Rucete ✏ Campbell Biology In a Nutshell
Unit 4 MECHANISMS OF EVOLUTION — Concept 22.1 The Darwinian Revolution Challenged Traditional Views of a Young Earth Inhabited by Unchanging Species
The Darwinian revolution fundamentally changed how scientists viewed life on Earth, introducing the concept of evolution through "descent with modification." Darwin's ideas emerged from observing nature, influences from other scientists, and his worldwide travels, leading to a profound scientific revolution in biology.
Darwin's Observations and the Unity of Life
Darwin noted three key observations about life:
Organisms are well-adapted to their environments.
Life shows remarkable unity (shared characteristics).
Life is incredibly diverse.
He concluded these observations can be explained by evolution, defined as:
Descent with modification: Species accumulate differences from ancestors as they adapt.
Also defined as genetic changes in populations over generations.
Evolution: Pattern and Process
Evolution can be viewed in two ways:
Pattern: Evidenced by observable data from biology, geology, and chemistry, showing life has evolved over time.
Process: Mechanisms causing evolutionary change, explaining how life evolves.
Early Ideas About Life's Organization
Greek philosopher Aristotle viewed species as fixed and organized life forms into a linear hierarchy known as the scala naturae ("scale of nature").
The Old Testament suggested species were individually created and perfect, influencing early Western views.
Classification and Linnaeus
Carolus Linnaeus developed a hierarchical classification system grouping similar species (genus, family, etc.).
Linnaeus believed these groupings reflected patterns of divine creation rather than evolutionary relationships.
Later, Darwin argued that classification should reflect evolutionary relationships.
Fossils and Geologic Change
Study of fossils (paleontology) greatly influenced evolutionary thought.
Georges Cuvier observed that older fossils differed more from modern organisms and inferred extinctions but rejected evolution, believing sudden catastrophic events caused extinctions.
Geologists James Hutton and Charles Lyell proposed gradual geological processes shaping Earth, suggesting Earth was much older than traditionally believed, significantly influencing Darwin.
Lamarck’s Hypothesis of Evolution
Jean-Baptiste de Lamarck proposed the first mechanism of evolution based on two principles:
Use and disuse: Body parts used extensively become stronger; unused parts deteriorate.
Inheritance of acquired characteristics: Organisms pass modifications to offspring (incorrect mechanism).
Modern genetics disproves Lamarck's mechanisms, but his recognition of gradual evolutionary change remains important.
In a Nutshell
Darwin’s theory challenged the traditional views of fixed species and a young Earth. He proposed evolution as "descent with modification," backed by scientific observations, fossil records, and influences from earlier thinkers. Though Lamarck’s specific mechanisms were incorrect, his idea of gradual evolutionary change was significant in setting the stage for Darwin’s revolution.