Darwin's Theory of Evolution Notes

Darwin's Theory of Evolution

Introduction

  • Darwin is known for his concept of evolution.
  • He was from England.
  • His voyage on the H.M.S. Beagle changed how we explain the unity and diversity of life.
What is Evolution?
  • Evolution is the process by which different living organisms are thought to have developed and diversified from earlier forms during Earth's history.
  • It involves change over time.

The Gist of Darwin’s Ideology

  • Evolution explains both the unity and diversity of life through common ancestry and natural selection.
Unity
  • Unity arises from the shared genetic code and fundamental biological processes across all living organisms, stemming from a common ancestor.
Shared Ancestry and Basic Processes
  • Common Ancestry: All life on Earth is believed to have descended from a single common ancestor, the Last Universal Common Ancestor (LUCA).
  • Shared Genetic Code: The genetic code is remarkably similar across all organisms.
  • Basic Biological Processes: Many fundamental biological processes are shared across all life forms.
  • Structural Similarities: Similarities in skeletal structures and organ systems point to a common evolutionary origin.
Diversity
  • Diversity arises from the process of natural selection, where advantageous traits in response to specific environments lead to the formation of new species over time.
Adaptation and Natural Selection
  • Adaptation: Populations adapt to different environments, evolving different traits to better suit their surroundings.
  • Natural Selection: Natural selection favors individuals with advantageous traits, leading to the increase of those traits in a population over time.
  • Organisms with the most fit traits survive and reproduce.
  • Speciation: Over long periods, populations can diverge and become so different that they can no longer interbreed, resulting in the formation of new species.
  • Examples: The wings of birds, bats, and insects evolved independently (convergent evolution) due to similar selection pressures for flight.
Additional Points
  • Evolution involves a comparison of ancient organisms to more modern organisms.
  • It is a study of both physical and genetic traits.
  • The study of the evolutionary history of an organism based on its genes is called phylogeny.
  • The study of phylogeny is completed using clades, and the use of clades is called cladistic analysis.

Darwin’s Observations and the Origin of Species

  • Darwin traveled around the world and collected organisms to observe them.
  • He questioned why organisms look alike but have so much diversity.
  • Darwin published a controversial book called The Origin of Species in 1859.
What Did Darwin Observe?
  • Individual organisms differ phenotypically, and some of this variation is inheritable.
  • Among the tortoises, the shape of the shell corresponds to different habitats.

Key Principles of Darwin's Theory

  • Organisms produce more offspring than can survive, and many that do survive cannot reproduce.
  • Organisms compete for limited resources due to high birth rates.
  • Members of each species compete regularly to obtain food, living space, mates, and the necessities of life.
  • Only those species with a competitive advantage can avoid early deaths and thus survive and reproduce.
The Struggle for Existence
  • The struggle for existence is central to Darwin’s Theory of Evolution.
  • A key factor in the struggle of life to exist is how well the organism’s adaptation suits its ability to compete.
Fitness
  • The competitive ability of an organism to survive and reproduce within its environment is called fitness.
  • Fitness is a measure of adaptations or the result of adaptation.
  • High fitness = High survival of the fittest
  • Low fitness = Low survival of the fittest
Adaptations
  • Adaptations are any inheritable traits that enable the organism to become better suited to compete within its ecosystem.
  • Organisms well-suited (fit) to their environment reproduce at much more successful rates. This is called survival of the fittest by natural selection.

Specific Types of Adaptations

Anatomical Adaptations
  • Structural body parts that give an added advantage.
  • Example: Porcupine’s quills
Protective Adaptations
  • Gives added advantages by hiding the organism to avoid being destroyed or avoiding being food.
    • Mimicry: Superficial resemblance of two or more organisms.
      • A defenseless organism bears close resemblance to a noxious one to avoid being a target.
      • Example: Monarch and Viceroy butterfly.
    • Camouflage: The organism can blend in with its environment to avoid being predation.
Physiological Adaptations
  • Internal functions that allow the organism to survive.
  • Example: Plants that undergo photosynthesis.
Behavioral Adaptations
  • Complex adaptations in which organisms work together to avoid predation.
  • Examples:
    • Hunting in groups
    • Groups of birds flying together

Artificial Selection

  • When nature provides the prized and desired phenotype (physical trait), and man selects it for breeding the next generation.
  • Example: Belgian Blue Cow – selectively bred for bigger muscles.

Survival of the Fittest by Natural Selection

  • When nature selects for an individual to have high fitness, this organism can survive and reproduce.
  • Over many successive generations, only certain individuals reproduce, contributing to an organism’s fitness.
  • Natural selection results in changes in the inherited characteristics of a population.
  • Species of today look different from species of the past.
  • Each living species today has been descending with changes from its original parent. This principle is called descent with modifications.
  • All living organisms today descended from an original species. This principle is called common descent.
  • Descent with modifications has given rise to the study of phylogeny.
  • All living and extinct organisms were derived from a common ancestor, a single tree of life.

Darwin’s Evidence of Evolution

  • Fossils
  • Location of Fossils (Geographic Distribution)
  • Homologous Body structures: Structures that have developed from the same embryonic cells but have different mature forms.
  • Vestigial organs: Organs with little to no functions.
    • Example: Snake vestiges.

Key Evolutionary Concepts

  • Descent with Modifications: As organisms reproduce, they pass on traits to their offspring, but with slight changes or modifications over time.
  • Common Ancestor: The