Introduction to Evolution, Natural Selection, and the Scientific Foundations of Biology

Course Overview: Organismal and Environmental Biology

Course Structure and Expectations

This course introduces students to the foundational principles of organismal biology and evolution, emphasizing the diversity of life, evolutionary mechanisms, and the scientific method. Students will engage in hands-on laboratory work, critical thinking, and scientific communication.

• Required Texts: Biological Sciences (Freeman et al.), Photographic Atlas of Biology (Van de Graff and Crawley), online readings, and laboratory PDFs.

• Assessment: Participation, laboratory assignments, quizzes, three unit exams, and a comprehensive final exam.

• Laboratory Policy: Missing three labs results in automatic course failure.

• Academic Conduct: Strict adherence to university policies on honesty and integrity.

• Disability Services: Accommodations available through Disability Resource Services.

Characteristics of Living Organisms

Defining Life

Biologists use several criteria to distinguish living organisms from non-living entities. These characteristics are foundational to understanding biology.

• Cellular Organization: All living things consist of one or more cells.

• Genetic Information: Cells contain genetic material (DNA/RNA) that is replicated and passed on to offspring.

• Origin of Cells: All cells arise from pre-existing cells.

• Energy Extraction: Cells extract energy from the environment to perform biological work.

• Regulation: Cells regulate their internal environment to maintain homeostasis.

• Biochemical Unity: All cells share essential biochemical mechanisms due to common ancestry.

Example: Escherichia coli bacteria, fallen leaves, dogs, mushrooms, and viruses are all considered when discussing what is alive.

The Cell Theory

Historical Development

The cell theory is a central concept in biology, stating that all living organisms are composed of cells and that all cells come from pre-existing cells.

• Microscope Invention: 1590s by the Janssens.

• Robert Hooke: Described cells in plant tissue (1650s).

• Anton von Leeuwenhoek: Observed unicellular organisms.

Evolution: The Unifying Theory of Biology

Foundations and Historical Perspectives

Evolution explains the diversity of life and is the central unifying theory in biology. The characteristics of living things are best understood in light of their evolutionary history.

• Th. Dobzhansky: "Nothing in biology makes sense except in the light of evolution."

• Tree of Life: Represents the complete, 4-billion-year history of life, showing relationships among all living organisms.

Philosophical Models of Diversity

Philosophers and scientists have proposed various models to explain the diversity of life:

Model	Main Idea
Plato	Typological thinking; species are unchanging, perfect types.
Aristotle	Great chain of being; species are fixed types arranged in a hierarchy.
Lamarck	Species change over time; acquired traits are inherited.
Darwin & Wallace	Species change through time via common ancestry and natural selection.

Evolution by Natural Selection

Darwin and Wallace's Contributions

Darwin and Wallace proposed that all living organisms are descended from a common ancestor and that evolution occurs by natural selection.

• Variation: Individuals in a population vary in traits.

• Inheritance: Offspring inherit traits from parents.

• Competition: Organisms compete for limited resources.

• Differential Survival: Traits that increase survival and reproduction become more common.

Equation: Change in gene frequency over time can be described by the Hardy-Weinberg equation: $p^2 + 2pq + q^2 = 1$

Artificial vs. Natural Selection

• Artificial Selection: Humans select for desired traits (e.g., dog breeds, pigeon breeds).

• Natural Selection: Traits that confer survival advantage are selected in nature.

Adaptation

Adaptations are traits that improve an organism's ability to survive and reproduce in its environment.

• Examples: Beak shapes in Galapagos finches, web types in spiders.

Domestication and Experimental Evidence

Silver Fox Experiment

The domestication of animals provides a model for understanding how selection can rapidly change populations.

• Dr. Belyaev's Hypothesis: Domestication results from changes in gene frequencies influencing behavior.

• Experiment: Foxes bred for low or high fear responses; measured behavioral and genetic changes over generations.

• Findings: Domestication can occur rapidly under strong selection; gene frequencies and behaviors changed within a few generations.

Additional info: Modern genetic studies (e.g., by Dr. Anna Kukeova) map genes associated with domestication traits in foxes.

The Scientific Method in Biology

Formulating and Testing Hypotheses

Science relies on the formulation of testable hypotheses and the collection of data to support or refute them.

• Testable Hypotheses: Must be falsifiable and supported by data.

• Scientific Process: Hypotheses are continually tested and refined as new data emerge.

Summary of Key Concepts

• Evolution is the central principle of biology, explaining the diversity and adaptation of life.

• All living organisms consist of cells and share a common ancestry.

• Natural selection drives evolutionary change by favoring traits that enhance survival and reproduction.

• Scientific knowledge advances through testable hypotheses and evidence-based reasoning.