Chapter 18 Evolution and the Origin of Species
Chapter 18 Evolution and the Origin of Species
Be Able To:
Summarize the observations, reasoning, and historical context that led to Darwin’s theory of evolution by natural selection.
List and explain the main points of Darwin’s Theory.
Describe what is not included in Darwin’s Theory.
Describe and explain the scientific evidence that supports the theory of evolution by natural selection.
Explain why "Darwin’s Theory" is a scientific theory.
Explain the different ways to define species.
Explain the different ways biological species remain genetically separate from each other.
Describe the processes hypothesized to explain how new species may arise.
Explain and interpret examples of evidence supporting these hypotheses.
Chapter 18 - Topics
What is EVOLUTION?
Views of Life Before Darwin
Charles Darwin & His Theory
What’s NOT in Darwin’s Theory (Misconceptions)
Evidence of evolution
Direct observation
Fossil record
Homologous structures & Vestigial structures
Convergence
Biogeography
Molecular biology
Formation of new species
Ways to Define Species
Biological Species Concept
Speciation & Evolution
Allopatric Speciation & Sympatric Speciation
Reconnection
Speciation Rates
What is Evolution?
Definition of Evolution:
Evolution refers to the change in organisms throughout Earth's history.
Current life forms are different from and descended from earlier life forms.
Descent with modification:
Proposed by Charles Darwin.
Involves gradual genetic changes driven by natural selection, which leads to the diversity of life observed today.
Key processes include:
Change in the genetic makeup of an organism leads to new traits.
Traits that provide advantages in a particular environment become prevalent.
Descendants of organisms inherit these advantageous traits and continue to diversify over generations.
Views of Life Before Darwin
Ancient Philosophy:
The understanding of life was significantly influenced by Ancient Greek and Roman philosophies, as well as spiritual and philosophical traditions from non-Western cultures such as Hinduism and Buddhism.
Age of Reason (1700s-1800s):
Emergence of scientific inquiry emphasized from observation and experimentation.
Early scientists started challenging established doctrines, transforming the view of nature.
Key Philosophers/Scientists Before Darwin:
Georges-Louis Leclerc Comte de Buffon (1707-1788): Considered variation among species.
Carl Linnaeus (1707-1778): Developed the binomial system for naming organisms (e.g., Homo sapiens).
James Hutton (1726-1797): Proposed the concept of gradualism, suggesting geological features were shaped by slow processes over time.
Charles Lyell (1797-1875): Advocated uniformitarianism, asserting that the same geological processes observed in the present were responsible for past changes.
Jean-Baptiste Lamarck (1744-1829): Suggested that organisms evolve through the use and disuse of traits and that acquired characteristics are inherited.
Darwin’s Theory
Two Main Ideas:
Descent with modification:
All life is related through common ancestry and has evolved over time.
Natural Selection:
Natural selection is the mechanism behind evolution, where individuals with traits better suited to their environments are more likely to survive and reproduce.
Historical Context of Darwin’s Development of Theory:
During the H.M.S. Beagle voyage (1831-1836), Darwin collected specimens, observed geographic variation of species, and noted how adaptations corresponded to environmental factors.
He observed distinct finch beak shapes in the Galapagos Islands and hypothesized they adapted from a common ancestor to exploit different food sources.
Evidence of Evolution
Direct Observation
Example: Soapberry bugs adapting their beak shape to different food sources (e.g., balloon vine versus non-native raintree fruit).
Observations showed that beak lengths evolved quickly in response to ecological changes, reflecting natural selection in action.
Fossil Record
Fossils provide evidence of extinct species and common ancestors. Examples include:
Transition forms such as whales which show changes in limb structures over millions of years, demonstrating evolutionary change (e.g., from land-dwelling ancestors to aquatic forms).
Homologous Structures
Structures that are similar due to shared ancestry but serve different functions.
Example: Similar limb bone structures in humans, whales, and bats indicate a common evolutionary origin despite functional adaptations.
Vestigial Structures
Vestigial structures are remnants of ancestral features that no longer serve a function.
Example: Eyes of blind cave salamanders suggest descent from ancestors that had functional eyesight.
Convergence
Convergence leads to analogous structures where unrelated species develop similar adaptations in response to similar environmental challenges.
Example: The torpedo shape of dolphins and sharks suggests adaptations for efficient swimming in aquatic environments.
Biogeography
Distribution of species around the world correlates with historical movements of land masses (e.g., Pangea).
Example: Distinct species found on islands that are closely related to species on the nearest mainland.
Molecular Biology
DNA Analysis: Shows genetic similarities among closely related species, reinforcing common ancestry.
Universality of the Genetic Code: Indicates that all living organisms share a common molecular foundation.
Formation of New Species
Ways to Define Species
Morphological Species Concept: Based on physical traits and appearances.
Ecological Species Concept: Defined by its ecological niche.
Phylogenetic Species Concept: Based on evolutionary ancestry and genetic data.
Biological Species Concept: Centers on reproductive isolation and the ability to produce viable offspring.
Species Reproductive Isolation
Prezygotic Barriers: Prevent mating or fertilization. Examples include:
Temporal isolation
Habitat isolation
Behavioral isolation
Postzygotic Barriers: Occur after fertilization. Examples include:
Reduced hybrid viability
Reduced hybrid fertility
Hybrid breakdown
Speciation Processes
Allopatric Speciation: Occurs due to geographical isolation, wherein species evolve separately (e.g., mountain ranges separating populations).
Sympatric Speciation: Takes place in the same geographic area; often due to behavioral, habitat, or genetic factors influencing reproduction.
Example: Apple maggot fly diverging based on fruit resources.
Reconnection and Speciation Rates
Hybrid Zones: Areas where related species interact and potentially interbreed.
Speciation Rates:
Gradual Speciation: Slow divergence through continuous small changes.
Punctuated Equilibrium: Rapid changes followed by long periods of stability in a species.
Misconceptions of Evolution
Common misconceptions include:
Evolution is just a theory, individuals evolve, and evolution explains the origin of life.
Organisms evolve on purpose, and species evolve into 'higher' beings.
Many believe that evolution results solely from random mutations and creates new forms through dramatic changes.
Just a Theory?
Evolution is classified as a scientific theory, defined as a well-supported explanation with predictive capability.
Example: Theory of gravity and its implications in understanding evolution.
What’s Not Explained by Darwin’s Theory
Origin of life.
Mechanisms for generating variation (how traits arise).
Mechanisms of inheritance.
Existence of sudden changes in the fossil record.
Emergence of entirely new traits or species.
Conclusion
Darwin's foundational theory of evolution through natural selection explains the diversity and complexity of life, providing insight into biological processes and species interactions. Current advancements in genetics and molecular biology continue to support and elaborate on foundational evolutionary theories.