Descent with Modification22: A Darwinian View of Life
Chapter 22: Descent with Modification: A Darwinian View of Life
Key Concepts
Darwinian Revolution: Challenged traditional views of a young Earth inhabited by unchanging species.
Descent with Modification by Natural Selection: Explained the adaptations of organisms and the unity and diversity of life.
Evolution Evidence: Supported by an overwhelming amount of scientific evidence.
Concept 22.1: The Darwinian Revolution Challenged Traditional Views
Evolution Definition
Darwin’s phrase: "Descent with modification".
Scala Naturae and Classification of Species
Aristotle's View: Species are fixed and arranged in a scala naturae ("scale of nature").
Old Testament Belief: Species individually designed by God and thereby perfect.
Classification of Life’s Diversity
Carolus Linnaeus:
Interpreted organismal adaptations as evidence of divine design.
Adopted a nested classification system, grouping similar species into increasingly general categories.
Developed the binomial naming system (e.g., Homo sapiens).
Ideas About Change Over Time (1 of 3)
Fossils: Remains or traces of past organisms found in layers of sedimentary rock.
Ideas About Change Over Time (2 of 3)
Georges Cuvier: Developed paleontology, speculated that boundaries between strata represented catastrophic events.
Ideas About Change Over Time (3 of 3)
James Hutton and Charles Lyell:
Proposed that Earth's surface changes occur from slow, continuous actions.
Influenced Darwin's thinking significantly.
Lamarck’s Hypothesis of Evolution
Lamarck's Idea: Species evolve through the use and disuse of body parts, with inheritance of acquired characteristics.
Critique: Lamarck's mechanisms are unsupported by evidence.
Descent with Modification: A Darwinian View of Life
Inquiry Session: Discuss the inheritance of acquired characteristics contradictory to Darwin’s view.
Concept 22.2: Descent with Modification by Natural Selection Explains the Adaptations of Organisms
Pre-Darwin Views
The early 19th century belief was that species remained unchanged since their creation.
Darwin’s Research
Charles Darwin:
Had a consuming interest in nature.
Studied unsuccessfully in medicine, then theology at Cambridge University.
Served as a naturalist during Captain Robert FitzRoy's 5-year voyage on the Beagle.
The Voyage of the Beagle
Collected specimens of South American flora and fauna.
Observed:
Fossils similar to living species from the same region.
Living species resembling other species from nearby areas.
Earthquake effects on land uplift in Chile.
Noted geographic distribution of species, especially in the Galápagos Islands.
Darwin’s Focus on Adaptation
Adaptations: Inherited traits that enhance survival and reproduction in specific environments.
Closely linked to the origin of new species, as seen in the Galápagos finches.
The Origin of Species (1 of 2)
In 1844, Darwin wrote an essay on natural selection, not released publicly.
Natural Selection: Process where individuals with favorable inherited traits survive and reproduce more successfully.
In 1858, received a manuscript from Alfred Russell Wallace on a similar theory, prompting Darwin to publish The Origin of Species.
The Origin of Species (2 of 2)
Presented three broad observations:
The unity of life.
The diversity of life.
The match between organisms and their environment.
Descent with Modification (1 of 3)
First edition of The Origin of Species did not use the term evolution.
"Descent with modification" summarizes the unity of life, indicating relatedness through a common ancestor.
Descent with Modification (2 of 3)
Darwin’s view likens the history of life to a tree:
Branching pattern explains life’s diversity and large anatomical gaps due to extinction events.
Artificial Selection and Natural Selection
Artificial Selection: Humans selectively breed individuals for desired traits.
Observations Leading to Inferences:
Population members often show trait variation.
Species can produce more offspring than the environment can support, implying competition.
Individuals with advantageous traits pass those traits onto offspring, influencing future generations.
Key Features of Natural Selection
Individuals with heritable traits have higher survival and reproduction rates.
Natural selection increases adaptability over time.
Populations evolve, not individuals.
Concept 22.3: Evolution is Supported by Scientific Evidence
Four types of data indicating evolution:
Direct Observations
Homology: Similarity due to common ancestry.
Fossil Record
Biogeography: Geographic distribution evidence.
Direct Observations of Evolutionary Change
Natural Selection Cases:
Soapberry bugs adapting beak size to different fruits.
Evolution of drug-resistant bacteria.
Evolution of Drug-Resistant Bacteria (1 of 3)
Staphylococcus aureus: A common bacterium; strain MRSA is resistant to antibiotics.
Developed resistance shortly after penicillin and methicillin introduction.
Evolution of Drug-Resistant Bacteria (2 of 3)
Mechanism: Methicillin inhibits a protein used in bacterial cell walls. MRSA uses a different protein that’s unaffected.
Homology
Definition: Similarity resulting from a common ancestor; encompasses anatomical and molecular homologies.
Homologous Structures: Reflect variations adapted from a common ancestor.
Vestigial Structures: Remnants of features that were functional in ancestors.
Fossil Record
Provides evidence about species' extinction, origin of new groups, and evolution over time.
Biogeography
Study of species distribution with evidence leading to the understanding of species evolution influenced by continental drift.
Conclusion
Theoretical Aspect of Darwin’s View: A theory unifying many observations explaining and integrating diverse biological phenomena. Ongoing research continues to enhance understanding.