Unit 3: Introduction to Evolution

Definition of Evolution

• Evolution: Cumulative change in the heritable characteristics of a population over time.
• Key terms:
  • Cumulative: All increasing changes occurring.
  • Heritable/Inheritable: Changes must be passed on genetically across generations.
  • Population: Changes affect the entire population, not just individuals.
  • Time: Refers to gradual development over many generations.
• Result: Biodiversity within populations.

Evolutionary Thought

• Early biological thought: Did not include evolution.
• 18th Century: Church's influence led to belief in creationism (fixed and unchanging life forms).
• Emerging Evidence: Discovery of species diversity and similarities led to considerations of species change and common ancestry.

Common Ancestry

• Definition: An organism that is the shared ancestor of two or more descendant groups.
• Modern biology posits all life descended from a common ancestor or ancestral gene pool.

Theories of Evolution

• Jean Baptiste de Lamarck: Proposed first evolutionary theory.

  • Believed organisms change due to a universal force, use/disuse of body parts, and acquired characteristics.
  • Although incorrect, highlighted adaptation and influenced Darwin.

• Charles Lyell: Geologist, influenced Darwin with ideas about Earth's changes and competition.

• Thomas Malthus: Economist, proposed population growth outpaces resources, affecting all living things.

Charles Darwin and Natural Selection

• Research Basis: Observations in South America, Galapagos Islands, domestic breeding, other scientific work.
• Theory of Natural Selection:
  • Published in "Origin of Species" (1859).
  • Natural selection leads to species best suited to environment reproducing more successfully.
  • Concepts of fitness and adaptation are central.

Natural Selection

• Definition: Nature selects traits that increase population fitness based on environmental demands.
• Examples: Walking Stick insect, antibiotic-resistant bacteria.

Key Points of Evolution by Natural Selection

1. Interaction with environment affects populations, not individuals.
2. Amplifies heritable traits, not acquired traits.
3. Not goal-directed - environment-specific adaptations.

Main Ideas of Darwin’s Theory

1. Overpopulation: Species produce more offspring than environment supports.
2. Competition: Struggle for existence.
3. Variation: Differences among organisms.
4. Survival of the Fittest: Natural selection.
5. Adaptation: Organisms adapt to their environments.
6. Speciation: New species arise from favorable adaptations.

Types of Adaptations

1. Structural: Physical changes (e.g., mimicry, camouflage).
2. Physiological: Metabolic process changes (e.g., venom, enzyme production).
3. Behavioral: Inherited behaviors (e.g., migration, hibernation).

Observing Natural Selection

• Case Studies:
  • Galapagos Finches: Beak size variation due to seed availability.
  • Peppered Moths: Color variation due to industrial changes.
  • Antibiotic Resistance: Bacteria evolving resistance to antibiotics.

Types of Natural Selection

1. Stabilizing Selection: Favors average traits.
2. Directional Selection: Favors one extreme trait.
3. Disruptive Selection: Favors extreme traits over average.

Evidence of Evolution

1. Fossil Record: Shows life changes over time.
2. Biogeography: Distribution of organisms supports evolution.
3. Homologous Structures: Similar anatomical features due to common ancestry.
4. Embryonic Development: Common embryological stages suggest relatedness.
5. Biochemistry: Similar DNA and proteins indicate common ancestry.

Misconceptions About Humans

1. Humans did not evolve from chimpanzees; share a common ancestor.
2. Humans are not "more evolved" than other lineages.

Selective Breeding of Domesticated Animals

• Domesticated breeds developed via selection and interbreeding with wild species.
• Evidence for rapid evolution.

Population Genetics and Evolution

• Genetics and evolutionary theory are interconnected.
• Population Genetics: Studies gene behavior in populations.
• Gene Pool: Combined genetic material in a population.
• Allele Frequency: How often an allele appears in a population.

Hardy-Weinberg Principle

• Definition: Conditions under which allele frequencies remain stable, indicating genetic equilibrium.
• Five Conditions: Large population, no mutations, random mating, no gene flow, no natural selection.

Mechanisms of Evolution

1. Mutations: Genetic changes introducing new alleles.
2. Genetic Drift: Changes due to chance.
3. Gene Flow: Movement of genes between populations.
4. Nonrandom Mating: Influences gene frequencies.
5. Natural Selection: Adapts populations to environments.

Speciation

• Definition: Origin of new species through isolation and genetic divergence.
• Geographical Isolation: Allopatric speciation due to physical barriers.
• Reproductive Isolation: Sympatric speciation within same area.

Patterns of Evolution

• Divergent Evolution: Isolated group evolves separately.
• Adaptive Radiation: Rapid evolution into diverse species.
• Convergent Evolution: Unrelated species evolve similar traits.
• Co-evolution: Species evolve in response to each other.
• Extinction: End of a species.

Rate of Evolution

• Gradualism: Slow, steady change.
• Punctuated Equilibrium: Long periods of stability interrupted by rapid change.

Summary

This lecture covered the fundamentals of evolution, key theories and mechanisms, and the observable evidence supporting evolutionary processes. Understanding these concepts is crucial for grasping the diversity and adaptability of life on Earth.