Darwin and the Galapagos Islands

Galapagos Islands

• One of the most volcanic places on Earth.
• Crossroads of four major ocean currents, leading to high marine diversity.
• Islands formed between 700,000 and 4.2 million years ago (oldest submerged - 8 million years ago, plume - 90 million years ago)
• Geological and ecological differences are tied to the ages of the islands.
• Parallel between species morphology, behavior, geography, and adaptation to the environment.

Influences of Darwin's Work

• Lyell's Geology - Rejected the six-day creation theory.
• Thomas Robert Malthus - Many more organisms are born than can survive due to limited resources. This leads to competition and only the strong survive.

Darwin's Contribution

• Demonstrated the fact of evolution and defined it as descent with modification.
• Offered an explanatory mechanism for evolution - natural selection.
• Survival and mortality are key to natural selection.
• Natural Selection preserves favorable individual differences and variations while destroying less adaptable ones.
• Argued against a purely competitive view of evolution. He believed the success of human and animal evolution was tied to the evolution of compassion.

Alfred Russel Wallace

• Explored the Malay Archipelago from 1848 to 1862.
• In 1857, he wrote "On the Tendency of Variation to Depart Indefinitely from the Original Type," outlining his theory of evolution.

Five Parts of Natural Selection

• Heredity of most features
• Heritable variation in the population.
• Variation leads to differential survival and reproductive success among variations.
• Differential survival and reproduction leads to changes in the frequency of characters within a population (they will diverge).
• If the process continues for long enough, parent and daughter species can no longer interbreed.

Gradual Evolution

• Darwin believed in gradualism: changes happen slowly and gradually.
• This was influenced by the Uniformitarianism school of thought.

Industrial Melanism

• Peppered moth (Biston betularia) exists in two varieties: melanic and non-melanic.
• Non-melanic forms are virtually invisible against pale-colored backgrounds, while melanic forms are invisible against dark backgrounds.
• Different survival rates occur in environments with different colors.
• Before the Industrial Revolution, the lighter form dominated due to a survival advantage.

Race vs. Subspecies

• Subspecies are biological units below the level of a species.
• Race is a social construct based on physical and cultural traits used to draw arbitrary boundaries between people.
• These physical traits are continuous and do not map neatly onto racial categories.

Microevolution vs Macroevolution

Microevolution

• Time: Generations
• Units: Below species level
• Focus: Processes
• Discipline: Population genetics
• Fitness: Births and deaths of individuals
• Evolution: Changes in allele frequencies over time
• Natural Selection: Individual selection

Macroevolution

• Time: Millions of years
• Units: Above species level
• Focus: Products (patterns of organic diversity)
• Discipline: Paleobiology
• Fitness: Births and deaths of species
• Evolution: Changes in patterns of organic diversity through time
• Natural selection: Species selection

Limits of Species Existence

• Environmental factors exert selection pressure, influencing survival (fitness) of organisms and their offspring.
• This restricts where species can live.
• Limiting factors include:
  • Physiological stress (too much or too little moisture, light, temperature, pH, specific nutrients)
  • Competition with other species
  • Predation, including parasites and diseases
  • Luck
• Tolerance limits of a species indicate environmental factors beyond which a species cannot survive or reproduce.

Species Change Through Time

• Because species live within limits, change in species form and numbers occurs as organisms are forced to adapt to changing environments.
• Random change (mutation, drift) and interactions (gene flow) affect variation within a species and its ability to adapt.
• One species can change into a single new species (anagenesis) or into two or more species (cladogenesis).
• Can happen gradually or rapidly.
• Tempo: Phyletic gradualism or punctuated equilibrium.

Speciation

• Speciation is the development of new species.
• One important mechanism of speciation is geographic isolation (allopatric speciation).
• Sympatric speciation occurs when barriers dividing populations are not physical, like habitat, behavioral, or temporal isolation.

Science and Evolution

• Science is the systematic, critical exploration of material nature.
• The theory of evolution is incredibly well supported.

Scientific Method

• Observations/facts
• Hypothesis formulation
• Testability of the hypothesis
• Hypothesis testing and rejection
• Model development (set of repeatedly tested hypotheses)
• Theory (set of models)

Evolution and Biodiversity

• Evolution acted to create biodiversity.
• Time depth can be assessed through indirect evidence.

The History of Evolutionary Thought

• Evolutionary thought is much deeper than the 1700s, with roots in antiquity.
• It originated in non-European spaces, including ancient Greece, Rome, China, and the medieval Islamic world.
• Ancient philosophers like Aristotle formally formalized some of these ideas, which are precursors to evolutionary theory.

European Kingdoms after the Fall of the Western Roman Empire

• Germanic tribes attacked the vulnerable areas of outer Europe, leading to the formation of multiple kingdoms with different languages, histories, and cultures.
• This event resulted in the near-disappearance of Greek scholarship in the West due to a lack of linguistic and intellectual continuity.
• The period following the fall of the Roman Empire (476 BCE to 1000 for the Early Middle Ages, and to 1500 for all Middle Ages) is considered a dark age for Western Europe.
• Aristotle's work disappeared from Western Europe for centuries.
• The Eastern Roman Empire survived the attacks.