Evolution: A Formal Introduction

Cycle 1: Evolution - A Formal Introduction

Introduction to Evolutionary Theory

• This lecture provides a formal introduction to evolutionary theory, building on the previous discussion of natural selection with HIV.

• It also explores the broader meaning of scientific theories in general.

• The title, "Why Evolution Is True," is an homage to Jerry Coyne's book.

• Charles Darwin's initial sketch of a phylogenetic tree (from his notebooks) depicted the revolutionary idea of universal relatedness among all life on Earth.

Public Opinion on Human Evolution

• Class Survey: An overwhelming majority of students (science/biomedical majors) in the class accept that humans are a product of evolution and related to other life forms.

• Global Survey (Angus Reid Poll, ~20 years ago):

  • Surveyed citizens in $34-35$ developed nations on acceptance of human evolution.

  • Highest Acceptance: Iceland (around $85\%$), Scandinavian countries generally high.

  • Lowest Acceptance: Turkey (around $25\%$ accepting, $50\%$ rejecting).

  • Second Lowest Acceptance: United States (around $40\%$ accepting, $40\%$ rejecting, $20\%$ unsure).

    • Rejection in the US often aligns with the belief in Young Earth Creationism (humans created in present form by a supernatural entity, potentially within the last $5000$ years).

• Canadian Survey (National Center for Science Education, recent):

  • Around $64\%$ of Canadians accept human evolution.

  • Around $21\%$ support Young Earth Creationism.

  • Support for evolution varies by age (younger demographics show more support) and political affiliation.

Controversy and Conflict with Belief Systems

• Since Darwin's On the Origin of Species (1859), evolution has been controversial among the general public, unlike gravitational theory or germ theory.

• Scientific Consensus: Among scientists, there is overwhelming support for the evidence of evolution.

• Core Controversy: The main controversial aspect of Darwin's theory, then as now, is the idea that humans were not specially created by a supernatural entity, but are instead one species among millions, with an evolutionary history related to all other life.

• This idea can conflict with some religious traditions, creation stories, and belief systems.

Belief Systems vs. Scientific Theories

• Belief System: A set of principles, moral codes, personal philosophies, or religious traditions accepted on faith.

  • Examples: Universal human rights, the belief that murder is wrong.

  • Key Characteristics: Not intended to be tested scientifically; do not change based on testing or evidence.

• Scientific Theory: A coherent set of testable hypotheses or ideas about the natural world.

  • Examples: Theories about gravity, atomic structure, evolution.

  • Key Characteristics: Must be testable and falsifiable; change with evidence.

Characteristics of Scientific Theories

• Testable: There must be a way to empirically investigate the ideas.

• Falsifiable: If a hypothesis is wrong, there must be some real or hypothetical observation or experimental outcome that would demonstrate its incorrectness.

  • Falsifiable does not mean false.

  • Example of Falsifiable Statement: "A bear will run through the classroom at $10:00$ today." (If it doesn't happen, the statement is falsified).

  • Example of Non-Falsifiable Statement: "Positive thinking can cure cancer; you just have to try hard enough." (Failure can always be attributed to "not trying hard enough," making it untestable).

  • This is crucial for the scientific method: theories are tested, and if falsified, they are rejected or modified.

The Dover Trial and Intelligent Design

• The Dover Trial (Pennsylvania, 2005) occurred when a school board mandated teaching Young Earth Creationism (Intelligent Design) alongside evolution in biology classes.

• The judge ruled that Intelligent Design does not belong in science classes.

• Reason: Intelligent Design is not scientific because it is not falsifiable.

  • It appeals to supernatural beings who can hide evidence, making it impossible to prove wrong through observation or experiment. It lacks testability.

Key Aspects of Evolutionary Theory (Darwin's Theory)

• Darwin called evolution "descent with modification from a common ancestor."

1. Evolution (Change):

   • Populations evolve: allele frequencies and phenotypic frequencies change from one generation to the next.

   • This can occur over hundreds of thousands of years (e.g., changes in human skull shape) or much faster (e.g., peppered moth coloration during the Industrial Revolution, HIV drug resistance within months).

2. Common Ancestry:

   • All life on Earth is related and descended from a single common ancestor (the Last Universal Common Ancestor, LUCA).

   • Humans are closely related to chimpanzees and gorillas, and more distantly to cabbages, oak trees, beetles, and bacteria.

3. Speciation:

   • The process by which one lineage splits into two or more reproductively isolated daughter groups.

   • Explains how life diverged from LUCA into millions of species.

   • Example: Salamanders around California's Central Valley, once a single species, are in the process of speciating, showing varying appearances and reproductive isolation.

4. Evolution as a Variational Process (Not Transformational):

   • Lamarckian (Transformational) View (Rejected): Individuals change their phenotype during their lifetime to better suit the environment, and these acquired traits are passed to offspring (e.g., a short-necked giraffe stretching its neck and passing a longer neck to its offspring).

     • Analogy: In Pokémon, a Munchlax evolving into a Snorlax is development within an individual's lifetime, not biological evolution.

   • Darwinian (Variational) View (Accepted): Evolution acts on existing variation within a population.

     • Individuals do not evolve; populations evolve across generations.

     • Some existing variants within a population are more successful (survive longer, produce more offspring) than others, leading to changes in population-level frequencies of traits over time.

     • Diagram: A population with diverse shapes and colors; if dark and stretched-out forms are advantageous, they will preferentially survive and reproduce, increasing their frequency in the next generation.

5. Gradualism and Transitional Forms:

   • Evolutionary change is gradual and takes many generations.

   • Large evolutionary changes require vast amounts of time (thousands to millions of generations).

   • Transitional Forms (Missing Links): Intermediate fossils that demonstrate evolutionary transitions between different groups.

     • Example: Archaeopteryx shows both bird-like traits (feathers) and dinosaur-like traits (teeth), providing evidence for the transition from theropod dinosaurs to modern birds.

6. Natural Selection and Adaptation:

   • Selection: A major cause of evolution (both natural and sexual selection).

   • Adaptation: When selection causes a population to become better suited to its environment (e.g., HIV becoming AZT-resistant, polar bears developing white fur for camouflage).

   • Selection is the only evolutionary mechanism that causes adaptation.

   • Not the Only Cause of Evolution: Other factors like genetic drift, gene flow, and mutation can also change allele frequencies in a population, but they don't necessarily lead to adaptation (may be neutral or even harmful).

Common Misconceptions About Evolutionary Theory

1. Humans descended from chimpanzees.

   • False: Humans are related to chimpanzees; we share a common ancestor, but neither species descended directly from the other. We are evolutionary cousins.

2. Species can be ranked on a hierarchy ("scale of nature"), with humans at the top as most highly evolved.

   • False: All species currently alive on Earth have evolved from the same Last Universal Common Ancestor (LUCA) over the same amount of evolutionary time.

   • Evolution is a branching bush, not a ladder. While some species (e.g., horseshoe crabs) might exhibit less morphological change over long periods, they have still been evolving for the same duration. Less phenotypic change does not equate to being "less evolved."

3. Mutations are directed towards the needs of the organism.

   • False: Mutations are random errors. Their fate (whether they become more or less common) depends on the selective environment, but their origin is undirected.

4. Selection is a source of perfection; it makes organisms perfectly suited to their environment.

   • False: Adaptation makes organisms better suited, but not perfect, due to several reasons:

     • Environmental Change: Environments often change faster than evolution can keep pace (e.g., climate change affects species adapted to older conditions).

     • Trade-offs: Improving one trait may compromise another (e.g., stronger bones could mean more body mass; very large brains might necessitate wider hips in females, affecting locomotion).

     • Organisms are typically "good enough" rather than perfectly adapted.

5. All evolution is due to selection.

   • False: While selection is the only cause of adaptation, other evolutionary mechanisms like genetic drift, gene flow, and mutation also cause populations to evolve. These processes will be discussed later in the course.

Applying Evolutionary Concepts

• Example: Archaeopteryx: The finding of Archaeopteryx (with both bird and dinosaur features) is most relevant to the idea of gradualism and the existence of transitional forms.

• Example: Dolphin Hind Limbs: The transient development of hind limbs in fetal dolphins, which are later reabsorbed, is highly informative of common ancestry. It suggests descent from an ancestral species that possessed hind limbs.

Reminder: No OWL quiz this weekend.