Introduction to Evolution

Introduction to Evolution

The Scientists Behind the Theory

Learning Goals

• To understand the pre-Darwinian ideas involving life and its origins.

• To know the basics of the Theory of Evolution.

Two Schools of Thought

Catastrophism

• Definition: The standard understanding of geology before the 1800s.

• Key Concepts:

  • The Earth's features were believed to have developed suddenly due to violent, short-lived events, possibly worldwide in scope.

  • These catastrophic events were thought to be definitive stages in Earth's history.

  • It was assumed that these events no longer occurred, leading to a stable Earth.

• Example:

  • Great Flood as a case of catastrophe.

• Notable Figure:

  • Developed by George Cuvier.

Uniformitarianism

• Definition: A counter to catastrophism, proposed by Charles Lyell and James Hutton in the 1800s.

• Key Concepts:

  • Suggested that the geological processes that formed the Earth in the past continue to occur in the present day.

  • These processes are continuous and uniform, evolving over long timescales.

  • Example: The formation of the Grand Canyon purportedly took millions of years.

The Questions Arise

• Key Questions:

  • If the Earth is changing, could life also change?

  • Before the acceptance of uniformitarianism, it was believed that no species had gone extinct; all species existed continuously from the origin of life.

  • The concept of a perfect creation was prevalent.

Species Extinction

• Historical Contribution: In 1796, George Cuvier demonstrated that species can and do go extinct.

• Method: Utilized fossil records to support his hypothesis.

• Hypothesis: Proposed that species became extinct during catastrophic events, and new species emerged following these events.

Acquired Characteristics

• Proponent: Jean-Baptiste Lamarck.

• Theory: Believed that organisms could adapt to their environments through the inheritance of acquired traits.

• Key Concept: Organisms could alter their bodies during their lifetimes and pass these changes to their offspring, leading to evolution.

The Struggle for Existence

• Source: Thomas Malthus's “An Essay on the Principle of Population”.

• Key Observations:

  • Noted that unchecked populations can grow exponentially, while resource availability increases linearly.

  • This leads to competition for resources and ultimately a struggle for existence.

• Mechanisms of Restraint:

  • Self-restraint: Individuals may choose to breed less.

  • External factors: Competition and environmental constraints limit population growth.

The Rise of the Theory of Evolution

Charles Darwin

• Background: Born in 1809, Darwin showed an early fascination with nature. He identified himself as a naturalist.

• Key Journey: At age 22, he embarked on a 5-year voyage on the H.M.S. Beagle.

  • Activities: Collected specimens from South America, studied geology, and visited islands, including the Galapagos Islands.

Development of the Theory

• Observations: Through his extensive studies, Darwin began to develop the Theory of Evolution via Natural Selection.

• Collaboration:

  • In 1855, Darwin received a letter from Alfred Wallace, a younger mentee, discussing similar theories of evolution to Darwin’s findings.

  • Their collaboration resulted in a joint paper published in 1858 arguing for natural selection.

• Publication: Darwin published “The Origin of Species” in 1859, detailing his findings and observations.

• Impact: The book gained him widespread recognition as the “Father of Evolution,” while Wallace's contributions became less recognized.

The Theory of Evolution

• Foundational Concept: The characteristics of species evolve from one generation to the next.

• Mechanism of Evolution:

  • Natural Selection: Certain characteristics contribute to survival and reproductive success at greater rates than others.

  • These favored characteristics are then passed on to subsequent generations, leading to evolutionary change.