Evolutionary Theory Overview

Evolutionary Theory

• A theory is a broad explanation supported by evidence
• Evolution is descent with modification, meaning change in the genetic makeup of a population over time.
• Evolutionary theory is both a pattern (facts observed in nature) and a process (mechanisms causing change)

The Road to Darwin

• Aristotle (384-322 BCE) proposed Scala Naturae, a hierarchical ladder of life.
• Carolus Linnaeus (1707-1778) developed binomial nomenclature for classifying organisms.

Ideas about change over time

• Fossils are remains or traces of past organisms.
• Strata are layers of rock.
• Paleontology is the study of fossils.
• Georges Cuvier (1769-1832) proposed catastrophism (periods of rapid change).
• James Hutton (1726-1797) proposed gradualism, that Earth's features change gradually over long periods.
• Charles Lyell (1797-1875) proposed uniformitarianism, that geological processes have been uniform over geological time.

Jean-Baptiste de Lamarck (1744-1829)

• Lamarck proposed gradual evolutionary change, explaining the fossil record.
• Organisms adapt to their environments.
• He proposed two principles: use and disuse (characteristics acquired during an organism's lifetime can be passed down), and inheritance of acquired characteristics.
• Lamarck was incorrect in the mechanism of transmission of acquired characteristics, but correctly identified that organisms adapt to their environments.

Darwin's Theory of Finches on the Galapagos Islands

• Darwin observed finches with diverse beak shapes and sizes.
• Different beaks and behaviors were suited to specific foods available on various islands.
• This is an example of adaptive radiation.

Adaptive Radiation

• A period of evolutionary change where groups of organisms form many new species.
• Adaptions enable them to fill different ecological roles.

After HMS Beagle Voyage

• Darwin wrote an essay on the origin of species and natural selection in 1844.
• It was not published.
• Alfred Russel Wallace also developed similar ideas.
• Darwin and Wallace jointly presented their ideas in 1858.
• Darwin's book "On the Origin of Species" was published in 1859.

On the Origin of Species

• Darwin's book published in 1859.
• Two main points: Descent with Modification and Natural Selection.

Descent with Modification

• Darwin's phrase for evolution.
• Organisms are related through descent from common ancestors who lived in the past.

Artificial Selection

• Humans modify other species through selective breeding of individuals.
• Examples include cabbage, broccoli, and kale.

Natural Selection

• More offspring produced than can survive.
• Those that survive are "suited" to the environment, are successful in reproduction, and pass genes to offspring.
• Favorable adaptations stay; unfavorable adaptations are lost.
• This results in populations, not individuals, evolving over many generations so organisms are better adapted to their environment.
• Depends on genetic variation within populations.

Evidence for Evolution

• Observations of evolution: Examples include beak changes in soapberry bugs.
• Homology: Similarity in characteristics resulting from shared ancestry.
  • Homologous structures: Variations on a structural theme from a common ancestor (e.g., forelimbs of mammals).
  • Vestigial structures: Remnants of features serving a function in an ancestor (e.g., whale pelvis).
  • Molecular homologies: Similarities in DNA and protein molecules between related organisms.
• Convergent evolution: Similar adaptations in unrelated organisms due to similar environments (e.g., sugar glider and flying squirrel).
• Fossil record: Fossilized remains of organisms that lived in the past confirm the order organisms appeared.
• Biogeography: Geographic distribution of species and similarities in fossils found on recently separated landmasses.

Explore the foundational concepts of evolutionary theory, including its definition and historical context leading to Darwin. Discover how ancient ideas about life's hierarchy, fossils, and geological change have shaped our understanding of evolution over time.