What Is Theoretical about the Darwinian View of Life? • In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena
Darwin Introduces a Revolutionary Theory
• A new era of biology began on November 24, 1859, the day Charles Darwin published On the Origin of Species by Means of Natural Selection
• The Origin of Species focused biologists’ attention on the great diversity of organisms
• Darwin made two major points in his book:
• Many current species are descendants of ancestral species
• Natural selection is a mechanism for this evolutionary process
Resistance to the Idea of Evolution
• The Origin of Species
– Shook the deepest roots of Western culture
– Challenged a worldview that had been prevalent for centuries
• The Greek philosopher Aristotle viewed species as fixed and unchanging
• The Old Testament holds that species were individually designed by God and therefore perfect
• Carolus Linnaeus interpreted organismal adaptations as evidence that the Creator had designed each species for a specific purpose
• Linnaeus was a founder of taxonomy, the branch of biology concerned with classifying organisms
Fossils, Cuvier, and Catastrophism
• The study of fossils helped to lay the groundwork for Darwin’s ideas
• Fossils are remains or traces of organisms from the past, usually found in sedimentary rock, which appears in layers or strata
• Paleontology, the study of fossils, was largely developed by French scientist Georges Cuvier
• Cuvier advocated catastrophism, speculating that each boundary between strata represents a catastrophe
Theories of Gradualism
• Gradualism is the idea that profound change can take place through the cumulative effect of slow but continuous processes
• Geologists Hutton and Lyell perceived that changes in Earth’s surface can result from slow continuous actions still operating today
• This view strongly influenced Darwin’s thinking
Lamarck’s Theory of Evolution
• Lamarck hypothesized that species evolve through use and disuse and the inheritance of acquired traits
• The mechanisms he proposed are unsupported by evidence
The Voyage of the Beagle
• During his travels on the Beagle, Darwin collected specimens of South American plants and animals
• He observed adaptations of plants and animals that inhabited many diverse environments
• His interest in geographic distribution of species was kindled by a stop at the Galápagos Islands near the equator west of South America
Darwin’s Focus on Adaptation
• In reassessing his observations, Darwin perceived adaptation to the environment and the origin of new species as closely related processes
• From studies made years after Darwin’s voyage, biologists have concluded that this is indeed what happened to the Galápagos finches
Descent with Modification
• The phrase descent with modification summarized Darwin’s perception of the unity of life
• The phrase refers to the view that all organisms are related through descent from an ancestor that lived in the remote past
• In the Darwinian view, the history of life is like a tree with branches representing life’s diversity
Survival of the Fittest
• Individuals with characteristics that are not well suited for their environment either die or leave few offspring.
• Darwin called this natural selection
Artificial Selection
• In artificial selection, humans have modified other species over many generations by selecting and breeding individuals with desired traits
Summary of Natural Selection
• Natural selection is differential success in reproduction from interaction between individuals that vary in heritable traits and their environment
• Natural selection produces an increase over time in adaptation of organisms to their environment
• If an environment changes over time, natural selection may result in adaptation to these new conditions
What Is Theoretical about the Darwinian View of Life?
• In science, a theory accounts for many observations and data and attempts to explain and integrate a great variety of phenomena
• Darwin’s theory of evolution by natural selection integrates diverse areas of biological study and stimulates many new research questions
