Overview
This lecture covers the historical development of evolutionary theory, including key concepts, early scientific thinkers, and the progression towards Darwin's theory of natural selection.
The Scientific Method & Key Concepts
- A fact is a verifiable truth; a hypothesis explains observed facts; a theory is a set of tested, not rejected, hypotheses.
- The scientific method involves identifying a problem, stating a hypothesis, and testing it with data.
- Evolution is “descent with modification,” meaning species change over generations.
- Natural selection is the mechanism driving evolutionary change, favoring traits that increase reproductive success.
Early Scientific Thinkers
- Aristotle introduced the “Great Chain of Being,” a hierarchy of organisms without implying biological relationships.
- The idea of “fixity of the species” claimed species never change, aligning with religious beliefs of the unchanging Earth.
- Copernicus proposed a heliocentric universe, challenging Earth-centered views.
- Galileo used observation and the scientific method to support heliocentrism, facing opposition from the Church.
- Newton’s laws of motion and gravity laid groundwork for scientific reasoning.
Early Naturalists and Classification
- John Ray defined species by reproductive compatibility and introduced the genus concept, but still believed in fixity.
- Carol Linnaeus standardized classification with binomial nomenclature (genus + species) and added hierarchical categories.
- Linnaeus controversially classified humans within the animal kingdom.
- Comte de Buffon recognized environmental influence on species and change through adaptation but denied species formation.
Theories Before Darwin
- Erasmus Darwin believed all life descended from a common ancestor and emphasized time, competition, and environment.
- Jean-Baptiste Lamarck proposed the “inheritance of acquired characteristics,” suggesting traits gained during life could be inherited (now disproven).
- Thomas Malthus argued population growth outpaces resources, inspiring the concept of competition in evolution.
- Charles Lyell’s uniformitarianism suggested Earth’s features change very slowly, providing a vast time scale for evolution.
Darwin, Wallace, and Natural Selection
- Charles Darwin’s voyage on HMS Beagle led him to observe variation in finches, inspiring the idea of adaptation via natural selection.
- Alfred Wallace independently formulated the theory of natural selection around the same time as Darwin.
- Natural selection relies on variation, competition, favorable traits, environmental influence, and results in new species over time.
- The unit of natural selection is the individual, but evolution occurs at the population level.
Key Terms & Definitions
- Evolution — Descent with modification across generations.
- Natural Selection — Differential survival and reproduction based on inheritable traits.
- Fixity of the Species — The belief that species are unchanging.
- Binomial Nomenclature — System of naming species with two parts: genus and species.
- Uniformitarianism — Geological processes have operated the same way throughout Earth’s history.
Action Items / Next Steps
- Review early naturalists and their influence on evolutionary theory.
- Prepare for next lecture on Gregor Mendel and the genetics of inheritance.