated through endosymbiosis, where one cell engulfed another.
Origin of Multicellularity: Multicellular organisms evolved, leading to greater complexity.
Cambrian Explosion: Rapid diversification of animal life about 535 million years ago.
Colonization of Land: Plants, arthropods, and tetrapods were among the first to colonize terrestrial environments.
Earth’s Changing Environment
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, eliminated about 96% of marine species.
Cretaceous Mass Extinction: Ended the age of dinosaurs, likely caused by an asteroid impact.
Sixth Mass Extinction: Ongoing, driven by human activities.
Adaptive Radiation: Rapid evolution of diversely adapted species from a common ancestor, often following mass extinctions or the colonization of new environments.
