Darwin's Big Idea and How it Changed Biology

Lecture 2

The Argument From Design

• Proposed by William Paley

• The complexity, order, and purpose observed in the natural world are evidence of an intelligent creator or designer

• Watchmaker Analogy

The Inheritance of Acquired Characteristics

• Jean-Baptiste de Lamarck

• The traits organisms acquire through their lifetime, such as those gained by use or disuse, can be passed directly to its offspring

• The Giraffe’s Neck

Germplasm Theory

• August Weismann

• Inheritance only by germ cells (gametes); somatic cells (soma/body) do not function as agents of heredity

• Thus genetic information cannot be passed from soma to gametes and onto next generation

Theory of Evolution

• Charles Darwin and Alfred Russel Wallace

• All organisms have descended with modification from a common ancestor (thus, living things change over time)

• The process leading to evolution is natural selection operating on variation among individuals 

Variation

Individual variation in a population

Heredity

Progeny resemble their parents more than unrelated individuals

Differential fitness

Some forms are more successful at (surviving and) reproducing then others in a given environment

Important Elements of Darwin’s Theory

• Evolution occurs primarily at the level of populations (individuals don’t evolve)

• Variation is not directed by environment (individuals don’t induce adaptive variation when needed)

• Most fit type depends on the environment

• ‘Survival of the fitter’: Evolution works with available variation, and will not necessarily achieve perfection

Implications of Darwin’s Theory of Evolution

• Concepts of a changing universe

  • Replaced views of a static world

• A phenomenon with no purpose

  • Natural selection revealed how complex adaptations with important ‘functions’ can arise through an unplanned process